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PDBsum entry 1and
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Serine protease
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PDB id
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1and
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References listed in PDB file
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Key reference
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Title
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Structure of an engineered, Metal-Actuated switch in trypsin.
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Authors
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M.E.Mcgrath,
B.L.Haymore,
N.L.Summers,
C.S.Craik,
R.J.Fletterick.
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Ref.
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Biochemistry, 1993,
32,
1914-1919.
[DOI no: ]
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PubMed id
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Abstract
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The X-ray crystal structure of the copper complex of the rat trypsin mutant
Arg96 to His96 (trypsin R96H) has been determined in order to ascertain the
nature of the engineered metal-binding site and to understand the structural
basis for the metal-induced enzymatic inhibition. In the structure, the
catalytically essential His57 residue is reoriented out of the active-site
pocket and forms a chelating, metal-binding site with residue His96. The copper
is bound to the N epsilon 2 atoms of both histidine residues with Cu-N epsilon 2
= 2.2 A and N epsilon 2-Cu-N epsilon 2 = 89 degrees. The metal is clearly bound
to a third ligand leading to a distorted square planar geometry at Cu. The X-ray
results do not unambiguously yield the identity of this third ligand, but
chemical data suggest that it is a deprotonated, chelating Tris molecule which
was used as a carrier to solubilize the copper in alkaline solution (pH 8.0).
Upon reorientation of His57, a unique water molecule moves into the active site
and engages in hydrogen-bonding with Asp102-O delta 2 and His57-N delta 1.
Except for small movements of the peptide backbone near His96, the remainder of
the trypsin molecule is isostructural with the native enzyme. These data support
the notion that the effective inhibition of catalytic activity by metal ions
observed in trypsin R96H is indeed caused by a specific and reversible
reorganization of the active site in the enzyme.
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