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PDBsum entry 1pj8
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Hydrolase/hydrolase substrate
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PDB id
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1pj8
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Contents |
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* Residue conservation analysis
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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 a ternary complex of proteinase k, Mercury, And a substrate-Analogue hexa-Peptide at 2.2 a resolution.
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Authors
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A.K.Saxena,
T.P.Singh,
K.Peters,
S.Fittkau,
M.Visanji,
K.S.Wilson,
C.Betzel.
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Ref.
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Proteins, 1996,
25,
195-201.
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PubMed id
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Abstract
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The crystal structure of a ternary complex of proteinase K, Hg(II) and a
hexapeptide N-Ac-Pro-Ala-Pro-Phe-Pro-Ala-NH2 has been determined at 2.2 A
resolution and refined to an R factor of 0.172 for 12,910 reflections. The
mercury atom occupies two alternate sites, each of which was assigned an
occupancy of 0.45. These two sites are bridged by Cys-73 S gamma which forms
covalent bonds to both. Both mercury sites form regular polyhedrons involving
atoms from residues Asp-39, His-69, Cys-73, His-72, Met-225, and Wat-324. The
complex formation with mercury seems to disturb the stereochemistry of the
residues of the catalytic triad Asp-39, His-69, and Ser-224 appreciably, thus
reducing the enzymatic activity of proteinase K to 15%. The electron density in
the difference Fourier map shows that the hexapeptide occupies the S1 subsite
predominantly and the standard recognition site constituted by Ser-132 to
Gly-136 and Gly-100 to Tyr-104 segments is virtually empty. The hexapeptide is
held firmly through a series of hydrogen bonds involving protein atoms and water
molecules. As a result of complex formation, Asp-39, His-69, Met-225, Ile-220,
Ser-219, Thr-223, and Ser-224 residues move appreciably to accommodate the
mercury atoms and the hexapeptide. The largest movement is observed for Met-225
which is involved in multiple interactions with both mercury and the
hexapeptide. The activity results indicate an inhibition rate of 95%, as a
result of the combined effect of mercury and hexapeptide.
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