Abstract
The functions of calnuc, a novel Ca(2+)-binding protein with multiple structural domains and diverse interacting partners, are yet unknown. We demonstrate unknown facets of calnuc, which is a serine protease in which Ser-378 of GXSXG motif, Asp-328 of DTG motif, and His-339 form the "catalytic triad," locating the enzyme active site in the C-terminal region. Analogous to the active site of Zn(2+) carboxypeptidases, calnuc has two high affinity (K(d) ∼ 20 nm), well conserved Zn(2+)-binding sites near its N terminus, although it is inactive as a peptidase. Zn(2+) binding allosterically and negatively regulates the serine protease activity of calnuc, inhibition being caused by an "open to close" change in its conformation not seen upon Ca(2+) binding. Most strikingly, interaction with G protein α subunit completely inhibits the enzymatic activity of calnuc. We thus illustrate that G proteins and Zn(2+) act as two "keys" that control enzymatic activity of calnuc, arresting it in "locked" state. Calnuc, therefore, exists dynamically in two different forms, (i) as a Ca(2+)-binding protein in Zn(2+)-bound form and (ii) as a protease in Zn(2+)-free form, commissioning it to perform multiple functions.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Allosteric Regulation
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Allosteric Site
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Amino Acid Sequence
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Animals
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Binding Sites
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Calcium / metabolism
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Calcium-Binding Proteins / chemistry
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Calcium-Binding Proteins / genetics
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Calcium-Binding Proteins / metabolism*
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Catalytic Domain
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DNA-Binding Proteins / chemistry
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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Escherichia coli / genetics
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GTP-Binding Protein alpha Subunits / chemistry
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GTP-Binding Protein alpha Subunits / genetics
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GTP-Binding Protein alpha Subunits / metabolism*
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Gene Expression
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Humans
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Kinetics
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Molecular Sequence Data
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Nerve Tissue Proteins / chemistry
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Nerve Tissue Proteins / genetics
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Nerve Tissue Proteins / metabolism*
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Nucleobindins
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Protein Binding
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Protein Conformation
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Recombinant Proteins / chemistry
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Sequence Alignment
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Sequence Homology, Amino Acid
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Serine Endopeptidases / chemistry
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Serine Endopeptidases / genetics
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Serine Endopeptidases / metabolism*
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Thermodynamics
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Zinc / chemistry
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Zinc / metabolism*
Substances
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Calcium-Binding Proteins
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DNA-Binding Proteins
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GTP-Binding Protein alpha Subunits
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Nerve Tissue Proteins
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Nucleobindins
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Recombinant Proteins
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Serine Endopeptidases
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Zinc
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Calcium