Department of Surgery, Division of Ophthalmology, University of New Mexico, Albuquerque, NM 87131, USA.
Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, BC V5Z 3N9, Canada.
J Cell Sci. 2018 Dec 10;131(24):jcs222034. doi: 10.1242/jcs.222034.
The Arf4-rhodopsin complex (mediated by the VxPx motif in rhodopsin) initiates expansion of vertebrate rod photoreceptor cilia-derived light-sensing organelles through stepwise assembly of a conserved trafficking network. Here, we examine its role in the sorting of VAMP7 (also known as TI-VAMP) - an R-SNARE possessing a regulatory longin domain (LD) - into rhodopsin transport carriers (RTCs). During RTC formation and trafficking, VAMP7 colocalizes with the ciliary cargo rhodopsin and interacts with the Rab11-Rabin8-Rab8 trafficking module. Rab11 and Rab8 bind the VAMP7 LD, whereas Rabin8 (also known as RAB3IP) interacts with the SNARE domain. The Arf/Rab11 effector FIP3 (also known as RAB11FIP3) regulates VAMP7 access to Rab11. At the ciliary base, VAMP7 forms a complex with the cognate SNAREs syntaxin 3 and SNAP-25. When expressed in transgenic animals, a GFP-VAMP7ΔLD fusion protein and a Y45E phosphomimetic mutant colocalize with endogenous VAMP7. The GFP-VAMP7-R150E mutant displays considerable localization defects that imply an important role of the R-SNARE motif in intracellular trafficking, rather than cognate SNARE pairing. Our study defines the link between VAMP7 and the ciliary targeting nexus that is conserved across diverse cell types, and contributes to general understanding of how functional Arf and Rab networks assemble SNAREs in membrane trafficking.
Arf4-视蛋白复合物（由视蛋白中的 VxPx 基序介导）通过逐步组装保守的运输网络，启动脊椎动物棒状光感受器纤毛衍生的光感受细胞器的扩张。在这里，我们研究了它在 VAMP7（也称为 TI-VAMP）分选中的作用 - 一种具有调节性 longin 结构域（LD）的 R-SNARE - 进入视蛋白运输载体（RTC）。在 RTC 形成和运输过程中，VAMP7 与纤毛货物视蛋白共定位，并与 Rab11-Rabin8-Rab8 运输模块相互作用。Rab11 和 Rab8 结合 VAMP7 LD，而 Rabin8（也称为 RAB3IP）与 SNARE 结构域相互作用。Arf/Rab11 效应因子 FIP3（也称为 RAB11FIP3）调节 VAMP7 对 Rab11 的访问。在纤毛基部，VAMP7 与同源 SNAREs 突触素 3 和 SNAP-25 形成复合物。当在转基因动物中表达时，GFP-VAMP7ΔLD 融合蛋白和 Y45E 磷酸模拟突变体与内源性 VAMP7 共定位。GFP-VAMP7-R150E 突变体显示出相当大的定位缺陷，这意味着 R-SNARE 基序在细胞内运输中起着重要作用，而不是同源 SNARE 配对。我们的研究定义了 VAMP7 与纤毛靶向枢纽之间的联系，该联系在不同的细胞类型中是保守的，并有助于理解功能性 Arf 和 Rab 网络如何在膜运输中组装 SNARE。
