1l51
From Proteopedia
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STRUCTURAL AND THERMODYNAMIC ANALYSIS OF THE PACKING OF TWO ALPHA-HELICES IN BACTERIOPHAGE T4 LYSOZYME
Overview
Packing interactions in bacteriophage T4 lysozyme were explored by, determining the structural and thermodynamic effects of substitutions for, Ala98 and neighboring residues. Ala98 is buried in the core of T4 lysozyme, in the interface between two alpha-helices. The Ala98 to Val (A98V), replacement is a temperature-sensitive lesion that lowers the denaturation, temperature of the protein by 15 degrees C (pH 3.0, delta delta G = -4.9, kcal/mol) and causes atoms within the two helices to move apart by up to, 0.7 A. Additional structural shifts also occur throughout the C-terminal, domain. In an attempt to compensate for the A98V replacement, substitutions were made for Val149 and Thr152, which make contact with, residue 98. Site-directed mutagenesis was used to construct the multiple, mutants A98V/T152S, A98V/V149C/T152S and the control mutants T152S, V149C, and A98V/V149I/T152S. These proteins were crystallized, and their, high-resolution X-ray crystal structures were determined. None of the, second-site substitutions completely alleviates the destabilization or the, structural changes caused by A98V. The changes in stability caused by the, different mutations are not additive, reflecting both direct interactions, between the sites and structural differences among the mutants. As an, example, when Thr152 in wild-type lysozyme is replaced with serine, the, protein is destabilized by 2.6 kcal/mol. Except for a small movement of, Val94 toward the cavity created by removal of the methyl group, the, structure of the T152S mutant is very similar to wild-type T4 lysozyme. In, contrast, the same Thr152 to Ser replacement in the A98V background causes, almost no change in stability. Although the structure of A98V/T152S, remains similar to A98V, the combination of T152S with A98V allows, relaxation of some of the strain introduced by the Ala98 to Val, replacement. These studies show that removal of methyl groups by mutation, can be stabilizing (Val98----Ala), neutral (Thr152----Ser in A98V) or, destabilizing (Val149----Cys, Thr152----Ser). Such diverse thermodynamic, effects are not accounted for by changes in buried surface area or free, energies of transfer of wild-type and mutant side-chains. In general, the, changes in protein stability caused by a mutation depend not only on, changes in the free energy of transfer associated with the substitution, but also on the structural context within which the mutation occurs and on, the ability of the surrounding structure to relax in response to the, substitution.(ABSTRACT TRUNCATED AT 400 WORDS)
About this Structure
1L51 is a Single protein structure of sequence from Bacteriophage t4. Active as Lysozyme, with EC number 3.2.1.17 Full crystallographic information is available from OCA.
Reference
Structural and thermodynamic analysis of the packing of two alpha-helices in bacteriophage T4 lysozyme., Daopin S, Alber T, Baase WA, Wozniak JA, Matthews BW, J Mol Biol. 1991 Sep 20;221(2):647-67. PMID:1920439
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