Volchuk A, Mitsumoto Y, He L, Liu Z, Habermann E, Trimble W, Klip A
Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
Biochem J. 1994 Nov 15;304 ( Pt 1)(Pt 1):139-45. doi: 10.1042/bj3040139.
Molecular studies have identified a family of synaptic vesicle-associated membrane proteins (VAMPs, also known as synaptobrevins) which have been implicated in synaptic vesicle docking and/or fusion with plasma membrane proteins. Here we demonstrate the expression of two members of this family, VAMP-2/synaptobrevin II and cellubrevin, in skeletal muscle, a tissue with both constitutive and regulated membrane traffic. The 18 kDa VAMP-2 polypeptide was detected in purified membrane fractions from adult skeletal muscle and from L6 myotubes in culture, demonstrating that the presence of this protein in the isolated muscle membrane fractions is not the result of contamination by ancillary tissues such as peripheral nerve. Furthermore, skeletal muscle and the muscle cell line also expressed cellubrevin, a VAMP-2 homologue of 17 kDa; which is much less abundant in brain cells. Both VAMP-2 and cellubrevin were preferentially isolated in membrane fractions rich in plasma membranes, and were less concentrated in light microsomes and other internal membrane fractions of mature muscle or muscle cells in culture. Interestingly, both VAMP-2 and cellubrevin were much more abundant in the differentiated L6 myotubes than in their precursor myoblasts, suggesting that they are required for functions of differentiated muscle cells. The identity of both polypeptides was further confirmed by their susceptibility to proteolysis by Clostridium tetanus toxin. Expression of these products was further established by the presence of mRNA transcripts of VAMP-2 and cellubrevin, but not of VAMP-1, in both skeletal muscle and L6 myotubes. In contrast, other synaptic vesicle and docking/fusion components were undetectable, such as VAMP-1, SNAP25 and syntaxin 1A/1B, as were synaptophysin and synapsin Ia/Ib, proteins which are believed to be involved in sensing the signal for neuronal exocytosis. It is concluded that VAMP-2 and cellubrevin are expressed in skeletal muscle cells and may each participate in specific processes of intracellular membrane traffic.
分子研究已鉴定出一类突触小泡相关膜蛋白（VAMPs，也称为突触融合蛋白），它们与突触小泡对接和/或与质膜蛋白融合有关。在此，我们证明了该家族的两个成员，VAMP - 2/突触融合蛋白II和细胞ubrevin，在骨骼肌中的表达，骨骼肌是一个具有组成性和调节性膜运输的组织。在成年骨骼肌和培养的L6肌管的纯化膜组分中检测到18 kDa的VAMP - 2多肽，这表明该蛋白在分离的肌膜组分中的存在不是诸如外周神经等附属组织污染的结果。此外，骨骼肌和肌肉细胞系也表达细胞ubrevin，一种17 kDa的VAMP - 2同源物；其在脑细胞中的含量要少得多。VAMP - 2和细胞ubrevin都优先在富含质膜的膜组分中分离出来，并且在成熟肌肉或培养的肌肉细胞的轻微粒体和其他内膜组分中的浓度较低。有趣的是，VAMP - 2和细胞ubrevin在分化的L6肌管中比在其前体成肌细胞中丰富得多，这表明它们是分化的肌肉细胞功能所必需的。两种多肽的身份通过它们对破伤风梭菌毒素蛋白水解的敏感性进一步得到证实。通过在骨骼肌和L6肌管中存在VAMP - 2和细胞ubrevin的mRNA转录本，但不存在VAMP - 1的mRNA转录本，进一步确定了这些产物的表达。相比之下，其他突触小泡和对接/融合组分无法检测到，如VAMP - 1、SNAP25和 syntaxin 1A/1B，以及突触素和突触结合蛋白Ia/Ib，这些蛋白被认为参与感知神经元胞吐作用的信号。结论是，VAMP - 2和细胞ubrevin在骨骼肌细胞中表达，并且可能各自参与细胞内膜运输的特定过程。
