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Deleterious effects of β-branched residues in the S1 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

Published online by Cambridge University Press:  01 January 2000

KATHERINE S. BATEMAN ,
STEPHEN ANDERSON ,
WUYUAN LU ,
M.A. QASIM ,
MICHAEL LASKOWSKI  and
MICHAEL N.G. JAMES
KATHERINE S. BATEMAN
Affiliation:
Medical Research Council of Canada Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
STEPHEN ANDERSON
Affiliation:
Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey 08854
WUYUAN LU
Affiliation:
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637
M.A. QASIM
Affiliation:
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
MICHAEL LASKOWSKI
Affiliation:
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
MICHAEL N.G. JAMES
Affiliation:
Medical Research Council of Canada Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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Abstract

Turkey ovomucoid third domain (OMTKY3) is a canonical inhibitor of serine proteinases. Upon complex formation, the inhibitors fully exposed P1 residue becomes fully buried in the preformed cavity of the enzyme. All 20 P1 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 P1 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 S1 binding pocket in SGPB, in contrast to that of the wild-type γ-branched P1 residue for OMTKY3, Leu18I. χ1 angles of approximately 40° are imposed on the side chains of Ile18I, Val18I, and Thr18I within the S1 pocket. Dihedral angles of +60°, −60°, or 180° are more commonly observed but 40° is not unfavorable for the β-branched side chains. Thr18I Oγ1 also forms a hydrogen bond with Ser195 Oγ in this orientation. The Ser18I side chain adopts two alternate conformations within the S1 pocket of SGPB, suggesting that the side chain is not stable in either conformation.

Keywords

association equilibrium constantsβ-branched amino acidsOMTKY3protein inhibitorserine proteinaseSGPBX-ray structure
Type
Research Article
Information
Protein Science , Volume 9 , Issue 1 , January 2000 , pp. 83 - 94
Copyright
© 2000 The Protein Society

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