Sun Ning, Critchley David R, Paulin Denise, Li Zhenlin, Robson Richard M
Muscle Biology Group, Department of Biochemistry, Biophysics and Molecular Biology and of Animal Science, Iowa State University, Ames, IA 50011-3260, USA.
Biochem J. 2008 Feb 1;409(3):657-67. doi: 10.1042/BJ20071188.
Synemin is a very large, unique member of the IF (intermediate filament) protein superfamily. Association of synemin with the major IF proteins, desmin and/or vimentin, within muscle cells forms heteropolymeric IFs. We have previously identified interactions of avian synemin with alpha-actinin and vinculin. Avian synemin, however, is expressed as only one form, whereas human synemin is expressed as two major splice variants, namely alpha- and beta-synemins. The larger alpha-synemin contains an additional 312-amino-acid insert (termed SNTIII) located near the end of the long C-terminal tail domain. Whether alpha- and beta-synemins have different cellular functions is unclear. In the present study we show, by in vitro protein-protein interaction assays, that SNTIII interacts directly with both vinculin and metavinculin. Furthermore, SNTIII interacts with vinculin in vivo, and this association is promoted by PtdIns(4,5)P(2). SNTIII also specifically co-localizes with vinculin within focal adhesions when transiently expressed in mammalian cells. In contrast, other regions of synemin show distinct localization patterns in comparison with those of SNTIII, without labelling focal adhesions. Our results indicate that alpha-synemin, but not beta-synemin, interacts with both vinculin and metavinculin, thereby linking the heteropolymeric IFs to adhesion-type junctions, such as the costameres located within human striated muscle cells.
联丝蛋白是中间丝（IF）蛋白超家族中一个非常大的独特成员。在肌肉细胞内，联丝蛋白与主要的中间丝蛋白结蛋白和/或波形蛋白结合形成异聚中间丝。我们之前已鉴定出禽联丝蛋白与α-辅肌动蛋白和纽蛋白之间的相互作用。然而，禽联丝蛋白仅以一种形式表达，而人联丝蛋白以两种主要的剪接变体形式表达，即α-联丝蛋白和β-联丝蛋白。较大的α-联丝蛋白在长的C末端尾部结构域末端附近含有一个额外的312个氨基酸的插入片段（称为SNTIII）。α-联丝蛋白和β-联丝蛋白是否具有不同的细胞功能尚不清楚。在本研究中，我们通过体外蛋白质-蛋白质相互作用分析表明，SNTIII直接与纽蛋白和变纽蛋白相互作用。此外，SNTIII在体内与纽蛋白相互作用，并且这种结合由磷脂酰肌醇-4,5-二磷酸（PtdIns(4,5)P(2)）促进。当在哺乳动物细胞中瞬时表达时，SNTIII也在粘着斑内与纽蛋白特异性共定位。相比之下，联丝蛋白的其他区域与SNTIII的定位模式不同，不标记粘着斑。我们的结果表明，α-联丝蛋白而非β-联丝蛋白与纽蛋白和变纽蛋白都相互作用，从而将异聚中间丝与粘附型连接（如位于人横纹肌细胞内的肌小节）相连。
