Retromer

Retromer is a complex of proteins that has been shown to be important in recycling transmembrane receptors from endosomes to the trans-Golgi network (TGN).

Retromer is a heteropentameric complex which in humans is composed of a less defined membrane-associated sorting nexin dimer (SNX1, SNX2, SNX5, SNX6), and a vacuolar protein sorting (Vps) trimer containing Vps26, Vps29, Vps35. Although the SNX dimer is required for the recruitment of retromer to the endosomal membrane, the cargo binding function of this complex is contributed by the core trimer through the binding of Vps35 subunit to various cargo molecules including M6PRwntless and sortilin. Early study on sorting of acid hydrolases such as carboxypeptidase Y (CPY) in S. cerevisiae mutants has led to the identification of retromer in mediating the retrograde trafficking of the pro-CPY receptor (Vps10) from the endosomes to the TGN.

The retromer complex is highly conserved: homologs have been found in C. elegans, mouse and human. The retromer complex consists of 5 proteins in yeast: Vps35p, Vps26p, Vps29p, Vps17p, Vps5p. The mammalian retromer consists of Vps26, Vps29, Vps35, SNX1 and SNX2, and possibly SNX5 and SNX6. It is proposed to act in two subcomplexes: (1) Cargo recognition complex that consist of Vps35, Vps29 and Vps26 (Vps trimer), and (2) SNX-BAR dimers which consist of SNX1 or SNX2 and SNX5 or SNX6 that facilitates endosomal membrane remodulation and curvature resulting in the formation of tubules/vesicles which transports cargo molecules to the trans-golgi network (TGN).

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