218l

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spinqualitylabelsall models 218l, resolution 2.05Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

PROTEIN STRUCTURE PLASTICITY EXEMPLIFIED BY INSERTION AND DELETION MUTANTS IN T4 LYSOZYME

Overview

To further investigate the ways in which proteins respond to changes in, the length of the polypeptide chain, a series of 32 insertions and five, deletions were made within nine different alpha-helices of T4 lysozyme. In, most cases, the inserted amino acid was a single alanine, although in some, instances up to four residues, not necessarily alanine, were used., Different insertions destabilized the protein by different amounts, ranging from approximately 1 to 6 kcal/mol. In one case, no protein could, be obtained. An "extension" mutant in which the carboxy terminus of the, molecule was extended by four alanines increased stability by 0.3, kcal/mol. For the deletions, the loss in stability ranged from, approximately 3 to 5 kcal/mol. The structures of six insertion mutants, as, well as one deletion mutant and the extension mutant, were determined, three in crystal forms nonisomorphous with wild type. In all cases, including previously described insertion mutants within a single, alpha-helix, there appears to be a strong tendency to preserve the helix, by translocating residues so that the effects of the insertion are, propagated into a bend or loop at one end or the other of the helix. In, three mutants, even the hydrophobic core was disrupted so as to permit the, preservation of the alpha-helix containing the insertion. Translocation, (or "register shift") was also observed for the deletion mutant, in this, case a loop at the end of the helix being shortened. In general, when, translocation occurs, the reduction in stability is only moderate, averaging 2.5 kcal/mol. Only in the most extreme cases does "bulging" or, "looping-out" occur within the body of an alpha-helix, in which case the, destabilization is substantial, averaging 4.9 kcal/mol. Looping-out can, occur for insertions close to the end of a helix, in which case the, destabilization is less severe, averaging 2.6 kcal/mol. Mutant A73-[AAA], as well as mutants R119-[A] and V131-[A], include shifts in the backbone, of 3-6 A, extending over 20 residues or more. As a result, residues, 114-142, which form a "cap" on the carboxy-terminal domain, undergo, substantial reorganizations such that the interface between this "cap" and, the rest of the protein is altered substantially. In the case of mutant, A73-[AAA], two nearby alpha-helices, which form a bend of approximately, 105 degrees in the wild-type structure, reorganize in the mutant structure, to form a single, essentially straight helix. These structural responses, to mutation demonstrate the plasticity of protein structures and, illustrate ways in which their three-dimensional structures might changes, during evolution.

About this Structure

218L 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

Protein structural plasticity exemplified by insertion and deletion mutants in T4 lysozyme., Vetter IR, Baase WA, Heinz DW, Xiong JP, Snow S, Matthews BW, Protein Sci. 1996 Dec;5(12):2399-415. PMID:8976549

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