Subramanian Shoba, Woolford Carol A, Jones Elizabeth W
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Mol Biol Cell. 2004 Jun;15(6):2593-605. doi: 10.1091/mbc.e03-10-0767. Epub 2004 Mar 26.
The Sec1/Munc18 (SM) family of proteins is thought to impart compartmental specificity to vesicle fusion reactions. Here we report characterization of Vps33p, an SM family member previously thought to act exclusively at the vacuolar membrane with the vacuolar syntaxin Vam3p. Vacuolar morphology of vps33Delta cells resembles that of cells lacking both Vam3p and the endosomal syntaxin Pep12p, suggesting that Vps33p may function with these syntaxins at the vacuole and the endosome. Consistent with this, vps33 mutants secrete the Golgi precursor form of the vacuolar hydrolase CPY into the medium. We also demonstrate that Vps33p acts at other steps, for vps33 mutants show severe defects in endocytosis at the late endosome. At the endosome, Vps33p and other class C members exist as a complex with Vps8p, a protein previously known to act in transport between the late Golgi and the endosome. Vps33p also interacts with Pep12p, a known interactor of the SM protein Vps45p. High copy PEP7/VAC1 suppresses vacuolar morphology defects of vps33 mutants. These findings demonstrate that Vps33p functions at multiple trafficking steps and is not limited to action at the vacuolar membrane. This is the first report demonstrating the involvement of a single syntaxin with two SM proteins at the same organelle.
Sec1/Munc18（SM）蛋白家族被认为赋予囊泡融合反应以区室特异性。在此，我们报告了Vps33p的特性，它是SM家族成员，此前被认为仅在液泡膜上与液泡 syntaxin Vam3p起作用。vps33Δ细胞的液泡形态类似于同时缺乏Vam3p和内体syntaxin Pep12p的细胞，这表明Vps33p可能在液泡和内体与这些syntaxin一起发挥作用。与此一致的是，vps33突变体将液泡水解酶CPY的高尔基体前体形式分泌到培养基中。我们还证明Vps33p在其他步骤起作用，因为vps33突变体在晚期内体的内吞作用中表现出严重缺陷。在内体中，Vps33p和其他C类成员与Vps8p形成复合物，Vps8p是一种先前已知在晚期高尔基体和内体之间的运输中起作用的蛋白质。Vps33p还与Pep12p相互作用，Pep12p是SM蛋白Vps45p的已知相互作用蛋白。高拷贝的PEP7/VAC1抑制vps33突变体的液泡形态缺陷。这些发现表明Vps33p在多个运输步骤中起作用，并不局限于在液泡膜上发挥作用。这是第一份证明单个syntaxin在同一细胞器中与两种SM蛋白相关的报告。
