This family consists of several Rab5-interacting proteins (RIP5 or Rab5ip) including ER membrane protein complex subunit 6 (EMC6) and RCAF1. The ras-related GTPase rab5 is rate-limiting for homotypic early endosome fusion. Rab5ip represents a novel rab5 interacting protein that may function on endocytic vesicles as a receptor for rab5-GDP and participate in the activation of rab5 [1]. EMC6 interacts with Rab5A and BECN1/Beclin 1 and regulates autophagosome formation [2]. EMC6 is part of the EMC complex, required for efficient folding of proteins in the ER [3] and for post-translational membrane insertion of tail-anchored (TA) proteins [4,5].

1: A novel membrane-anchored Rab5 interacting protein required for homotypic endosome fusion. Hoffenberg S, Liu X, Nikolova L, Hall HS, Dai W, Baughn RE, Dickey BF, Barbieri MA, Aballay A, Stahl PD, Knoll BJ; J Biol Chem 2000;275:24661-24669. PMID:10818110

2: A novel ER-localized transmembrane protein, EMC6, interacts with RAB5A and regulates cell autophagy. Li Y, Zhao Y, Hu J, Xiao J, Qu L, Wang Z, Ma D, Chen Y; Autophagy. 2013;9:150-163. PMID:23182941

3: Biosynthesis of ionotropic acetylcholine receptors requires the evolutionarily conserved ER membrane complex. Richard M, Boulin T, Robert VJ, Richmond JE, Bessereau JL; Proc Natl Acad Sci U S A. 2013;110:E1055-E1063. PMID:23431131

4: The architecture of EMC reveals a path for membrane protein insertion. O'Donnell JP, Phillips BP, Yagita Y, Juszkiewicz S, Wagner A, Malinverni D, Keenan RJ, Miller EA, Hegde RS; Elife. 2020; [Epub ahead of print] PMID:32459176

5: Structural basis for membrane insertion by the human ER membrane protein complex. Pleiner T, Tomaleri GP, Januszyk K, Inglis AJ, Hazu M, Voorhees RM; Science. 2020;369:433-436. PMID:32439656