Abstract
Aspartic proteinase A from yeast is specifically and potently inhibited by a small protein called IA3 from Saccharomyces cerevisiae. Although this inhibitor consists of 68 residues, we show that the inhibitory activity resides within the N-terminal half of the molecule. Structures solved at 2.2 and 1.8 A, respectively, for complexes of proteinase A with full-length IA3 and with a truncated form consisting only of residues 2-34, reveal an unprecedented mode of inhibitor-enzyme interactions. Neither form of the free inhibitor has detectable intrinsic secondary structure in solution. However, upon contact with the enzyme, residues 2-32 become ordered and adopt a near-perfect alpha-helical conformation. Thus, the proteinase acts as a folding template, stabilizing the helical conformation in the inhibitor, which results in the potent and specific blockage of the proteolytic activity.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Aspartic Acid Endopeptidases / antagonists & inhibitors*
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Aspartic Acid Endopeptidases / chemistry*
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Aspartic Acid Endopeptidases / metabolism
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Circular Dichroism
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Crystallography, X-Ray
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Fungal Proteins / antagonists & inhibitors*
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Fungal Proteins / chemistry*
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Fungal Proteins / genetics
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Fungal Proteins / metabolism
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Hydrogen-Ion Concentration
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Methionine
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Models, Molecular
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Molecular Sequence Data
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Mutation
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Protein Conformation
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Protein Folding
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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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Saccharomyces cerevisiae / enzymology*
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Saccharomyces cerevisiae Proteins*
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Trypsin / metabolism
Substances
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Fungal Proteins
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PAI3 protein, S cerevisiae
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Recombinant Proteins
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Saccharomyces cerevisiae Proteins
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Methionine
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Trypsin
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aspartic proteinase A
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PEP4 protein, S cerevisiae
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Aspartic Acid Endopeptidases