1ahr

From Proteopedia

Revision as of 08:44, 20 November 2007

CALMODULIN MUTANT WITH A TWO RESIDUE DELETION IN THE CENTRAL HELIX

Overview

BACKGROUND: Calmodulin (CaM) is the major calcium-dependent regulator of a, large variety of important intracellular processes in eukaryotes. The, structure of CaM consists of two globular calcium-binding domains joined, by a central 28-residue alpha helix. This linker helix has been, hypothesized to act as a flexible tether and is crucial for the binding, and activation of numerous target proteins. Although the way in which, alterations of the central helix modulate the molecular recognition, mechanism is not known exactly, the relative orientation of the globular, domains seems to be of great importance. The structural analysis of, central helix mutants may contribute to a better understanding of how, changes in the conformation of CaM effect its function. RESULTS: We have, determined the crystal structure of a calcium-saturated mutant of chicken, CaM (mut-2) that lacks two residues in the central helix, Thr79 and Asp80, at 1.8 A resolution. The mutated shorter central helix is straight, relative to that of the wild-type structure. The loss of a partial turn of, the central alpha helix causes the C-terminal domain to rotate 220 degrees, around the helix axis, with respect to the N-terminal domain. This, rotation places the two domains on the same side of the central helix, in, a cis orientation, rather than in the trans orientation found in wild-type, structures. CONCLUSIONS: The deletion of two residues in the central helix, of CaM does not distort or cause a bending of the linker alpha helix. The, main consequence of the mutation is a change in the relative orientation, of the two globular calcium-binding domains, causing the hydrophobic, patches in these domains to be closer and much less accessible to interact, with the target enzymes. This may explain why this mutant of CaM shows a, marked decrease in its ability to activate some enzymes while the mutation, has little or no effect on its ability to activate others.

About this Structure

1AHR is a Single protein structure of sequence from Gallus gallus with CA as ligand. Full crystallographic information is available from OCA.

Reference

The structure of a calmodulin mutant with a deletion in the central helix: implications for molecular recognition and protein binding., Tabernero L, Taylor DA, Chandross RJ, VanBerkum MF, Means AR, Quiocho FA, Sack JS, Structure. 1997 May 15;5(5):613-22. PMID:9195880

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