Post-translational Maturation of Dystroglycan Is Necessary for Pikachurin Binding and Ribbon Synaptic Localization
Post-translational Maturation of Dystroglycan Is Necessary for Pikachurin Binding and Ribbon Synaptic Localization
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DOI：
10.1074/jbc.m110.116343
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发表时间：
2010-10-08
影响因子：
4.8
通讯作者：
Toda, Tatsushi
中科院分区：
文献类型：
--
作者：
Kanagawa, Motoi;Omori, Yoshihiro;Toda, Tatsushi
Pikachurin是最近发现的糖异常配体，在光感受器带突触的形成中起着至关重要的作用。众所周知，糖醛酸的糖基化对其配体结合活性是必要的，而糖基化与一组肌肉营养不良症有关，通常包括眼睛异常。由于对皮卡丘林和糖营养不良之间的相互作用及其对分子发病机制的影响知之甚少，因此我们在这里使用缺失构建体和糖基化缺陷肌营养不良小鼠模型（Large（myd）和pomgnt1缺陷小鼠）来表征相互作用。pikachurin - dysstroglycan结合是钙依赖性的，与其他dysstroglycan配体蛋白相比，对肝素和高NaCl浓度的抑制相对不敏感。利用pikachurin C末端层粘连蛋白球状结构域的缺失结构，我们发现由第二和第三层粘连蛋白球状结构域形成的一定的空间结构是pikachurin- dysstrodglycan相互作用所必需的。结合实验使用糖酐缺陷缺失构建体和来自大缺陷（大（myd））小鼠的组织样本表明，糖酐缺陷的大依赖修饰是皮卡丘林结合所必需的。此外，pikachurin与pomgnt1缺陷小鼠制备的糖醛酸失调蛋白的结合能力严重降低，表明o -甘露糖上glcnac - β 1,2分支的修饰也是相互作用的必要条件。免疫荧光分析揭示了这些模型动物的光感受器带突触中皮卡丘林定位的破坏。总之，我们的数据表明，由Large和POMGnT1介导的o -甘露糖的翻译后修饰对于皮卡丘林的结合和正确定位至关重要，并表明它们的破坏是肌营养不良患者眼睛异常的分子发病机制的基础。
Pikachurin, the most recently identified ligand of dystroglycan, plays a crucial role in the formation of the photoreceptor ribbon synapse. It is known that glycosylation of dystroglycan is necessary for its ligand binding activity, and hypoglycosylation is associated with a group of muscular dystrophies that often involve eye abnormalities. Because little is known about the interaction between pikachurin and dystroglycan and its impact on molecular pathogenesis, here we characterize the interaction using deletion constructs and mouse models of muscular dystrophies with glycosylation defects (Large(myd) and POMGnT1-deficient mice). Pikachurin-dystroglycan binding is calcium-dependent and relatively less sensitive to inhibition by heparin and high NaCl concentration, as compared with other dystroglycan ligand proteins. Using deletion constructs of the laminin globular domains in the pikachurin C terminus, we show that a certain steric structure formed by the second and the third laminin globular domains is necessary for the pikachurin-dystroglycan interaction. Binding assays using dystroglycan deletion constructs and tissue samples from Large-deficient (Large(myd)) mice show that Large-dependent modification of dystroglycan is necessary for pikachurin binding. In addition, the ability of pikachurin to bind to dystroglycan prepared from POMGnT1-deficient mice is severely reduced, suggesting that modification of the GlcNAc-beta 1,2-branch on O-mannose is also necessary for the interaction. Immunofluorescence analysis reveals a disruption of pikachurin localization in the photoreceptor ribbon synapse of these model animals. Together, our data demonstrate that post-translational modification on O-mannose, which is mediated by Large and POMGnT1, is essential for pikachurin binding and proper localization, and suggest that their disruption underlies the molecular pathogenesis of eye abnormalities in a group of muscular dystrophies.