A novel alternatively spliced variant of synaptotagmin VI lacking a transmembrane domain - Implications for distinct functions of the two isoforms
A novel alternatively spliced variant of synaptotagmin VI lacking a transmembrane domain - Implications for distinct functions of the two isoforms
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DOI：
10.1074/jbc.274.44.31428
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发表时间：
1999-10-29
影响因子：
4.8
通讯作者：
Mikoshiba, K
中科院分区：
文献类型：
--
作者：
Fukuda, M;Mikoshiba, K
突触结合蛋白是一个膜蛋白家族，其特征在于单个跨膜区和串联C2结构域，并且可能调节组成型和/或受调节的囊泡运输。我们已经表明，突触结合蛋白的一个亚类（III、V、VI和X）通过在其N末端的进化上保守的半胱氨酸基序形成同源和异源二聚体（Fukuda，M.，Kanno，E.，和Mikoshiba，K.（1999）J.Biol.Chem.274，31421-31427）。在该研究中，我们鉴定了突触结合蛋白（Syt）VI的新的可变剪接变体，其缺少包括跨膜区的N-末端85个氨基酸（因此命名为Syt VI Delta TM）。因为它缺乏负责自我二聚化的半胱氨酸基序，Syt VI Delta TM即使在Ca 2+存在下也不能与Syt VI结合。尽管缺乏跨膜区，Syt VI Delta TM可以通过C-末端29个氨基酸与质膜结合。在成年小鼠脑中，用抗Syt VI抗体检测到两条M-r接近50，000的密切共迁移带，其与重组Syt VI Delta TM的分子量密切对应。这些免疫反应条带在小鼠脑的可溶性组分和膜组分中都有发现，表明它们是膜相关蛋白在PC 12或COS-7细胞中Syt VI和Syt VI Delta TM的表达表明这两种分子具有不同的亚细胞分布：是存在于胞质溶胶中或与质膜或内部膜结构，而Syt M是本地化的内质网和/或高尔基体样核周区室，这些结果表明，Syt VI和Syt VI Delta TM可能在囊泡运输中发挥不同的作用。
Synaptotagmins are a family of membrane proteins that are characterized by a single transmembrane region and tandem C2 domains and that are likely to regulate constitutive and/or regulated vesicle traffic, We have shown that a subclass of synaptotagmins (III, V,VI, and X) forms homo- and heterodimers through an evolutionarily conserved cysteine motif at their N termini (Fukuda, M., Kanno, E., and Mikoshiba, K. (1999) J. Biol. Chem. 274, 31421-31427), In this study, we identified a novel alternatively spliced variant of synaptotagmin (Syt) VI that lacks the N-terminal 85 amino acids including the transmembrane region (thus designated as Syt VI Delta TM). Because it lacks the cysteine motif responsible for self-dimerization, Syt VI Delta TM could not associate with Syt VI even in the presence of Ca2+. Despite lacking the transmembrane region, Syt VI Delta TM can associate with the plasma membrane through the C-terminal 29 amino acids. In adult mouse brain, two closely comigrating bands at M-r similar to 50,000, which closely corresponded to the molecular weight of recombinant Syt VI Delta TM, were detected by anti-Syt VI antibody. These immunoreactive bands were found in both soluble and membrane fractions of mouse brain, indicating that they are membrane-associated proteins (Syt VI Delta TM), but not transmembrane proteins (Syt VI), Expression of Syt VI and Syt VI Delta TM in PC12 or COS-7 cells indicated that the two molecules have a distinct subcellular distribution: Syt VI Delta TM: is present in the cytosol or is associated with the plasma membrane or internal membrane structures, whereas Syt M is localized to the endoplasmic reticulum and/or Golgi-like perinuclear compartment, These results suggest that Syt VI and Syt VI Delta TM may play distinct roles in vesicular trafficking.