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Title
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Gamma-chymotrypsin is a complex of alpha-chymotrypsin with its own autolysis products.
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Authors
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M.Harel,
C.T.Su,
F.Frolow,
I.Silman,
J.L.Sussman.
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Ref.
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Biochemistry, 1991,
30,
5217-5225.
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PubMed id
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Abstract
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The determination of three separate gamma-chymotrypsin structures at different
temperatures and resolutions confirmed the presence of electron density in the
active site, which could be interpreted as an oligopeptide as had previously
been suggested by Dixon and Matthews [(1989) Biochemistry 28, 7033-7038]. HPLC
analyses of the enzyme before and after crystallization demonstrated the
presence of a wide variety of oligopeptides in the redissolved crystal, most
with COOH-terminal aromatic residues, as expected of the products of
chymotrypsin cleavage, which appeared to arise from extensive autolysis of the
enzyme under the crystallization conditions. The refined structures agree well
with the conformation of both gamma-chymotrypsin and alpha-chymotrypsin. The
electron density in the active site is thus interpreted as arising from a
repertoire of autolysed oligopeptides produced concomitantly with
crystallization. The COOH-terminal carbons of the polypeptide(s) display short
contact distances (1.97, 2.47, and 2.13 A, respectively) to Ser195 O gamma in
all three refined structures, but the electron density is not continuous between
these two atoms in any of them. This suggests that some sequences are covalently
bound as enzyme intermediates while others are noncovalently bound as
enzyme-product complexes.
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