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PDBsum entry 1lyh
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Hydrolase(o-glycosyl)
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PDB id
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1lyh
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References listed in PDB file
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Key reference
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Title
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Dissection of helix capping in t4 lysozyme by structural and thermodynamic analysis of six amino acid substitutions at thr 59.
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Authors
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J.A.Bell,
W.J.Becktel,
U.Sauer,
W.A.Baase,
B.W.Matthews.
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Ref.
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Biochemistry, 1992,
31,
3590-3596.
[DOI no: ]
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PubMed id
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Abstract
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Threonine 59, a helix-capping residue at the amino terminus of the longest helix
in T4 phage lysozyme, was substituted with valine, alanine, glycine, serine,
asparagine, and aspartic acid. The valine, alanine, and glycine replacements
were observed to be somewhat more destabilizing than serine, asparagine, and
aspartic acid. The crystal structures of the different variants showed that
changes in conformation occurred at the site of substitution, including Asp 61,
which is nearby, as well as displacement of a solvent molecule that is
hydrogen-bonded to the gamma-oxygen of Thr 59 in wild-type lysozyme. Neither the
structures nor the stabilities of the mutant proteins support the hypothesis of
Serrano and Fersht (1989) that glycine and alanine are better helix-capping
residues than valine because a smaller-sized residue allows better hydration at
the end of the helix. In the aspartic acid and asparagine replacements the
substituted side chains form hydrogen bonds with the end of the helix, as does
threonine and serine at this position. In contrast, however, the Asp and Asn
side chains also make unusually close contacts with carbon atoms in Asp 61. This
suggests a structural basis for the heretofore puzzling observations that
asparagine is more frequently observed as a helix-capping residue than threonine
[Richardson, J. S., & Richardson, D. C. (1988) Science 240, 1648-1652] yet
Thr----Asn replacements at N-cap positions in barnase were found to be
destabilizing [Serrano, L., & Fersht, A. R. (1989) Nature 342,
296-299].(ABSTRACT TRUNCATED AT 250 WORDS)
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