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Use getProperty "modelInfo" or getProperty "auxiliaryInfo" to inspect them. Default Van der Waals type for model set to Babel 46 atoms created ModelSet: not autobonding; use forceAutobond=true to force automatic bond creation Script completed Jmol script terminated
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| S-Adenosyl-L-homocysteine (SAH) is the biosynthetic precursor to homocysteine. SAH is formed by the demethylation of S-adenosyl-L-methionine. Adenosylhomocysteinase converts SAH into homocysteine and adenosine. |
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Read full article at Wikipedia
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InChI=1S/C14H20N6O5S/c15- 6(14(23)24)1-2-26-3-7-9(21)10(22)13(25-7)20-5-19-8-11(16)17-4-18-12(8)20/h4-7,9-10,13,21-22H,1-3,15H2,(H,23,24)(H2,16,17,18)/t6-,7+,9+,10+,13+/m0/s1 |
| ZJUKTBDSGOFHSH-WFMPWKQPSA-N |
| N[C@@H](CCSC[C@H]1O[C@H]([C@H](O)[C@@H]1O)n1cnc2c(N)ncnc12)C(O)=O |
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Mus musculus
(NCBI:txid10090)
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Source: BioModels - MODEL1507180067
See:
PubMed
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Saccharomyces cerevisiae
(NCBI:txid4932)
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Source: yeast.sf.net
See:
PubMed
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Escherichia coli
(NCBI:txid562)
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See:
PubMed
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Homo sapiens
(NCBI:txid9606)
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See:
DOI
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Bronsted base
A molecular entity capable of accepting a hydron from a donor (Bronsted acid).
(via organic amino compound )
Bronsted acid
A molecular entity capable of donating a hydron to an acceptor (Bronsted base).
(via oxoacid )
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fundamental metabolite
Any metabolite produced by all living cells.
cofactor
An organic molecule or ion (usually a metal ion) that is required by an enzyme for its activity. It may be attached either loosely (coenzyme) or tightly (prosthetic group).
EC 2.1.1.79 (cyclopropane-fatty-acyl-phospholipid synthase) inhibitor
An EC 2.1.1.* (methyltransferases) inhibitor that interferes with the action of cyclopropane fatty acid synthase (EC 2.1.1.79).
EC 2.1.1.72 [site-specific DNA-methyltransferase (adenine-specific)] inhibitor
An EC 2.1.1.* (methyltransferases) inhibitor that interferes with the action of site-specific DNA-methyltransferase (adenine-specific), EC 2.1.1.72.
epitope
The biological role played by a material entity when bound by a receptor of the adaptive immune system. Specific site on an antigen to which an antibody binds.
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View more via ChEBI Ontology
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S-(5'-deoxyadenosin-5'-yl)-L-homocysteine
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(2S)-2-amino-4-({[(2S,3S,4R,5R)-5-(6-amino-9H-purin-9-yl)-3,4-dihydroxytetrahydrofuran-2-yl]methyl}sulfanyl)butanoic acid
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PDBeChem
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2-S-adenosyl-L-homocysteine
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HMDB
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Adenosyl-L-homocysteine
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HMDB
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adenosylhomocysteine
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MetaCyc
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AdoHcy
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ChEBI
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S-(5'-adenosyl)-L-homocysteine
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HMDB
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S-(5'-adenosyl)-L-homocysteine
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ChEBI
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S-[1-(adenin-9-yl)-1,5-dideoxy-β-D-ribofuranos-5-yl]-L-homocysteine
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IUPAC
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S-Adenosyl-L-homocysteine
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KEGG COMPOUND
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S-ADENOSYL-L-HOMOCYSTEINE
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PDBeChem
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S-Adenosylhomocysteine
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KEGG COMPOUND
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SAH
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MetaCyc
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692100
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Gmelin Registry Number
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Gmelin
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979-92-0
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CAS Registry Number
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KEGG COMPOUND
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979-92-0
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CAS Registry Number
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ChemIDplus
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99188
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Reaxys Registry Number
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Reaxys
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Wu C, Tzertzinis G (2013)
Selection of a mimotope peptide of S-adenosyl-L-homocysteine and its application in immunoassays.
Molecules (Basel, Switzerland) 18, 13020-13026 [PubMed:24145794]
[show Abstract]
A competitive immunoassay for S-adenosyl-L-homocysteine (SAH) has been used in the clinical test for homocysteine via an enzymatic conversion reaction. Since S-adenosyl-l-homocysteine is a relatively unstable compound, we have used peptide library phage display to select a new mimotope peptide that interacts with the anti-SAH antibody. By immobilizing the synthetic peptide on solid phase as a competitive surrogate for SAH, we demonstrate its utility in a competitive ELISA assay. The linear range of the assay for SAH was 0.4-6.4 µM, in good correlation to the conventional assay using an SAH-conjugated plate. Our results show that the mimotope peptide has potential to substitute for SAH in immunoassays. | Köksal M, Chou WK, Cane DE, Christianson DW (2012)
Structure of geranyl diphosphate C-methyltransferase from Streptomyces coelicolor and implications for the mechanism of isoprenoid modification.
Biochemistry 51, 3003-3010 [PubMed:22455498]
[show Abstract]
Geranyl diphosphate C-methyltransferase (GPPMT) from Streptomyces coelicolor A3(2) is the first methyltransferase discovered that modifies an acyclic isoprenoid diphosphate, geranyl diphosphate (GPP), to yield a noncanonical acyclic allylic diphosphate product, 2-methylgeranyl diphosphate, which serves as the substrate for a subsequent cyclization reaction catalyzed by a terpenoid cyclase, methylisoborneol synthase. Here, we report the crystal structures of GPPMT in complex with GPP or the substrate analogue geranyl S-thiolodiphosphate (GSPP) along with S-adenosyl-L-homocysteine in the cofactor binding site, resulting from in situ demethylation of S-adenosyl-L-methionine, at 2.05 or 1.82 Å resolution, respectively. These structures suggest that both GPP and GSPP can undergo catalytic methylation in crystalline GPPMT, followed by dissociation of the isoprenoid product. S-Adenosyl-L-homocysteine remains bound in the active site, however, and does not exchange with a fresh molecule of cofactor S-adenosyl-L-methionine. These structures provide important clues about the molecular mechanism of the reaction, especially with regard to the face of the 2,3 double bond of GPP that is methylated as well as the stabilization of the resulting carbocation intermediate through cation-π interactions. | Buckoreelall K, Sun Y, Hobrath JV, Wilson L, Parker WB (2012)
Identification of Rv0535 as methylthioadenosine phosphorylase from Mycobacterium tuberculosis.
Tuberculosis (Edinburgh, Scotland) 92, 139-147 [PubMed:22225784]
[show Abstract]
5'-methylthioadenosine (MTA) is a natural purine that is metabolized by methylthioadenosine phosphorylase (MTAP, E.C 2.4.2.28) in Eukarya and Archaea but generally not in bacteria. In this work, Rv0535, which has been annotated as a probable MTAP in Mycobacterium tuberculosis, was expressed in and purified from Escherichia coli BL21 (DE3). The purified protein displayed properties of a phosphorylase and MTA was the preferred substrate. Adenosine and S-adenosyl-l-homocysteine were poor substrates and no activity was detected with 5'-methylthioinosine, the other natural purines, or the natural pyrimidines. Kinetic analysis of M. tuberculosis MTAP showed that the K(m) value for MTA was 9 μM. Rv0535 was estimated as a 30 kDa protein on a denaturing SDS-PAGE gel, which agreed with the molecular mass predicted by its gene sequence. Using gel filtration chromatography, the native molecular mass of the enzyme was determined to be 60 ± 4 kDa, and thus indicated that M. tuberculosis MTAP is a dimer. Differences in active site between mycobacterial and human MTAPs were identified by homology modeling based on the crystal of the human enzyme. A complete structure-activity relationship analysis could identify differences in substrate specificity between the two enzymes to aid in the development of purine-based, anti-tuberculosis drugs. | Tehlivets O (2011)
Homocysteine as a risk factor for atherosclerosis: is its conversion to s-adenosyl-L-homocysteine the key to deregulated lipid metabolism?
Journal of lipids 2011, 702853 [PubMed:21837278]
[show Abstract]
Homocysteine (Hcy) has been recognized for the past five decades as a risk factor for atherosclerosis. However, the role of Hcy in the pathological changes associated with atherosclerosis as well as the pathological mechanisms triggered by Hcy accumulation is poorly understood. Due to the reversal of the physiological direction of the reaction catalyzed by S-adenosyl-L-homocysteine hydrolase Hcy accumulation leads to the synthesis of S-adenosyl-L-homocysteine (AdoHcy). AdoHcy is a strong product inhibitor of S-adenosyl-L-methionine (AdoMet)-dependent methyltransferases, and to date more than 50 AdoMet-dependent methyltransferases that methylate a broad spectrum of cellular compounds including nucleic acids, proteins and lipids have been identified. Phospholipid methylation is the major consumer of AdoMet, both in mammals and in yeast. AdoHcy accumulation induced either by Hcy supplementation or due to S-adenosyl-L-homocysteine hydrolase deficiency results in inhibition of phospholipid methylation in yeast. Moreover, yeast cells accumulating AdoHcy also massively accumulate triacylglycerols (TAG). Similarly, Hcy supplementation was shown to lead to increased TAG and sterol synthesis as well as to the induction of the unfolded protein response (UPR) in mammalian cells. In this review a model of deregulation of lipid metabolism in response to accumulation of AdoHcy in Hcy-associated pathology is proposed. | Park EY, Choi WS, Oh SI, Kim KN, Shin JS, Song HK (2009)
Biochemical and structural characterization of 5'-methylthioadenosine nucleosidases from Arabidopsis thaliana.
Biochemical and biophysical research communications 381, 619-624 [PubMed:19249293]
[show Abstract]
5'-Methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH) are important metabolites in all living organisms. Two similar nucleosidases for hydrolyzing MTA in Arabidopsis thaliana (AtMTAN1 and AtMTAN2) exist, but only AtMTAN2 shows markedly broad substrate specificity for hydrolysis of SAH. To examine the biochemical characteristics of AtMTAN2, it was over-expressed in Escherichia coli and purified to homogeneity. Spectroscopic assays confirm AtMTAN2 catalyzes MTA as well as SAH hydrolysis, compared to AtMTAN1 which only hydrolyzes MTA. In addition, crystal structure of the AtMTAN2 enzyme in complex with, adenine was determined at 2.9A resolution. Finally, a structural comparison of AtMTAN2 performed with previously determined structures of AtMTAN1 and an E. coli homolog provides clues for the substrate specificity of MTA nucleosidases in A. thaliana. | Bollati M, Milani M, Mastrangelo E, Ricagno S, Tedeschi G, Nonnis S, Decroly E, Selisko B, de Lamballerie X, Coutard B, Canard B, Bolognesi M (2009)
Recognition of RNA cap in the Wesselsbron virus NS5 methyltransferase domain: implications for RNA-capping mechanisms in Flavivirus.
Journal of molecular biology 385, 140-152 [PubMed:18976670]
[show Abstract]
The mRNA-capping process starts with the conversion of a 5'-triphosphate end into a 5'-diphosphate by an RNA triphosphatase, followed by the addition of a guanosine monophosphate unit in a 5'-5' phosphodiester bond by a guanylyltransferase. Methyltransferases are involved in the third step of the process, transferring a methyl group from S-adenosyl-l-methionine to N7-guanine (cap 0) and to the ribose 2'OH group (cap 1) of the first RNA nucleotide; capping is essential for mRNA stability and proper replication. In the genus Flavivirus, N7-methyltransferase and 2'O-methyltransferase activities have been recently associated with the N-terminal domain of the viral NS5 protein. In order to further characterize the series of enzymatic reactions that support capping, we analyzed the crystal structures of Wesselsbron virus methyltransferase in complex with the S-adenosyl-l-methionine cofactor, S-adenosyl-l-homocysteine (the product of the methylation reaction), Sinefungin (a molecular analogue of the enzyme cofactor), and three different cap analogues (GpppG, (N7Me)GpppG, and (N7Me)GpppA). The structural results, together with those on other flaviviral methyltransferases, show that the capped RNA analogues all bind to an RNA high-affinity binding site. However, lack of specific interactions between the enzyme and the first nucleotide of the RNA chain suggests the requirement of a minimal number of nucleotides following the cap to strengthen protein/RNA interaction. Our data also show that, following incubation with guanosine triphosphate, Wesselsbron virus methyltransferase displays a guanosine monophosphate molecule covalently bound to residue Lys28, hinting at possible implications for the transfer of a guanine group to ppRNA. The structures of the Wesselsbron virus methyltransferase complexes obtained are discussed in the context of a model for N7-methyltransferase and 2'O-methyltransferase activities. | Garibotto G, Valli A, Anderstam B, Eriksson M, Suliman ME, Balbi M, Rollando D, Vigo E, Lindholm B (2009)
The kidney is the major site of S-adenosylhomocysteine disposal in humans.
Kidney international 76, 293-296 [PubMed:19357721]
[show Abstract]
S-adenosylhomocysteine (SAH), the metabolic precursor of homocysteine in the body, is a potent inhibitor of methylation reactions. Several methylation reactions play a major role in epigenetic regulation of protein expression, atherosclerosis, and cancer development. Here we studied the mechanisms responsible for the maintenance of circulating SAH levels by measurement of the arterio-venous differences across the kidney, splanchnic organs, and the lung in humans. The lungs did not remove or add any circulating SAH, whereas the liver released it into the hepatic veins. The kidney extracted 40% of SAH and the SAH arterio-venous difference across the kidney was directly and significantly related to its arterial levels. Thus, the kidney plays a major role in maintaining SAH levels and may, indirectly, control tissue transmethylation reactions. Our findings of a pivotal role for the human kidney in sulfur amino acid metabolism may also account for the increased plasma levels of SAH in patients with chronic kidney diseases. | Lin PY, Yang TH, Lin HG, Hu ML (2007)
Synergistic effects of S-adenosylhomocysteine and homocysteine on DNA damage in a murine microglial cell line.
Clinica chimica acta; international journal of clinical chemistry 379, 139-144 [PubMed:17300772]
[show Abstract]
BackgroundHomocysteine (Hcy) and S-adenosylhomocysteine (SAH) are 2 major metabolites of methionine. However, little is known about their interactions in human diseases.MethodsWe determined the interaction of Hcy with SAH on DNA damage (measured as comet formation) and DNA hypomethylation (assayed as 5-methyldeoxycytidine, 5-mdc) in BV-2 cells (immortalized murine microglia).ResultsHcy at 100 micromol/l and SAH at 4 micromol/l alone caused little DNA strand breaks, whereas 100 micromol/l Hcy in combination with 0.5 to 4 micromol/l SAH led to marked DNA damage and uracil misincorporation. The combination of 100 micromol/l Hcy with 4 micromol/l SAH (SAH+Hcy) significantly increased intracellular H(2)O(2), and the DNA damage induced by SAH+Hcy was strongly inhibited by addition of superoxide dismutase, catalase or desferrioxamine, suggesting the involvement of reactive oxygen species. DNA damage induced by SAH+Hcy may also involve DNA hypomethylation (i.e., decreased %5-mdc) because of the high correlation between them. The effects induced by SAH+Hcy were specific to SAH but not to Hcy because they were markedly decreased by replacing SAH with adenosine (4.0 micromol/l) but was not affected by replacing Hcy with cysteine (100 micromol/l).ConclusionSAH in combination with Hcy can cause synergistic DNA damage in BV-2 cells. It remains to be seen whether some of the Hcy-related diseases may be caused by a collaborative action of Hcy with SAH. | Castrillo JI, Zeef LA, Hoyle DC, Zhang N, Hayes A, Gardner DC, Cornell MJ, Petty J, Hakes L, Wardleworth L, Rash B, Brown M, Dunn WB, Broadhurst D, O'Donoghue K, Hester SS, Dunkley TP, Hart SR, Swainston N, Li P, Gaskell SJ, Paton NW, Lilley KS, Kell DB, Oliver SG (2007)
Growth control of the eukaryote cell: a systems biology study in yeast.
Journal of biology 6, 4 [PubMed:17439666]
[show Abstract]
BackgroundCell growth underlies many key cellular and developmental processes, yet a limited number of studies have been carried out on cell-growth regulation. Comprehensive studies at the transcriptional, proteomic and metabolic levels under defined controlled conditions are currently lacking.ResultsMetabolic control analysis is being exploited in a systems biology study of the eukaryotic cell. Using chemostat culture, we have measured the impact of changes in flux (growth rate) on the transcriptome, proteome, endometabolome and exometabolome of the yeast Saccharomyces cerevisiae. Each functional genomic level shows clear growth-rate-associated trends and discriminates between carbon-sufficient and carbon-limited conditions. Genes consistently and significantly upregulated with increasing growth rate are frequently essential and encode evolutionarily conserved proteins of known function that participate in many protein-protein interactions. In contrast, more unknown, and fewer essential, genes are downregulated with increasing growth rate; their protein products rarely interact with one another. A large proportion of yeast genes under positive growth-rate control share orthologs with other eukaryotes, including humans. Significantly, transcription of genes encoding components of the TOR complex (a major controller of eukaryotic cell growth) is not subject to growth-rate regulation. Moreover, integrative studies reveal the extent and importance of post-transcriptional control, patterns of control of metabolic fluxes at the level of enzyme synthesis, and the relevance of specific enzymatic reactions in the control of metabolic fluxes during cell growth.ConclusionThis work constitutes a first comprehensive systems biology study on growth-rate control in the eukaryotic cell. The results have direct implications for advanced studies on cell growth, in vivo regulation of metabolic fluxes for comprehensive metabolic engineering, and for the design of genome-scale systems biology models of the eukaryotic cell. | Wood RJ, Maynard-Smith MD, Robinson VL, Oyston PC, Titball RW, Roach PL (2007)
Kinetic analysis of Yersinia pestis DNA adenine methyltransferase activity using a hemimethylated molecular break light oligonucleotide.
PloS one 2, e801 [PubMed:17726531]
[show Abstract]
BackgroundDNA adenine methylation plays an important role in several critical bacterial processes including mismatch repair, the timing of DNA replication and the transcriptional control of gene expression. The dependence of bacterial virulence on DNA adenine methyltransferase (Dam) has led to the proposal that selective Dam inhibitors might function as broad spectrum antibiotics.Methodology/principal findingsHerein we report the expression and purification of Yersinia pestis Dam and the development of a continuous fluorescence based assay for DNA adenine methyltransferase activity that is suitable for determining the kinetic parameters of the enzyme and for high throughput screening against potential Dam inhibitors. The assay utilised a hemimethylated break light oligonucleotide substrate containing a GATC methylation site. When this substrate was fully methylated by Dam, it became a substrate for the restriction enzyme DpnI, resulting in separation of fluorophore (fluorescein) and quencher (dabcyl) and therefore an increase in fluorescence. The assays were monitored in real time using a fluorescence microplate reader in 96 well format and were used for the kinetic characterisation of Yersinia pestis Dam, its substrates and the known Dam inhibitor, S-adenosylhomocysteine. The assay has been validated for high throughput screening, giving a Z-factor of 0.71+/-0.07 indicating that it is a sensitive assay for the identification of inhibitors.Conclusions/significanceThe assay is therefore suitable for high throughput screening for inhibitors of DNA adenine methyltransferases and the kinetic characterisation of the inhibition. | Chin HG, Patnaik D, Estève PO, Jacobsen SE, Pradhan S (2006)
Catalytic properties and kinetic mechanism of human recombinant Lys-9 histone H3 methyltransferase SUV39H1: participation of the chromodomain in enzymatic catalysis.
Biochemistry 45, 3272-3284 [PubMed:16519522]
[show Abstract]
Histone H3 lysine 9 (H3K9) methylation is a major component of gene regulation and chromatin organization. SUV39H1 methylates H3K9 at the pericentric heterochromatin region and participates in the maintenance of genome stability. In this study, a recombinant purified SUV39H1 is used for substrate specificity and steady-state kinetic analysis with peptides representing the un- or dimethylated lysine 9 histone H3 tail or full-length human recombinant H3 (rH3). Recombinant SUV39H1 methylated its substrate via a nonprocessive mechanism. Binding of either peptide or AdoMet first to the enzyme made a catalytically competent binary complex. Product inhibition studies with SUV39H1 showed that S-adenosyl-l-homocysteine is a competitive inhibitor of S-adenosyl-l-methionine and a mixed inhibitor of substrate peptide. Similarly, the methylated peptide was a competitive inhibitor of the unmethylated peptide and a mixed inhibitor of AdoMet, suggesting a random mechanism in a bi-bi reaction for recombinant SUV39H1 in which either substrate can bind to the enzyme first and either product can release first. The turnover numbers (k(cat)) for the H3 tail peptide and rH3 were comparable (12 and 8 h(-)(1), respectively) compared to the value of 1.5 h(-)(1) for an identical dimethylated lysine 9 H3 tail peptide. The Michaelis constant for the methylated peptide (K(m)(pep)) was 13-fold lower compared to that of the unmethylated peptide. The Michaelis constants for AdoMet (K(m)(AdoMet)) were 12 and 6 microM for the unmethylated peptide substrate and rH3, respectively. A reduction in the level of methylation was observed at high concentrations of rH3, implying substrate inhibition. Deletion of the chromodomain or point mutation of the conserved amino acids, W64A or W67A, of SUV39H1 impaired enzyme activity despite the presence of an intact catalytic SET domain. Thus, SUV39H1 utilizes both the chromodomain and the SET domain for catalysis. | Jabs K, Koury MJ, Dupont WD, Wagner C (2006)
Relationship between plasma S-adenosylhomocysteine concentration and glomerular filtration rate in children.
Metabolism: clinical and experimental 55, 252-257 [PubMed:16423634]
[show Abstract]
S-Adenosylhomocysteine (SAH) is the metabolic precursor of all the homocysteine (Hcy) produced in the body. It is formed by the enzyme SAH hydrolase in a reversible reaction. In a previous study we have shown that plasma SAH is a more sensitive indicator of the risk for cardiovascular disease, and in a second study involving patients with renal disease, we also showed that it is a more sensitive indicator of renal insufficiency than plasma Hcy. However, in the latter study, the patients with renal disease were older and had a variety of other diseases such as diabetes and primary hypertension, which are associated with vascular disease and which could reduce renal function by involvement of the kidneys. Our objective was to rule out these complicating factors as the cause of the elevated SAH in renal disease and determine whether renal insufficiency alone was the cause of the elevated SAH. We therefore measured SAH, Hcy, folate, and vitamin B12 in 23 patients between the ages of 1 and 18 years with a wide range of renal function, but who had none of these complicating factors. Glomerular filtration rate (GFR) was calculated using serum creatinine according to the Schwartz formula. None of the children were deficient in folate or vitamin B12. After adjusting for age, folate, and vitamin B12, there was a modest and insignificant decrease of 0.033 micromol/L of Hcy associated with an increase of 1 mL/min of GFR (95% confidence interval, -0.066 to 0.0002). However, there was a strong and statistically significant association between log(SAH) and log(GFR): P < .0005, R2 = 0.76. This result suggests that plasma SAH rather than Hcy is the metabolite primarily affected in renal disease. We suggest that plasma Hcy elevations that have been linked to vascular disease may be due to elevated SAH resulting from renal insufficiency. | Yang TH, Hu ML (2006)
Intracellular levels of S-adenosylhomocysteine but not homocysteine are highly correlated to the expression of nm23-H1 and the level of 5-methyldeoxycytidine in human hepatoma cells with different invasion activities.
Nutrition and cancer 55, 224-231 [PubMed:17044778]
[show Abstract]
Cellular methylation imbalance is associated with tumor progression, hepatic cancer, and cardiovascular disease. S-Adenosylhomocysteine (SAH) is an inhibitor of cellular methyltransferases, and increasing evidence suggests that SAH rather than homocysteine (Hcy) plays a crucial role in mediating these disorders related to methylation imbalance. The anti-metastatic gene nm23-H1 was recently identified in murine and human cancer lines, and the expressions of nm23-H1 mRNA and protein have been shown to be useful tumor invasion markers. We investigated the relationships of tumor cell invasion activities with the intracellular levels of SAH and Hcy and the level of DNA methylation (measured as the cellular content of 5-methyldeoxycytidine, 5-mdc) in four hepatocarcinoma cell lines (Sk-Hep1, J5, Hep-G2, Hep-3B) and one normal liver cell line (Chang's liver cells) with different invasion activities (Sk-Hep1 > J5 > Hep-G2 = Hep-3B > Chang's liver cells). We found that the intracellular level of SAH was the highest in SK-Hep1 cells and was correlated with the invasion activities (r = 0.75, P = 0.008), whereas the level of intracellular Hcy was the highest in Chang's liver cells and was not significantly correlated with the invasion activities of these cell lines (r = 0.24, P = 0.38). The levels of 5-mdc increased with decreasing invasion activities of these cell lines (r = 0.82, P = 0.002), that is, the order of DNA hypomethylation in these cell lines was Sk-Hep1 > J5 > Hep-G2 = Hep-3B > Chang's liver cells, because the lower levels of 5-mdc% represent the higher DNA hypomethylation. Thus, our results demonstrate that SAH rather than Hcy is associated with invasion activities of hepatoma cells, and they suggest that SAH may play an important role in the invasion activities through DNA hypomethylation. | Shu S, Mahadeo DC, Liu X, Liu W, Parent CA, Korn ED (2006)
S-adenosylhomocysteine hydrolase is localized at the front of chemotaxing cells, suggesting a role for transmethylation during migration.
Proceedings of the National Academy of Sciences of the United States of America 103, 19788-19793 [PubMed:17172447]
[show Abstract]
Chemotaxis of bacteria requires regulated methylation of chemoreceptors. However, despite considerable effort in the 1980s, transmethylation has never been established as a component of eukaryotic cell chemotaxis. S-adenosylhomocysteine (SAH), the product formed when the methyl group of the universal donor S-adenosylmethionine (SAM) is transferred to an acceptor molecule, is a potent inhibitor of all transmethylation reactions. In eukaryotic cells, this inhibition is relieved by hydrolysis of SAH to adenosine and homocysteine catalyzed by SAH hydrolase (SAHH). We now report that SAHH, which is diffuse in the cytoplasm of nonmotile Dictyostelium amoebae and human neutrophils, concentrates with F-actin in pseudopods at the front of motile, chemotaxing cells, but is not present in filopodia or at the very leading edge. Tubercidin, an inhibitor of SAHH, inhibits both chemotaxis and chemotaxis-dependent cell streaming of Dictyostelium, and chemotaxis of neutrophils at concentrations that have little effect on cell viability. Tubercidin does not inhibit starvation-induced expression of the cAMP receptor, cAR1, or G protein-mediated stimulation of adenylyl cyclase activity and actin polymerization in Dictyostelium. Tubercidin has no effect on either capping of Con A receptors or phagocytosis in Dictyostelium. These results add SAHH to the list of proteins that redistribute in response to chemotactic signals in Dictyostelium and neutrophils and strongly suggest a role for transmethylation in chemotaxis of eukaryotic cells. | Kharbanda KK, Rogers DD, Mailliard ME, Siford GL, Barak AJ, Beckenhauer HC, Sorrell MF, Tuma DJ (2005)
Role of elevated S-adenosylhomocysteine in rat hepatocyte apoptosis: protection by betaine.
Biochemical pharmacology 70, 1883-1890 [PubMed:16253211]
[show Abstract]
Previous studies from our laboratory have shown that ethanol consumption results in an increase in hepatocellular S-adenosylhomocysteine levels. Because S-adenosylhomocysteine is a potent inhibitor of methylation reactions, we propose that increased intracellular S-adenosylhomocysteine levels could be a major contributor to ethanol-induced pathologies. To test this hypothesis, hepatocytes isolated from rat livers were grown on collagen-coated plates in Williams' medium E containing 5% FCS and exposed to varying concentrations of adenosine in order to increase intracellular S-adenosylhomocysteine levels. We observed increases in caspase-3 activity following exposure to adenosine. This increase in caspase activity correlated with increases in intracellular S-adenosylhomocysteine levels and DNA hypoploidy. The adenosine-induced changes could be significantly attenuated by betaine administration. The mechanism of betaine action appeared to be via the methylation reaction catalyzed by betaine-homocysteine-methyltransferase. To conclude, our results indicate that the elevation of S-adenosylhomocysteine levels in the liver by ethanol is a major factor in altering methylation reactions and in increasing apoptosis in the liver. We conclude that ethanol-induced alteration in methionine metabolic pathways may play a crucial role in the pathologies associated with alcoholic liver injury and that betaine administration may have beneficial therapeutic effects. | van Guldener C, Stam F, Stehouwer CD (2005)
Hyperhomocysteinaemia in chronic kidney disease: focus on transmethylation.
Clinical chemistry and laboratory medicine 43, 1026-1031 [PubMed:16197293]
[show Abstract]
Hyperhomocysteinaemia almost invariably occurs in patients with end-stage renal disease (ESRD), but there is debate whether, within the group of ESRD patients, higher or lower plasma homocysteine concentrations are related to an increased risk of vascular disease. Homocysteine is thought to be vasculotoxic in high concentrations, but it may also lead to elevated levels of its precursor, S-adenosylhomocysteine (AdoHcy), which is a potent inhibitor of the transmethylation pathway, in which S-adenosylmethionine (AdoMet) donates its methyl group to a variety of acceptors. Impairment of this transmethylation pathway in ESRD patients has been suggested by high AdoHcy levels, decreased AdoMet/AdoHcy ratios, decreased protein repair requiring methyltransferases, and by DNA hypomethylation. Stable isotope techniques using labelled methionine have indeed demonstrated a decreased whole body transmethylation flux in ESRD patients. These studies have also shown that folic acid treatment is capable of restoring transmethylation rates to normal values. The remaining hyperhomocysteinaemia after folic acid treatment in ESRD is probably due to a persistent impairment of homocysteine clearance through transsulphuration. DNA hypomethylation with its concurrent alterations in gene expression is largely improved by folate treatment. The adverse effects of hyperhomocysteinaemia in ESRD may thus be related to impaired transmethylation. Normalisation of plasma homocysteine does not seem to be required to restore transmethylation to normal levels in ESRD patients. | Geisel J, Schorr H, Bodis M, Isber S, Hübner U, Knapp JP, Obeid R, Herrmann W (2005)
The vegetarian lifestyle and DNA methylation.
Clinical chemistry and laboratory medicine 43, 1164-1169 [PubMed:16197315]
[show Abstract]
Vegetarians have a lower intake of vitamin B12 than omnivores do. Vitamin B12 deficiency (holotranscobalamin II <35 pmol/L or methylmalonic acid >271 nmol/L) was found in 58% of 71 vegetarians studied. Higher homocysteine levels (>12 micromol/L) found in 45% indicate disturbed remethylation of homocysteine to methionine. The methylation of DNA is strongly linked to homocysteine metabolism. Since DNA methylation is an important epigenetic factor in the regulation of gene expression, alteration of the methylation pattern has been associated with aging, cancer, atherosclerosis and other diseases. Three observations indicate that DNA methylation could be diminished by a vegetarian lifestyle. The vegetarian diet has a low content of methionine, remethylation of homocysteine is reduced by vitamin B12 deficiency and elevated homocysteine levels can induce the generation of S-adenosylhomocysteine (SAH), a potent inhibitor of methyltransferases. In our study we observed a significant correlation between SAH and whole-genome methylation (r=-0.36, p<0.01). This observation underlines the role of SAH as a potent inhibitor of methyltransferases. The methylation status was not correlated with homocysteine or S-adenosylemethionine (SAM). These results indicate that the degree of methylation does not depend on the supply of methyl groups and that the reverse generation of SAH has no influence. In addition to whole-genome methylation, the specific promoter methylation of the p66Shc gene was studied. However, the latter did not correlate with SAH, SAM or homocysteine. Obviously, the promoter methylation of the p66Shc gene is controlled in a specific way, without following the general regulating influence of SAH. In conclusion, an inhibitory effect of SAH on whole-genome methylation was found, but from our data no interaction between vegetarian lifestyle and DNA methylation could be determined. | Lee JE, Smith GD, Horvatin C, Huang DJ, Cornell KA, Riscoe MK, Howell PL (2005)
Structural snapshots of MTA/AdoHcy nucleosidase along the reaction coordinate provide insights into enzyme and nucleoside flexibility during catalysis.
Journal of molecular biology 352, 559-574 [PubMed:16109423]
[show Abstract]
MTA/AdoHcy nucleosidase (MTAN) irreversibly hydrolyzes the N9-C1' bond in the nucleosides, 5'-methylthioadenosine (MTA) and S-adenosylhomocysteine (AdoHcy) to form adenine and the corresponding thioribose. MTAN plays a vital role in metabolic pathways involving methionine recycling, biological methylation, polyamine biosynthesis, and quorum sensing. Crystal structures of a wild-type (WT) MTAN complexed with glycerol, and mutant-enzyme and mutant-product complexes have been determined at 2.0A, 2.0A, and 2.1A resolution, respectively. The WT MTAN-glycerol structure provides a purine-free model and in combination with the previously solved thioribose-free MTAN-ADE structure, we now have separate apo structures for both MTAN binding subsites. The purine and thioribose-free states reveal an extensive enzyme-immobilized water network in their respective binding subsites. The Asp197Asn MTAN-MTA and Glu12Gln MTAN-MTR.ADE structures are the first enzyme-substrate and enzyme-product complexes reported for MTAN, respectively. These structures provide representative snapshots along the reaction coordinate and allow insight into the conformational changes of the enzyme and the nucleoside substrate. A "catalytic movie" detailing substrate binding, catalysis, and product release is presented. | Porcelli M, Moretti MA, Concilio L, Forte S, Merlino A, Graziano G, Cacciapuoti G (2005)
S-adenosylhomocysteine hydrolase from the archaeon Pyrococcus furiosus: biochemical characterization and analysis of protein structure by comparative molecular modeling.
Proteins 58, 815-825 [PubMed:15645450]
[show Abstract]
S-adenosylhomocysteine hydrolase (AdoHcyHD) is an ubiquitous enzyme that catalyzes the breakdown of S-adenosylhomocysteine, a powerful inhibitor of most transmethylation reactions, to adenosine and L-homocysteine. AdoHcyHD from the hyperthermophilic archaeon Pyrococcus furiosus (PfAdoHcyHD) was cloned, expressed in Escherichia coli, and purified. The enzyme is thermoactive with an optimum temperature of 95 degrees C, and thermostable retaining 100% residual activity after 1 h at 90 degrees C and showing an apparent melting temperature of 98 degrees C. The enzyme is a homotetramer of 190 kDa and contains four cysteine residues per subunit. Thiol groups are not involved in the catalytic process whereas disulfide bond(s) could be present since incubation with 0.8 M dithiothreitol reduces enzyme activity. Multiple sequence alignment of hyperthermophilic AdoHcyHD reveals the presence of two cysteine residues in the N-terminus of the enzyme conserved only in members of Pyrococcus species, and shows that hyperthermophilic AdoHcyHD lack eight C-terminal residues, thought to be important for structural and functional properties of the eukaryotic enzyme. The homology-modeled structure of PfAdoHcyHD shows that Trp220, Tyr181, Tyr184, and Leu185 of each subunit and Ile244 from a different subunit form a network of hydrophobic and aromatic interactions in the central channel formed at the subunits interface. These contacts partially replace the interactions of the C-terminal tail of the eukaryotic enzyme required for tetramer stability. Moreover, Cys221 and Lys245 substitute for Thr430 and Lys426, respectively, of the human enzyme in NAD-binding. Interestingly, all these residues are fairly well conserved in hyperthermophilic AdoHcyHDs but not in mesophilic ones, thus suggesting a common adaptation mechanism at high temperatures. | Guérard C, Bréard M, Courtois F, Drujon T, Ploux O (2004)
Synthesis and evaluation of analogues of S-adenosyl-L-methionine, as inhibitors of the E. coli cyclopropane fatty acid synthase.
Bioorganic & medicinal chemistry letters 14, 1661-1664 [PubMed:15026045]
[show Abstract]
Analogues of S-adenosyl-L-methionine were synthesized and evaluated as inhibitors of the purified E. coli cyclopropane fatty acid synthase, a model for M. tuberculosis cyclopropane synthases that are potential targets for antituberculous drugs. Our results show that the presence of the adenosine moiety, in the inhibitor, is required for strong binding, but that the sulfonium charge is less important. The best inhibitors found were S-adenosyl-l-homocysteine and its sulfoxides. | Kennedy BP, Bottiglieri T, Arning E, Ziegler MG, Hansen LA, Masliah E (2004)
Elevated S-adenosylhomocysteine in Alzheimer brain: influence on methyltransferases and cognitive function.
Journal of neural transmission (Vienna, Austria : 1996) 111, 547-567 [PubMed:15057524]
[show Abstract]
Hyperhomocysteinemia is common in Alzheimer's disease and is negatively correlated with cognitive function. Hyperhomocysteinemia can increase S-adenosylhomocysteine (SAH), a potent methyltransferase inhibitor. This study investigates the role of brain SAH in the cognitive and neurological disruption in Alzheimer's disease. SAH was significantly (26%) higher in prefrontal cortex of Alzheimer patients than normals. Brain homogenates from Alzheimer patients inhibited an exogenous methyltransferase 15% more than normal homogenates (P <.001). Brain SAH levels correlated (r=.508) with methyltransferase inhibition by brain homogenates. Methyltransferase inhibition by Alzheimer brain homogenates correlated inversely with cognitive function as determined by MMSE (r=-0.36). Phenylethanolamine N-methyltransferase (PNMT) and catechol O-methyltransferase (COMT) activities were more than 30% lower (P<0.001) in Alzheimer than normal brains. Brain PNMT activity correlated significantly with cognitive function (r=0.243), age of Alzheimer's onset (r=0.272), and choline acetyltransferase activity (r=0.333), but negatively with neurofibrillary tangles (r=-0.332). COMT activity also correlated significantly with cognitive function (r=0.324), age of disease onset (r=0.209), choline acetyltransferase activity (r=0.326), levels of synaptophysin (r=0.506), and negatively with tangles (r=-0.216 P=0.039). Elevated SAH in Alzheimer brain inhibits methyltransferases and is related to markers of disease progression and cognitive impairment. | Li YJ, Stallcup MR, Lai MM (2004)
Hepatitis delta virus antigen is methylated at arginine residues, and methylation regulates subcellular localization and RNA replication.
Journal of virology 78, 13325-13334 [PubMed:15542683]
[show Abstract]
Hepatitis delta virus (HDV) contains a circular RNA which encodes a single protein, hepatitis delta antigen (HDAg). HDAg exists in two forms, a small form (S-HDAg) and a large form (L-HDAg). S-HDAg can transactivate HDV RNA replication. Recent studies have shown that posttranslational modifications, such as phosphorylation and acetylation, of S-HDAg can modulate HDV RNA replication. Here we show that S-HDAg can be methylated by protein arginine methyltransferase (PRMT1) in vitro and in vivo. The major methylation site is at arginine-13 (R13), which is in the RGGR motif of an RNA-binding domain. The methylation of S-HDAg is essential for HDV RNA replication, especially for replication of the antigenomic RNA strand to form the genomic RNA strand. An R13A mutation in S-HDAg inhibited HDV RNA replication. The presence of a methylation inhibitor, S-adenosyl-homocysteine, also inhibited HDV RNA replication. We further found that the methylation of S-HDAg affected its subcellular localization. Methylation-defective HDAg lost the ability to form a speckled structure in the nucleus and also permeated into the cytoplasm. These results thus revealed a novel posttranslational modification of HDAg and indicated its importance for HDV RNA replication. This and other results further showed that, unlike replication of the HDV genomic RNA strand, replication of the antigenomic RNA strand requires multiple types of posttranslational modification, including the phosphorylation and methylation of HDAg. | Ingrosso D, Cimmino A, Perna AF, Masella L, De Santo NG, De Bonis ML, Vacca M, D'Esposito M, D'Urso M, Galletti P, Zappia V (2003)
Folate treatment and unbalanced methylation and changes of allelic expression induced by hyperhomocysteinaemia in patients with uraemia.
Lancet (London, England) 361, 1693-1699 [PubMed:12767735]
[show Abstract]
BackgroundHyperhomocysteinaemia occurs in several genetically determined and acquired disorders and is highly prevalent in patients with uraemia. In these disorders, homocysteine precursor S-adenosylhomocysteine, a powerful competitive inhibitor of S-adenosylmethionine-dependent methyltransferases, is increased, suggesting unbalanced methylation. We aimed to investigate whether DNA hypomethylation is present in patients with uraemia who also have hyperhomocysteinaemia and whether regulation of specific classes of genes, dependent on DNA methylation, is compromised.MethodsWe selected men with hyperhomocysteinaemia and uraemia who were having standard haemodialysis treatment, and compared them with healthy male controls. We measured the homocysteine concentration from plasma samples and obtained DNA and RNA samples from peripheral mononuclear cells. DNA methylation was assessed by cytosine extension assay and by Southern blotting. Allelic expression of pseudoautosomal and imprinted genes was investigated by analysis of suitable restriction fragment length polymorphisms.FindingsTotal DNA hypomethylation was higher in patients than in controls (z score -4.593, p=0.0006) and allelic expression was changed in both sex-linked and imprinted genes. The shift from monoallelic to biallelic expression was dependent on homocysteine concentrations. Folate therapy, a common method to reduce hyperhomocysteinaemia, restored DNA methylation to normal levels and corrected the patterns of gene expression.InterpretationOur results suggest that hyperhomocysteinaemia affects epigenetic control of gene expression, which can be reverted by folate treatment. Our data support the hypothesis that the toxic action of homocysteine can be mediated by macromolecule hypomethylation. | Boison D, Scheurer L, Zumsteg V, Rülicke T, Litynski P, Fowler B, Brandner S, Mohler H (2002)
Neonatal hepatic steatosis by disruption of the adenosine kinase gene.
Proceedings of the National Academy of Sciences of the United States of America 99, 6985-6990 [PubMed:11997462]
[show Abstract]
Neonatal hepatic steatosis (OMIM 228100) is a fatal condition of unknown etiology characterized by a pale and yellow liver and early postnatal mortality. In the present study, a deficit in adenosine-dependent metabolism is proposed as a causative factor. Physiologically, adenosine is efficiently metabolized to AMP by adenosine kinase (ADK), an enzyme highly expressed in liver. ADK not only ensures normal adenine nucleotide levels but also is essential for maintaining S-adenosylmethionine-dependent transmethylation processes, where adenosine, an obligatory product, has to be constantly removed. Homozygous Adk(-/-) mutants developed normally during embryogenesis. However, within 4 days after birth they displayed microvesicular hepatic steatosis and died within 14 days with fatty liver. Adenine nucleotides were decreased and S-adenosylhomocysteine, a potent inhibitor of transmethylation reactions, was increased in the mutant liver. Thus, a deficiency in adenosine metabolism is identified as a powerful contributor to the development of neonatal hepatic steatosis, providing a model for the rapid development of postnatally lethal fatty liver. | Lehman-McKeeman LD, Gamsky EA, Hicks SM, Vassallo JD, Mar MH, Zeisel SH (2002)
Diethanolamine induces hepatic choline deficiency in mice.
Toxicological sciences : an official journal of the Society of Toxicology 67, 38-45 [PubMed:11961214]
[show Abstract]
The purpose of the present experiments was to test the hypothesis that diethanolamine (DEA), an alkanolamine shown to be hepatocarcinogenic in mice, induces hepatic choline deficiency and to determine whether altered choline homeostasis was causally related to the carcinogenic outcome. To examine this hypothesis, the biochemical and histopathological changes in male B6C3F1 mice made choline deficient by dietary deprivation were first determined. Phosphocholine (PCho), the intracellular storage form of choline was severely depleted, decreasing to about 20% of control values with 2 weeks of dietary choline deficiency. Other metabolites, including choline, glycerophosphocholine (GPC), and phosphatidylcholine (PC) also decreased. Hepatic concentrations of S-adenosylmethionine (SAM) decreased, whereas levels of S-adenosylhomocysteine (SAH) increased. Despite these biochemical changes, fatty liver, which is often associated with choline deficiency, was not observed in the mice. The dose response, reversibility, and strain-dependence of the effects of DEA on choline metabolites were studied. B6C3F1 mice were dosed dermally with DEA (0, 10, 20, 40, 80, and 160 mg/kg) for 4 weeks (5 days/week). Control animals received either no treatment or dermal application of 95% ethanol (1.8 ml/kg). PCho was most sensitive to DEA treatment, decreasing at dosages of 20 mg/kg and higher and reaching a maximum 50% depletion at 160 mg/kg/day. GPC, choline, and PC also decreased in a dose-dependent manner. At 80 and 160 mg/kg/day, SAM levels decreased while SAH levels increased in liver. A no-observed effect level (NOEL) for DEA-induced changes in choline homeostasis was 10 mg/kg/day. Choline metabolites, SAM and SAH returned to control levels in mice dosed at 160 mg/kg for 4 weeks and allowed a 2-week recovery period prior to necropsy. In a manner similar to dietary choline deficiency, no fatty change was observed in the liver of DEA-treated mice. In C57BL/6 mice, DEA treatment (160 mg/kg) also decreased PCho concentrations, without affecting hepatic SAM levels, suggesting that strain-specific differences in intracellular methyl group regulation may influence carcinogenic outcome with DEA treatment. Finally, in addition to the direct effects of DEA on choline homeostasis, dermal application of 95% ethanol for 4 weeks decreased hepatic betaine levels, suggesting that the use of ethanol as a vehicle for dermal application of DEA may exacerbate or confound the biochemical actions of DEA alone. Collectively, the results demonstrate that DEA treatment causes a spectrum of biochemical changes consistent with choline deficiency in mice and demonstrate a clear dose concordance between DEA-induced choline deficiency and hepatocarcinogenic outcome. | Griffith SC, Sawaya MR, Boutz DR, Thapar N, Katz JE, Clarke S, Yeates TO (2001)
Crystal structure of a protein repair methyltransferase from Pyrococcus furiosus with its L-isoaspartyl peptide substrate.
Journal of molecular biology 313, 1103-1116 [PubMed:11700066]
[show Abstract]
Protein L-isoaspartyl (D-aspartyl) methyltransferases (EC 2.1.1.77) are found in almost all organisms. These enzymes catalyze the S-adenosylmethionine (AdoMet)-dependent methylation of isomerized and racemized aspartyl residues in age-damaged proteins as part of an essential protein repair process. Here, we report crystal structures of the repair methyltransferase at resolutions up to 1.2 A from the hyperthermophilic archaeon Pyrococcus furiosus. Refined structures include binary complexes with the active cofactor AdoMet, its reaction product S-adenosylhomocysteine (AdoHcy), and adenosine. The enzyme places the methyl-donating cofactor in a deep, electrostatically negative pocket that is shielded from solvent. Across the multiple crystal structures visualized, the presence or absence of the methyl group on the cofactor correlates with a significant conformational change in the enzyme in a loop bordering the active site, suggesting a role for motion in catalysis or cofactor exchange. We also report the structure of a ternary complex of the enzyme with adenosine and the methyl-accepting polypeptide substrate VYP(L-isoAsp)HA at 2.1 A. The substrate binds in a narrow active site cleft with three of its residues in an extended conformation, suggesting that damaged proteins may be locally denatured during the repair process in cells. Manual and computer-based docking studies on different isomers help explain how the enzyme uses steric effects to make the critical distinction between normal L-aspartyl and age-damaged L-isoaspartyl and D-aspartyl residues. | Lim K, Zhang H, Tempczyk A, Bonander N, Toedt J, Howard A, Eisenstein E, Herzberg O (2001)
Crystal structure of YecO from Haemophilus influenzae (HI0319) reveals a methyltransferase fold and a bound S-adenosylhomocysteine.
Proteins 45, 397-407 [PubMed:11746687]
[show Abstract]
The crystal structure of YecO from Haemophilus influenzae (HI0319), a protein annotated in the sequence databases as hypothetical, and that has not been assigned a function, has been determined at 2.2-A resolution. The structure reveals a fold typical of S-adenosyl-L-methionine-dependent (AdoMet) methyltransferase enzymes. Moreover, a processed cofactor, S-adenosyl-L-homocysteine (AdoHcy), is bound to the enzyme, further confirming the biochemical function of HI0319 and its sequence family members. An active site arginine, shielded from bulk solvent, interacts with an anion, possibly a chloride ion, which in turn interacts with the sulfur atom of AdoHcy. The AdoHcy and nearby protein residues delineate a small solvent-excluded substrate binding cavity of 162 A(3) in volume. The environment surrounding the cavity indicates that the substrate molecule contains a hydrophobic moiety and an anionic group. Many of the residues that define the cavity are invariant in the HI0319 sequence family but are not conserved in other methyltransferases. Therefore, the substrate specificity of YecO enzymes is unique and differs from the substrate specificity of all other methyltransferases sequenced to date. Examination of the Enzyme Commission list of methyltransferases prompted a manual inspection of 10 possible substrates using computer graphics and suggested that the ortho-substituted benzoic acids fit best in the active site. |
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