1l16
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(New page: 200px<br /><applet load="1l16" size="450" color="white" frame="true" align="right" spinBox="true" caption="1l16, resolution 1.7Å" /> '''STRUCTURAL ANALYSIS O...)
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Revision as of 18:02, 20 November 2007
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STRUCTURAL ANALYSIS OF THE TEMPERATURE-SENSITIVE MUTANT OF BACTERIOPHAGE T4 LYSOZYME, GLYCINE 156 (RIGHT ARROW) ASPARTIC ACID
Overview
The structure of the mutant of bacteriophage T4 lysozyme in which Gly-156, is replaced by aspartic acid is described. The lysozyme was isolated by, screening for temperature-sensitive mutants and has a melting temperature, at pH 6.5 that is 6.1 degrees C lower than wild type. The mutant structure, is destabilized, in part, because Gly-156 has conformational angles (phi, psi) that are not optimal for a residue with a beta-carbon. High, resolution crystallographic refinement of the mutant structure (R = 17.7%, at 1.7 A resolution) shows that the Gly----Asp substitution does not, significantly alter the configurational angles (phi, psi) but forces the, backbone to move, as a whole, approximately 0.6 A away from its position, in wild-type lysozyme. This induced strain weakens a hydrogen bond network, that exists in the wild-type structure and also contributes to the reduced, stability of the mutant lysozyme. The introduction of an acidic side chain, reduces the overall charge on the molecule and thereby tends to increase, the stability of the mutant structure relative to wild type. However, at, neutral pH this generalized electrostatic stabilization is offset by, specific electrostatic repulsion between Asp-156 and Asp-92. The activity, of the mutant lysozyme is approximately 50% that of wild-type lysozyme., This reduction in activity might be due to introduction of a negative, charge and/or perturbation of the surface of the molecule in the region, that is assumed to interact with peptidoglycan substrates.
About this Structure
1L16 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 analysis of the temperature-sensitive mutant of bacteriophage T4 lysozyme, glycine 156----aspartic acid., Gray TM, Matthews BW, J Biol Chem. 1987 Dec 15;262(35):16858-64. PMID:3680274
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