title: X-ray and model-building studies on the specificity of the active site of proteinase K.
abstract: Proteinase K, the extracellular serine endopeptidase (E.C.3.4.21.14) from the fungus Tritirachium album limber, is homologous to the bacterial subtilisin proteases. The binding geometry of the synthetic inhibitor carbobenzoxy-Ala-Phechloromethyl ketone to the active site of proteinase K was first determined from a Fourier synthesis based on synchrotron X-ray diffraction data between 1.8 A and 5.0 A resolution. The protein inhibitor complex was refined by restrained least-squares minimization with the data between 10.0 and 1.8 A. The final R factor was 19.1%, and the model contained 2,018 protein atoms, 28 inhibitor atoms, 125 water molecules, and two Ca2+ ions. The peptide portion of the inhibitor is bound to the active center of proteinase K by means of a three-stranded antiparallel pleated sheet, with the side chain of the phenylalanine located in the P1 site. Model building studies, with lysine replacing phenylalanine in the inhibitor, explain the relatively unspecific catalytic activity of the enzyme.
authors.affiliation: European Molecular Biology Laboratory, Hamburg, Federal Republic of Germany.
authors.forename: C
authors.initials: C
authors.lastname: Betzel
authors.forename: M
authors.initials: M
authors.lastname: Bellemann
authors.forename: G P
authors.initials: GP
authors.lastname: Pal
authors.forename: J
authors.initials: J
authors.lastname: Bajorath
authors.forename: W
authors.initials: W
authors.lastname: Saenger
authors.forename: K S
authors.initials: KS
authors.lastname: Wilson
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003196:Computer Graphics; D019286:Endopeptidase K; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012697:Serine Endopeptidases / Q000032:analysis*; D015842:Serine Proteinase Inhibitors; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
chemical_list: D015842:Serine Proteinase Inhibitors; D012697:Serine Endopeptidases; D019286:Endopeptidase K