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Page 1 (in Ch.7)
Page 2 Tertiary
Page 3 Active
Page 5 Reaction Mechanism Page 6 Crystal Structures Page 7 References
in loop between colour in domain strands: diagrams ______ ________ _________ Catalytic Triad His-57 side chain 1 3,4 red Asp-102 side chain 1 5,6 Ser-195 side chain 2 3,4 Oxyanion Hole Gly-193 main chain 2 3,4 white Ser-195 main chain 2 3,4 Specificity Pocket Ser-189 side chain 2 5,6 green Gly-216 side chain 2 5,6 Gly-226 side chain 2 3,4 Main Chain Ser-214 main chain 2 5,6 yellow Substrate Binding Trp-215 main chain 2 5,6 Gly-216 main chain 2 5,6 Tripeptide cleavage blue product
The following diagrams are of chymotrypsin complexed with a tripeptide (crystal structure 8gch). This tripeptide (Gly-Ala-Trp) is in fact a product of autolysis, i.e. a peptide fragment produced by the hydrolysis of chymotrypsin by another chymotrypsin molecule; refer to Part 1 . The large tryptophan side chain is situated inside the specificity pocket.
(Crystallography note: numerous different types of peptide fragment occurred in different chymotrypsin molecules in the protein crystal; this tripeptide results from the overlapping electron density of different asymmetric units.)
Views are shown both with and without the tripeptide fragment.
A view looking into the substrate-specificity pocket, without tripeptide:
The same view with tripeptide:
a different view to illustrate the main-chain hydrogen bonding to the substrate/product
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