UNSPECIFIED (1999) Evidence of noncovalent dimerization of calmodulin. EUROPEAN JOURNAL OF BIOCHEMISTRY, 261 (1). pp. 337-344. ISSN 0014-2956

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Abstract

Calcium-binding proteins, such as S-100, dimerize readily, and this phenomenon plays an important role in their regulation of target enzymes [Krebs, J., Quadroni, M. & Van Eldik, L,J. (1995) Nat. Struct. Biol. 2, 711-714; Kilby, P.M., Van Eldik, L.J. & Roberts, G.C. (1996) Structure 4, 1041-1052]. We have investigated by Fourier-transform ion cyclotron resonance (FTICR) MS the conformational stares of the calcium-binding protein calmodulin, and present clear evidence for a calmodulin dimer formed as a result of noncovalent interactions between folded monomers. Ultra-high-resolution electrospray ionization (ESI) mass spectra for calmodulin, obtained with a 9.4 T FTICR mass spectrometer, are presented. With the use of denaturing solutions (1 : 1 acetonitrile/water + 1% formic acid), relatively high charge states (20 < z < 10) of monomeric calmodulin ions were detected, whereas when calmodulin was electrosprayed from buffer, monomers ions with only 5-10 charges were detected. CD measurements for calmodulin in buffered solution revealed that its alpha-helical content was significantly higher than that for calmodulin in acetonitrile/water solutions, consistent with a proposition that changes in charge state distributions observed in the MS experiments reflect differing states of calmodulin folding. Under buffered conditions, noncovalently bound calmodulin dimers were observed by ESI FTICR MS. Analytical ultracentrifugation experiments carried out in the same solution conditions as those used in the MS experiments were consistent with the proposed calmodulin dimer-monomer equilibrium. The ultra-high mass resolution achieved with the 9.4 T FTICR mass spectrometer allowed unequivocal identification of the noncovalent, as opposed to covalent, character of the calmodulin dimer.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Journal or Publication Title:	EUROPEAN JOURNAL OF BIOCHEMISTRY
Publisher:	BLACKWELL SCIENCE LTD
ISSN:	0014-2956
Date:	April 1999
Volume:	261
Number:	1
Number of Pages:	8
Page Range:	pp. 337-344
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/14658

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