An interaction network between the SNARE VAMP7 and Rab GTPases within a ciliary membrane-targeting complex

Abstract

The Arf4-rhodopsin complex (mediated by the VxPx motif in rhodopsin) initiates expansion of vertebrate rod photoreceptor ciliaderived 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.

Pan-cancer investigation reveals mechanistic insights of planar cell polarity gene Fuz in carcinogenesis

“…The presence of Longin domain is broadly shared by vesicle trafficking proteins [ 48 , 49 ]. These Longin domain-containing proteins transport specific cargos and target their membrane localization in support of cilia outgrowth, which is impaired when protein dysfunctions occur [ 11 , 50 ]. Interestingly, the R404Q mutation was initially identified from human patients with neural tube defects, a severe neurological deficit due to the failure of neural tube closure during embryonic development, and Seo et al [ 47 ] showed that Fuz R404Q mutant prevents cilia elongation and directional cell movements.…”

The photoreceptor cilium and its diseases

“…and Syntaxin3 [23,26,27], explaining the observed massive accumulation of unfused vesicles in cc2d2a-/-zebrafish PRs.…”

Compartmentalization of Photoreceptor Sensory Cilia

“…Rabin8 is recruited to the developing vesicle and leads to the formation of the Rab11-Rabin8-Rab8 module. The Rab11-Rabin8-Rab8 module recruits the SNARE component VAMP7 into the budding secretory vesicles, called rhodopsin transport carriers (RTCs) (Deretic et al, 2004 ; Wang and Deretic, 2014 ), making them competent for fusion with the plasma membrane near the base of the cilium containing the partner SNARE components syntaxin 3 and SNAP25 (Kandachar et al, 2018 ).…”