Effect of Arginine Loss in Myelin Basic Protein, as Occurs in Its Deiminated Charge Isoform, on Mediation of Actin Polymerization and Actin Binding to a Lipid Membrane in Vitro

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• 作者：Joan M. Boggs ; Godha Rangaraj ; Christopher M. D. Hill ; Ian R. Bates ; Yew-Meng Heng ; and George Harauz
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：March 8, 2005
• 年：2005
• 卷：44
• 期：9
• 页码：3524 - 3534
• 全文大小：359K
• 年卷期：v.44,no.9(March 8, 2005)
• ISSN：1520-4995

文摘

Myelin basic protein (MBP) binds to negatively charged lipids on the cytosolic surface ofoligodendrocyte membranes and is most likely responsible for adhesion of these surfaces in the multilayeredmyelin sheath. It can also polymerize actin, bundle F-actin filaments, and bind actin filaments to lipidbilayers through electrostatic interactions. MBP consists of a number of posttranslationally modifiedisoforms of varying charge, including C8, in which six arginines are deiminated to the uncharged residuecitrulline. The deiminated form decreases with development, but is increased in patients with thedemyelinating disease multiple sclerosis. Here we investigate the effect of decreased net positive chargeof MBP on its interaction with actin in vitro by comparing a recombinant murine form, rmC1, of themost highly charged unmodified isoform, C1, and a recombinant analogue of C8 in which six basic residuesare converted to glutamine, rmC8. The dissociation constant of the less charged isoform rmC8 for actinwas a little greater than that of rmC1, and rmC8 had somewhat reduced ability to polymerize actin andbundle F-actin filaments than rmC1. Moreover, rmC8 was more readily dissociated from actin by Ca²⁺-calmodulin than rmC1, and the ability of the deiminated isoform to bind actin to lipid bilayers was reduced.These results indicate that electrostatic forces are the primary determinant of the interaction of MBP withactin. The spin labeled side chains of a series of rmC1 and rmC8 variants containing single Cys substitutionsat seven sites throughout the sequence all became motionally restricted to a similar degree on bindingF-actin, indicating that the entire sequence is involved in interacting with actin filaments or is otherwisestructurally constrained in actin bundles. Thus, this posttranslational modification of MBP, which occursearly in life and is increased in multiple sclerosis, attenuates the ability of MBP to polymerize and bundleactin, and to bind it to a negatively charged membrane.