title: The aspartic proteinase from Saccharomyces cerevisiae folds its own inhibitor into a helix.
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.
authors.affiliation: Macromolecular Crystallography Laboratory, Program in Structural Biology, National Cancer Institute-FCRDC, Frederick, Maryland 21702, USA.
authors.forename: M
authors.initials: M
authors.lastname: Li
authors.forename: L H
authors.initials: LH
authors.lastname: Phylip
authors.forename: W E
authors.initials: WE
authors.lastname: Lees
authors.forename: J R
authors.initials: JR
authors.lastname: Winther
authors.forename: B M
authors.initials: BM
authors.lastname: Dunn
authors.forename: A
authors.initials: A
authors.lastname: Wlodawer
authors.forename: J
authors.initials: J
authors.lastname: Kay
authors.forename: A
authors.initials: A
authors.lastname: Gustchina
mesh_terms: D000595:Amino Acid Sequence; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D005656:Fungal Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008715:Methionine; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins; D014357:Trypsin / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; C018134:PAI3 protein, S cerevisiae; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D008715:Methionine; D014357:Trypsin; C022325:aspartic proteinase A; C499267:PEP4 protein, S cerevisiae; D016282:Aspartic Acid Endopeptidases