Publications

• Purification and properties of 5-methyltetrahydropteroyltriglutamate-homocysteine transmethylase.

  Whitfield C.D., Steers E.J. Jr., Weissbach H.

  J Biol Chem 245:390-401(1970) [PubMed] [EuropePMC]

• Transfer of the methyl group from N5-methyltetrahydrofolates to homocysteine in Escherichia coli.

  Guest J.R., Friedman S., Foster M.A., Tejerina G., Woods D.D.

  Biochem J 92:497-504(1964) [PubMed] [EuropePMC]

• Vitamin-B12-independent methionine synthase from a higher plant (Catharanthus roseus). Molecular characterization, regulation, heterologous expression, and enzyme properties.

  Eichel J., Gonzalez J.C., Hotze M., Matthews R.G., Schroeder J.

  Methionine synthases catalyze the formation of methionine by the transfer of a methyl group from 5-methyltetrahydrofolate to homocysteine. This reaction is the last step in L-methionine biosynthesis, and it also serves to regenerate the methyl group of S-adenosylmethionine, a cofactor required for ... >> More

  Methionine synthases catalyze the formation of methionine by the transfer of a methyl group from 5-methyltetrahydrofolate to homocysteine. This reaction is the last step in L-methionine biosynthesis, and it also serves to regenerate the methyl group of S-adenosylmethionine, a cofactor required for biological methylation reactions. We describe the cloning, expression and characterization of a methionine synthase from the higher plant Catharanthus roseus. cDNAs were identified that encoded a protein of 85 kDa sharing 50% identify with the cobalamin-independent methionine synthase from Escherichia coli (MetE) and 41% identity with a partial sequence of a yeast homolog of MetE. The C. roseus protein was expressed at high levels in E. coli. The enzyme accepts the triglutamate form of methyltetrahydrofolate as a methyl donor but not the monoglutamate form, and it does not require S-adenosylmethionine or cobalamin for activity. The properties indicate that the enzyme is a cobalamin-independent methionine synthase (EC 2.1.1.14). In contrast to the E. coli MetE, the plant protein does not require phosphate or magnesium ions for activity. Immunoblots of plants extracts showed that the protein was localized in the cytosol, and was present in a variety of plant species. A nutritional downshift of the C. roseus cell culture revealed a strong, transient transcriptional activation, but no significant increment in the total level of the protein. The availability of the protein and the cDNA now provide tools to investigate the complexities of methionine biosynthesis in plants. << Less

  Eur. J. Biochem. 230:1053-1058(1995) [PubMed] [EuropePMC]

• Cobalamin-independent methionine synthase from Escherichia coli: a zinc metalloenzyme.

  Gonzalez J.C., Peariso K., Penner-Hahn J.E., Matthews R.G.

  Cobalamin-independent methionine synthase (MetE) from Escherichia coli catalyzes the transfer of a methyl group from methyltetrahydrofolate to homocysteine. Previous work had shown the existence of a reactive thiol group, cysteine 726, whose alkylation led to loss of all detectable enzymatic activ ... >> More

  Cobalamin-independent methionine synthase (MetE) from Escherichia coli catalyzes the transfer of a methyl group from methyltetrahydrofolate to homocysteine. Previous work had shown the existence of a reactive thiol group, cysteine 726, whose alkylation led to loss of all detectable enzymatic activity [González, J.C., et al. (1992) Biochemistry 31, 6045-6056]. A site-directed mutation of MetE, Cys726Ser, was constructed to investigate the possible role of this cysteine. The Cys726Ser protein was purified to homogeneity, affording a protein with no detectable activity. To assess the possibility that cysteine726 functions as a metal ligand, inductively coupled plasma-atomic emission spectrometry was performed. The wild-type enzyme contains 1.02 equiv of zinc per subunit; the Cys726Ser mutant does not contain zinc, supporting the view that cysteine726 is required for metal binding. A loss of enzymatic activity is observed upon removal of zinc from the wild-type MetE by incubation in urea and EDTA; activity can subsequently be restored by zinc reconstitution, suggesting that zinc is required for catalysis. Circular dichroism measurements further suggest that there are no major differences in the secondary structures of the wild-type and the Cys726Ser mutant enzymes. Extended X-ray absorption fine structure analysis has established that the average zinc environment is different in the presence of homocysteine than in its absence and is consistent with the changes expected for displacement of an oxygen or nitrogen ligand by the sulfur of homocysteine. A possible model for zinc-dependent activation of homocysteine by MetE is presented. << Less

  Biochemistry 35:12228-12234(1996) [PubMed] [EuropePMC]