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Title
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Crystal and molecular structure of chymotrypsin inhibitor 2 from barley seeds in complex with subtilisin Novo.
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Authors
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C.A.McPhalen,
I.Svendsen,
I.Jonassen,
M.N.James.
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Ref.
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Proc Natl Acad Sci U S A, 1985,
82,
7242-7246.
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PubMed id
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Abstract
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The serine proteinase inhibitor from barley seeds, chymotrypsin inhibitor
2(CI-2), has been crystallized in a molecular complex with subtilisin Novo (EC
3.4.21.14). The crystal structure of this complex has been determined at 2.1-A
resolution by the molecular replacement method and partially refined by
restrained-parameter least-squares methods. The present crystallographic R
factor (SigmaFo[unk] - [unk]Fc/Sigma[unk]Fo[unk]) is 0.193. CI-2 is a member of
the potato inhibitor 1 family; it is a serine proteinase inhibitor lacking
disulfide bonds. Comparison of the subtilisin molecule in this complex with the
native subtilisin shows that the two molecules are very similar in structure.
The inhibitor binds in a mode presumably resembling that of a true substrate,
but it is not cleaved. This is in accord with the reported structures of other
serine proteinase-inhibitor complexes. CI-2 consists of a four-stranded mixed
parallel and antiparallel beta-sheet against which an alpha-helix packs to form
a hydrophobic core. A wide loop crossover connection between parallel strands 2
and 3 of the beta-sheet contains the reactive-site bond. The conformation of the
four residues to either side of the reactive-site bond is similar to that of the
analogous residues in the third domain of the turkey ovomucoid inhibitor (Kazal
family); the overall polypeptide chain fold of these inhibitors and the location
of the reactive site in the respective chains are different.
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