Effect of phosphorylation of myelin basic protein by MAPK on its interactions with actin and actin binding to a lipid membrane in vitro
Effect of phosphorylation of myelin basic protein by MAPK on its interactions with actin and actin binding to a lipid membrane in vitro
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DOI：
10.1021/bi0519194
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发表时间：
2006-01-17
期刊：
影响因子：
2.9
通讯作者：
Heng, YM
中科院分区：
文献类型：
--
作者：
Boggs, JM;Rangaraj, G;Heng, YM
髓鞘碱性蛋白(MBP)与少突胶质细胞膜胞浆表面的带负电荷的脂类结合，很可能是这些表面在多层髓鞘中黏附的原因。它还可以聚合肌动蛋白，捆绑F-肌动蛋白细丝，并通过静电相互作用将肌动蛋白细丝结合到脂质双层上。MBP由许多不同电荷的翻译后修饰的异构体组成，其中一些是由不同的激酶在几个位置上的磷酸化而产生的，包括丝裂原激活的蛋白激酶(MAPK)。MBP在少突胶质细胞中的磷酸化是对各种细胞外刺激的反应。MBP的磷酸化/去磷酸化也发生在髓鞘中，以响应大脑中的电活动。在这里，我们研究了MBP的磷酸化对其与肌动蛋白相互作用的影响，方法是用MAPK在两个位点上磷酸化最高电荷的未修饰异构体C1。磷酸化降低了MBP聚合肌动蛋白和捆绑肌动蛋白细丝的能力，但不影响MBP-肌动蛋白复合体的解离常数或钙-钙调蛋白解离复合体的能力。磷酸化对MBP-肌动蛋白复合体最显著的影响是它与带负电荷的脂双层结合的能力显著降低。这种影响远大于早先报道的MBP的另一种电荷异构体C8，在C8中，6个精氨酸被脱亚胺为瓜氨酸，导致净正电荷减少6。这些结果表明，尽管平均静电力是MBP与肌动蛋白相互作用的主要决定因素，但磷酸化可能由于特定部位的静电效应或构象变化而产生额外的影响。因此，MBP的磷酸化是对髓鞘和少突胶质细胞中各种细胞外信号的反应，削弱了MBP聚合和捆绑肌动蛋白并将其结合到带负电的膜上的能力。
Myelin basic protein (MBP) binds to negatively charged lipids on the cytosolic surface of oligodendrocyte membranes and is most likely responsible for adhesion of these surfaces in the multilayered myelin sheath. It can also polymerize actin, bundle F-actin filaments, and bind actin filaments to lipid bilayers through electrostatic interactions. MBP consists of a number of posttranslationally modified isomers of varying charge, some resulting from phosphorylation at several sites by different kinases, including mitogen-activated protein kinase (MAPK). Phosphorylation of MBP in oligodendrocytes occurs in response to various extracellular stimuli. Phosphorylation/dephosphorylation of MBP also occurs in the myelin sheath in response to electrical activity in the brain. Here we investigate the effect of phosphorylation of MBP on its interaction with actin in vitro by phosphorylating the most highly charged unmodified isomer, C1, at two sites with MAPK. Phosphorylation decreased the ability of MBP to polymerize actin and to bundle actin filaments but had no effect on the dissociation constant of the MBP-actin complex or on the ability of Ca2+-calmodulin to dissociate the complex. The most significant effect of phosphorylation on the MBP-actin complex was a dramatic reduction in its ability to bind to negatively charged lipid bilayers. The effect was much greater than that reported earlier for another charge isomer of MBP, C8, in which six arginines were deiminated to citrulline, resulting in a reduction of net positive charge of 6. These results indicate that although average electrostatic forces are the primary determinant of the interaction of MBP with actin, phosphorylation may have an additional effect due to a site-specific electrostatic effect or to a conformational change. Thus, phosphorylation of MBP, which occurs in response to various extracellular signals in both myelin and oligodendrocytes, attenuates the ability of MBP to polymerize and bundle actin and to bind it to a negatively charged membrane.