1eq5

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spinqualitylabelsall models 1eq5, resolution 1.8Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

CRYSTAL STRUCTURES OF SALT BRIDGE MUTANTS OF HUMAN LYSOZYME

Contents 1 Overview 2 Disease 3 About this Structure 4 Reference

Overview

Salt bridges play important roles in the conformational stability of, proteins. However, the effect of a surface salt bridge on the stability, remains controversial even today; some reports have shown little, contribution of a surface salt bridge to stability, whereas others have, shown a favorable contribution. In this study, to elucidate the net, contribution of a surface salt bridge to the conformational stability of a, protein, systematic mutant human lysozymes, containing one Glu to Gln, (E7Q) and five Asp to Asn mutations (D18N, D49N, D67N, D102N, and D120N), at residues where a salt bridge is formed near the surface in the, wild-type structure, were examined. The thermodynamic parameters for, denaturation between pH 2.0 and 4.8 were determined by use of a, differential scanning calorimeter, and the crystal structures were, analyzed by X-ray crystallography. The denaturation Gibbs energy (DeltaG), of all mutant proteins was lower than that of the wild-type protein at pH, 4, whereas there was little difference between them near pH 2. This is, caused by the fact that the Glu and Asp residues are ionized at pH 4 but, protonated at pH 2, indicating a favorable contribution of salt bridges to, the wild-type structure at pH 4. Each contribution was not equivalent, but, we found that the contributions correlate with the solvent inaccessibility, of the salt bridges; the salt bridge contribution was small when 100%, accessible, while it was about 9 kJ/mol if 100% inaccessible. This, conclusion indicates how to reconcile a number of conflicting reports, about role of surface salt bridges in protein stability. Furthermore, the, effect of salts on surface salt bridges was also examined. In the presence, of 0.2 M KCl, the stability at pH 4 decreased, and the differences in, stability between the wild-type and mutant proteins were smaller than, those in the absence of salts, indicating the compensation to the, contribution of salt bridges with salts. Salt bridges with more than 50%, accessibility did not contribute to the stability in the presence of 0.2 M, KCl.

Disease

Known diseases associated with this structure: Amyloidosis, renal OMIM:[153450], Microphthalmia, syndromic 1 OMIM:[309800]

About this Structure

1EQ5 is a Single protein structure of sequence from Homo sapiens with NA as ligand. Active as Lysozyme, with EC number 3.2.1.17 Full crystallographic information is available from OCA.

Reference

Contribution of salt bridges near the surface of a protein to the conformational stability., Takano K, Tsuchimori K, Yamagata Y, Yutani K, Biochemistry. 2000 Oct 10;39(40):12375-81. PMID:11015217

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