Refined crystal structure of the molecular complex of Streptomyces griseus protease B, a serine protease, with the third domain of the ovomucoid inhibitor from turkey.

Abstract
The crystal structure of the molecular complex between Streptomyces griseus protease B (SGPB), a bacterial serine protease, and the third domain of the ovomucoid inhibitor from turkey was determined. Restrained-parameter least-squares refinement of the structure with the 1.8-.ANG. intensity data set has resulted in an R factor of 0.125. The carbonyl C atom of the reactive bond between Leu-18 and Glu-19 in the inhibitor lies at a distnace of 2.71 .ANG. from the O.gamma. atom of the nucleophilic Ser-195 in SGPB; this distance is 0.5 .ANG. shorter than a normal van der Waals contact. Unlike the reactive bond in the pancreatic trypsin inhibitor complexed with bovine trypsin, the Leu.sbd.Glu bond of the ovomucoid inhibitor is not distorted from planarity towards a pyramidal configuration.