title: Interactions of Streptomyces subtilisin inhibitor with Streptomyces griseus proteases A and B. Enzyme kinetic and computer simulation studies.
abstract: Streptomyces subtilisin inhibitor (SSI), a dimeric protein that strongly inhibits subtilisins, was shown to form tight inhibitory complexes with Streptomyces griseus proteases A and B (SGPA and SGPB). The apparent dissociation constants of the SGPA-SSI and SGPB-SSI complexes were found to be orders of magnitude less than those of subtilisin-SSI complexes. Using the known atomic coordinates for SGPA and SSI, the highly complementary nature of the surface geometries of the two proteins was confirmed by a computer graphics study, which led to a proposed structure for the SGPA-SSI complex. Kinetic studies further suggested that the SSI dimer can bind two molecules of either SGPA or SGPB, and the 2:1-complexes (consisting of one inhibitor dimer and one enzyme molecule) apparently possess lower intrinsic dissociation constants than the 2:2-complexes. It was also shown that both of SGPA and SGPB are inhibited by both soybean trypsin inhibitor (Kunitz) and bovine pancreatic trypsin inhibitor (Kunitz), but far less strongly than by SSI.
mesh_terms: D016282:Aspartic Acid Endopeptidases; D001426:Bacterial Proteins / Q000378:metabolism*; D003201:Computers; D010450:Endopeptidases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008954:Models, Biological; D011487:Protein Conformation; D013305:Streptomyces griseus / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; C018150:subtilisin inhibitor protein, Streptomyces; D010450:Endopeptidases; C022325:aspartic proteinase A; D016282:Aspartic Acid Endopeptidases