The HOPS/class C Vps complex tethers membranes by binding to one Rab GTPase in each apposed membrane.
The HOPS/class C Vps complex tethers membranes by binding to one Rab GTPase in each apposed membrane.
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DOI：
10.1091/mbc.e14-04-0922
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发表时间：
2015-07-15
影响因子：
3.3
通讯作者：
Stroupe C
中科院分区：
文献类型：
--
作者：
Ho R;Stroupe C
HOPS/C类VPS复合体是酵母空泡Rab GTP酶Ypt7p的效应器，通过与每个相对的膜上的Rab GTP酶结合来连接低曲率膜。这是第一次确定与不同膜的相互作用导致Rab效应器依赖的膜系留。许多Rab GTPase效应器是膜系留因子，即在细胞内膜融合之前，它们物理连接两个相对的膜。在这项研究中，我们调查了不同的结合因子需要在相对的膜上的Rab效应依赖的系链。我们发现，只有当酵母空泡Rab GTP酶Ypt7p存在于两个被系膜中时，同型融合和蛋白质分选/C类空泡蛋白分选(HOPS/C类VPS)复合体才能系住低曲率膜，即直径为∼100 nm的脂质体。当啤酒花被空泡酪蛋白激酶I，Yck 3p磷酸化时，只有当GTP结合的Ypt7p存在于两个被拴系膜中时，系系才会发生。然而，当啤酒花没有被磷酸化时，它的拴系活性对Ypt7p的核苷酸结合状态几乎没有显示出特异性。这些结果提出了一种啤酒花介导的系系模型，在该模型中，啤酒花通过与两个系留膜中的Ypt7p结合来系系膜。此外，由于液泡相关的啤酒花可能被Yck 3p磷酸化，我们的结果表明，Ypt7p在多囊体(MVB)/晚内体上的核苷酸交换必须在啤酒花能够介导空泡的拴系之前发生。
The HOPS/class C Vps complex, the effector for the yeast vacuolar Rab GTPase Ypt7p, tethers low-curvature membranes by binding to a Rab GTPase in each apposed membrane. This is the first time that the interactions with distinct membranes that give rise to Rab effector–dependent membrane tethering have been identified. Many Rab GTPase effectors are membrane-tethering factors, that is, they physically link two apposed membranes before intracellular membrane fusion. In this study, we investigate the distinct binding factors needed on apposed membranes for Rab effector–dependent tethering. We show that the homotypic fusion and protein-sorting/class C vacuole protein-sorting (HOPS/class C Vps) complex can tether low-curvature membranes, that is, liposomes with a diameter of ∼100 nm, only when the yeast vacuolar Rab GTPase Ypt7p is present in both tethered membranes. When HOPS is phosphorylated by the vacuolar casein kinase I, Yck3p, tethering only takes place when GTP-bound Ypt7p is present in both tethered membranes. When HOPS is not phosphorylated, however, its tethering activity shows little specificity for the nucleotide-binding state of Ypt7p. These results suggest a model for HOPS-mediated tethering in which HOPS tethers membranes by binding to Ypt7p in each of the two tethered membranes. Moreover, because vacuole-associated HOPS is presumably phosphorylated by Yck3p, our results suggest that nucleotide exchange of Ypt7p on multivesicular bodies (MVBs)/late endosomes must take place before HOPS can mediate tethering at vacuoles.