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首页> 外文期刊>Biochemistry >CTP : Phosphocholine cytidylyltransferase binds anionic phospholipid vesicles in a cross-bridging mode
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CTP : Phosphocholine cytidylyltransferase binds anionic phospholipid vesicles in a cross-bridging mode

机译：CTP：磷脂酰胆碱转移酶以交叉桥结合方式结合阴离子磷脂囊泡

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摘要

CTP:phosphocholine cytidylyltransferase (CCT) catalyzes the rate-limiting step in phosphatidylcholine (PC) synthesis, and its activity is regulated by reversible association with membranes, mediated by an amphipathic helical domain M. Here we describe a new feature of the CCT alpha isoform, vesicle tethering. We show, using dynamic light scattering and transmission electron microscopy, that dimers of CCT alpha can cross-bridge separate vesicles to promote vesicle aggregation. The vesicles contained either class I activators (anionic phospholipids) or the less potent class II activators, which favor nonlamellar phase formation. CCT increased the apparent hydrodynamic radius and polydispersity of anionic phospholipid vesicles even at low CCT concentrations corresponding to only one or two dimers per vesicle. Electron micrographs of negatively stained phosphatidylglycerol (PG) vesicles confirmed CCT-mediated vesicle aggregation. CCT conjugated to colloidal gold accumulated on the vesicle surfaces and in areas of vesicle-vesicle contact. PG vesicle aggregation required both the membrane-binding domain and the intact CCT dimer, suggesting binding of CCT to apposed membranes via the two M domains situated on opposite sides of the dimerization domain. In contrast to the effects on anionic phospholipid vesicles, CCT did not induce aggregation of PC vesicles containing the class II lipids, oleic acid, diacylglycerol, or phosphatidylethanolamine. The different behavior of the two lipid classes reflected differences in measured binding affinity, with only strongly binding phospholipid vesicles being susceptible to CCT-induced aggregation. Our findings suggest a new model for CCT alpha domain organization and membrane interaction, and a potential involvement of the enzyme in cellular events that implicate close apposition of membranes.
机译：CTP：磷酸胆碱胞苷转移酶（CCT）催化磷脂酰胆碱（PC）合成中的限速步骤，其活性受两亲性螺旋结构域M介导的膜的可逆缔合调节。在这里，我们描述CCTα亚型的新特征，囊泡栓系。我们显示，使用动态光散射和透射电子显微镜，CCTα的二聚体可以跨桥分离囊泡，以促进囊泡聚集。囊泡包含I类活化剂（阴离子磷脂）或效力较弱的II类活化剂，它们有助于形成非层状相。即使在低CCT浓度下，CCT也增加了阴离子磷脂囊泡的表观流体力学半径和多分散性，每只囊泡仅含一个或两个二聚体。负染色的磷脂酰甘油（PG）囊泡的电子显微镜照片证实了CCT介导的囊泡聚集。 CCT与聚集在囊泡表面和囊泡与囊泡接触区域的胶体金结合。 PG囊泡聚集既需要膜结合结构域又需要完整的CCT二聚体，这表明CCT通过位于二聚结构域相对侧的两个M结构域与所结合的膜结合。与对阴离子磷脂囊泡的作用相反，CCT不会诱导含有II类脂质，油酸，二酰基甘油或磷脂酰乙醇胺的PC囊泡聚集。两种脂质类别的不同行为反映了测得的结合亲和力的差异，只有强结合的磷脂囊泡易受CCT诱导的聚集作用。我们的发现提出了一种CCTα结构域和膜相互作用的新模型，并且该酶可能参与细胞活动，这暗示了膜的紧密并置。

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