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Title
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Structure of the complex of Streptomyces griseus protease B and the third domain of the turkey ovomucoid inhibitor at 1.8-A resolution.
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Authors
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R.J.Read,
M.Fujinaga,
A.R.Sielecki,
M.N.James.
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Ref.
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Biochemistry, 1983,
22,
4420-4433.
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PubMed id
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Abstract
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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.
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