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PDBsum entry 1l77
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Hydrolase (o-glycosyl)
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PDB id
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1l77
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References listed in PDB file
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Key reference
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Title
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Design and structural analysis of alternative hydrophobic core packing arrangements in bacteriophage t4 lysozyme.
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Authors
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J.H.Hurley,
W.A.Baase,
B.W.Matthews.
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Ref.
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J Mol Biol, 1992,
224,
1143-1159.
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PubMed id
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Abstract
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An attempt has been made to design modified core-packing arrangements in
bacteriophage T4 lysozyme. Alternative replacements of the buried residues
Leu99, Met102, Val111 and Phe153 were selected using packing calculations and
energy minimization. To test the design procedure, a series of multiple mutants
was constructed culminating in the replacement L99F/M102L/V111I/F153L. These
variants decrease the stability of T4 lysozyme by approximately 0 to 2 kcal/mol.
The crystal structures of a number of the variants were determined. In the
variant in which Val111 was replaced by Ile, alpha-helix 107-114 moved by
approximately 1.5 A, breaking the hydrogen bond between the backbone carbonyl
group of Thr109 and the backbone amide group of Gly113. This conformational
change was not anticipated by the design procedure. Compensating interactions of
magnitude up to 1.1 kcal/mol occur for some sets of mutations, while other sets
display nearly additive stability changes. Within experimental error, the
stability of the double mutant V111F/F153L is additive, with delta delta G
different by only 0.1 kcal/mol from the sum of the two single mutants. The
quadruple mutant L99F/M102L/V111I/F153L is destabilized by 0.5 kcal/mol,
compared to delta delta G = -1.6 kcal/mol for the sum of the four single
mutants. Multiple mutants show smaller overall structural changes from wild-type
than M102L or V111I alone. Co-operative changes in structure and stability can
be rationalized in terms of specific structural differences between single and
multiple mutants. Genuine repacking of the hydrophobic core of T4 lysozyme with
minimal effects on structure, stability and activity thus appears to have been
achieved.
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