Premium
Deleterious effects of β‐branched residues in the S 1 specificity pocket of Streptomyces griseus proteinase B (SGPB): Crystal structures of the turkey ovomucoid third domain variants Ile18I, Val18I, Thr18I, and Ser18I in complex with SGPB
Author(s) -
Bateman Katherine S.,
James Michael N.G.,
Anderson Stephen,
Lu Wuyuan,
Qasim M.A.,
Laskowski Michael
Publication year - 2000
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.9.1.83
Subject(s) - streptomyces griseus , serine , side chain , dihedral angle , chemistry , stereochemistry , hydrogen bond , residue (chemistry) , serine proteinase inhibitors , crystallography , active site , crystal structure , hydrolase , enzyme , molecule , streptomyces , biochemistry , biology , serine protease , organic chemistry , genetics , protease , bacteria , polymer
Turkey ovomucoid third domain (OMTKY3) is a canonical inhibitor of serine proteinases. Upon complex formation, the inhibitors fully exposed P 1 residue becomes fully buried in the preformed cavity of the enzyme. All 20 P 1 variants of OMTKY3 have been obtained by recombinant DNA technology and their equilibrium association constants have been measured with six serine proteinases. To rationalize the trends observed in this data set, high resolution crystal structures have been determined for OMTKY3 P 1 variants in complex with the bacterial serine proteinase, Streptomyces griseus proteinase B (SGPB). Four high resolution complex structures are being reported in this paper; the three β‐branched variants, Ile18I, Val18I, and Thr18I, determined to 2.1, 1.6, and 1.7 Å resolution, respectively, and the structure of the Ser18I variant complex, determined to 1.9 Å resolution. Models of the Cys18I, Hse18I, and Ape18I variant complexes are also discussed. The β‐branched side chains are not complementary to the shape of the S 1 binding pocket in SGPB, in contrast to that of the wild‐type γ‐branched P 1 residue for OMTKY3, Leu18I. X 1 angles of approximately 40° are imposed on the side chains of Ile18I, Val18I, and Thr18I within the S 1 pocket. Dihedral angles of +60°, ‐60°, or 180° are more commonly observed but 40° is not unfavorable for the β‐branched side chains. Thr18I O γ1 also forms a hydrogen bond with Ser195 O γ in this orientation. The Ser18I side chain adopts two alternate conformations within the S 1 pocket of SGPB, suggesting that the side chain is not stable in either conformation.