The retromer subunit Vps26 has an arrestin fold and binds Vps35 through its C-terminal domain

Abstract

The mammalian retromer complex consists of SNX1, SNX2, Vps26, Vps29, and Vps35, and retrieves lysosomal enzyme receptors from endosomes to the trans-Golgi network. The structure of human Vps26A at 2.1Å resolution reveals two curvedβ -sandwich domains connected by a polar core and a flexible linker. Vps26 has an unexpected structural relationship to arrestins. The Vps35-binding site on Vps26 maps to a mobile loop spanning residues 235-246, near the tip of the C-terminal domain. The loop is phylogenetically conserved and provides a mechanism for Vps26 integration into the complex that leaves the rest of the structure free for engagements with membranes and for conformational changes. Hydrophobic residues and a Gly in this loop are required for integration into the retromer complex and endosomal localization of human Vps26, and for the function of yeast Vps26 in carboxypeptidase Y sorting.The biosynthetic sorting of acid hydrolase precursors from the trans-Golgi network (TGN) to the endosomal-lysosomal system is central to the biogenesis of lysosomes in metazoans. In mammals, this sorting is directed by binding of mannose 6-phosphate groups on the hydrolases to two transmembrane receptors known as the cation-dependent and cation-independent mannose 6-phosphate receptors (CD-MPR and CI-MPR, respectively) 1 . At the TGN, the hydrolase-receptor complexes are packaged into carrier vesicles by several coat and adaptor proteins, including clathrin, AP-1 (adaptor protein 1) and GGA (Golgi-localized, gamma earcontaining, ADP ribosylation factor-binding) proteins 1,2 . These carrier vesicles bud from the TGN and fuse with endosomes. Within the endosome, the acid pH in the lumen triggers the release of the hydrolases from their receptors. The hydrolases are carried with the fluid phase to lysosomes, while the receptors return to the TGN to be reutilized in further rounds of sorting. Several proteins and complexes, including AP-1 3,4 , TIP47 (tail-interacting protein of 47 kDa) 5 and PACS-1 (phosphofurin acidic cluster sorting protein) 6 have been implicated in the transport of MPRs from endosomes to the TGN.A similar process has been described in yeast cells for the sorting of acid hydrolases to the vacuole, which is the fungal equivalent of the mammalian lysosome. Carboxypeptidase Y (CPY) is sorted by the Vps10 transmembrane receptor. Genetic screens in yeast have identified more than 60 Vps (vacuolar protein sorting) gene products 7 , which are involved in the transport of CPY to the vacuole. Five yeast Vps proteins, Vps5, Vps17, Vps26, Vps29 and Vps35, form a complex named "retromer" that is required for Vps10 sorting from endosomes to the late-5 To whom correspondence should be addressed: James H. Hurley, (301) 402-4703, fax (301) A homologous retromer complex consisting of five subunits termed SNX1, SNX2, Vps26, Vps29 and Vps35 has been described in humans 8 . Depletion of some of these subunits in vivo by RNA interference (RNAi) impairs retrieval of the CI-MPR and results in its missorting to lysosomes, where...

Retromer Binds the FANSHY Sorting Motif in SorLA to Regulate Amyloid Precursor Protein Sorting and Processing

“…This is the first demonstration of a role for VPS26 in cargo binding and is consistent with the structural studies of VPS26 that revealed an arrestin-like conformation for the VPS26 protein and predicted a possible cargo-binding activity by analogy with the arrestin family of proteins (Shi et al, 2006;Collins et al, 2008). Although studies in both yeast and mammalian cells have indicated that VPS35 is responsible for the cargo-binding activity of retromer (Nothwehr et al, 2000;Arighi et al, 2004), our data suggest that this is not the case with respect to sorLA binding.…”

The retromer complex – endosomal protein recycling and beyond

“…Intriguingly the motif in the SorL1/ SorLA cytoplasmic tail is similar to a motif (FYVFSN) present in the yeast Vps10p tail that contributes to the endosome-to-Golgi retrieval of Vps10p (Cereghino et al, 1995), although there is also evidence that additional sequences in Vps10p contribute to interactions with Vps35p (Nothwehr et al, 2000). The recognition of cargo proteins by Vps26 might be expected as its structure was found to be similar to that of b-arrestin -an endocytic adaptor protein that sorts GPCRs into clathrin-coated pits (Shi et al, 2006;Collins et al, 2008). Interestingly, in mammals, Vps26 is present as two paralogues, encoded by the highly related genes Vps26a and Vps26b (Kerr et al, 2005).…”

Mechanisms Governing the Endosomal Membrane Recruitment of the Core Retromer in Arabidopsis

“…Arrows indicate punctate compartments, and asterisks point to abnormally enlarged/ vacuolated compartments labeled with VPS35a-GFP. Scale bars, 10 m. Core Retromer Can interact with an Arabidopsis Rab7 Homolog on Endosomal Membranes-Studies relying on the structural analysis of the mammalian VPS subcomplex suggested that the core retromer cannot bind directly to lipids (39,40). Indeed, the sequential action of two Rab GTPases, Rab5 and Rab7, regulates retromer recruitment to membranes in mammalian cells.…”