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Title
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Crystal structure at 1.63 A resolution of the native form of porcine beta-trypsin: revealing an acetate ion binding site and functional water network.
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Authors
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A.Johnson,
N.Gautham,
V.Pattabhi.
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Ref.
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Biochim Biophys Acta, 1999,
1435,
7.
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PubMed id
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Abstract
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The active center of a serine protease is the catalytic triad composed of
His-57, Ser-195 and Asp-102. The existing crystal structure data on serine
proteases have not fully answered a number of fundamental questions relating to
the catalytic activity of serine proteases. The new high resolution native
porcine beta-trypsin (BPT) structure is aimed at extending the knowledge on the
conformation of the active site and the ordered water structure within and
around the active site. The crystal structure of BPT has been determined at 1.63
A resolution. An acetate ion bound at the active site of a trypsin molecule by
both classical hydrogen bonds and C-HellipsisO hydrogen bonds has been
identified for the first time. A large network of water molecules extending from
the recognition amino acid Asp-184 to the entry of the active site has been
observed in the BPT structure. A detailed comparison with inhibitor complexes
and autolysates indicates that the sulfate ion and the acetate ion bind at the
same site of the trypsin molecule. The Ser-195 Cbeta-Ogamma-His-57 Nepsilon
angle in the catalytic triad of BPT is intermediate between the corresponding
values of the complex and native structure due to acetate ion binding. The
network of waters from the recognition amino acid to the active site entry is
probably the first ever complete picture of functional waters around the active
site. Structural comparisons show that the functional waters involved in the
binding of small molecule inhibitors and protease inhibitors are distinctly
different.
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