Structure of the complex of Streptomyces griseus protease B and the third domain of the turkey ovomucoid inhibitor at 1.8-A resolution.
The structure of the complex between the serine protease Streptomyces griseus protease B (SGPB) and the third domain of the Kazal-type ovomucoid inhibitor from turkey has been solved at 1.8-A resolution and refined to a conventional R factor of 0.125. As others have reported previously for analogous complexes of proteases and protein inhibitors, the inhibitor binds in a fashion similar to that of a substrate; it is not cleaved, but there is a close approach (2.7 A) of the active site nucleophile Ser-195 O gamma to the carbonyl carbon of the reactive peptide bond of the inhibitor. Contrary to the structural reports regarding the other enzyme-inhibitor complexes, we conclude that there is no evidence for a significant distortion of this peptide bond from planarity. The mechanism of inhibition can be understood in terms of the equilibrium thermodynamic parameters Ka, the enzyme-inhibitor association constant, and Khyd, the equilibrium constant for inhibitor hydrolysis. These thermodynamic parameters can be rationalized in terms of the observed structure.
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D010450:Endopeptidases / Q000378:metabolism*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D012697:Serine Endopeptidases; D013305:Streptomyces griseus / Q000201:enzymology*; D014359:Trypsin Inhibitor, Kazal Pancreatic / Q000494:pharmacology*; D014361:Trypsin Inhibitors / Q000494:pharmacology*; D014422:Turkeys; D014961:X-Ray Diffraction
D014361:Trypsin Inhibitors; C039345:ovomucoid inhibitors; D014359:Trypsin Inhibitor, Kazal Pancreatic; D010450:Endopeptidases; D012697:Serine Endopeptidases; C024984:streptogrisin B