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    The effect of calcium ions and peptide ligands on the relative stabilities of the Calmodulin Dumbbell and compact structures

    Wyttenbach, T. and Grabenauer, M. and Thalassinos, Konstantinos and Scrivens, J.H. and Bowers, M.T. (2010) The effect of calcium ions and peptide ligands on the relative stabilities of the Calmodulin Dumbbell and compact structures. The Journal of Physical Chemistry B 114 (1), pp. 437-447. ISSN 1520-6106.

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    Abstract

    A combination of ion mobility and mass spectrometry methods was used to characterize the molecular shape of the protein calmodulin (CaM) and its complexes with calcium and a number of peptide ligands. CaM, a calcium-binding protein composed of 148 amino acid residues, was found by X-ray crystallography to occur both in a globular shape and in the shape of an extended dumbbell. Here, it was found, as solutions of CaM and CaM complexes were sprayed into the solvent-free environment of the mass spectrometer, that major structural features of the molecule and the stoichiometry of the units constituting a complex in solution were preserved in the desolvation process. Two types of CaM structures were observed in our experiments: a compact and an extended form of CaM with measured cross sections in near-perfect agreement with those calculated for the known globular and extended dumbbell X-ray geometries. Calcium-free solutions yielded predominantly an extended CaM conformation. Can2+−CaM complexes were observed in calcium-containing solutions, n = 0−4, with the population of the compact conformation increasing relative to the elongated conformation as n increases. For n = 4, a predominantly compact globular conformation was observed. Solutions containing the peptide CaMKII290−309, the CaM target domain of the Ca2+/calmodulin-dependent protein kinase II (CaMKII) enzyme, yielded predominantly globular Ca42+−CaM−CaMKII290−309 complexes. Similar results were obtained with the 26-residue peptide melittin. For the 14-residue C-terminal melittin fragment, on the other hand, formation of both a 1:1 and a 1:2 CaM−peptide complex was detected. On the basis of the entirety of our results, we conclude that the collapse of extended (dumbbell-like) CaM structures into more compact globular structures occurs upon specific binding of four calcium ions. Furthermore, this calcium-induced structural collapse of CaM appears to be a prerequisite for formation of a particularly stable CaM−peptide complex involving peptides long enough to be engaged in interactions with both lobes of CaM.

    Metadata

    Item Type: Article
    School: School of Science > Biological Sciences
    Research Centres and Institutes: Structural Molecular Biology, Institute of (ISMB)
    Depositing User: Administrator
    Date Deposited: 20 May 2013 11:43
    Last Modified: 06 Dec 2016 10:40
    URI: https://eprints.bbk.ac.uk/id/eprint/6896

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