SYNTAXIN-13 MEDIATES CYCLING OF PLASMA-MEMBRANE PROTEINS VIA TUBULOVESICULAR RECYCLING ENDOSOMES

Endocytosis-mediated recycling of plasma membrane is a critical vesicl e trafficking step important in diverse biological processes. The memb rane trafficking decisions and sorting events take place in a series o f heterogeneous and highly dynamic organelles, the endosomes. Syntaxin 13, a recently discovered member of the syntaxin family, has been sug gested to play a role in mediating endosomal trafficking. To better un derstand the function of syntaxin 13 we examined its intracellular dis tribution in nonpolarized cells. By confocal immunofluorescence and el ectron microscopy, syntaxin 13 is primarily found in tubular early and recycling endosomes, where it colocalizes with transferrin receptor. Additional labeling is also present in endosomal vacuoles, where it is often found in clathrin-coated membrane areas. Furthermore, anti-synt axin 13 antibody inhibits transferrin receptor recycling in permeabili zed PC12 cells. Immunoprecipitation of syntaxin 13 revealed that, in T riton X-100 extracts, syntaxin 13 is present in a complex(es) comprise d of beta SNAP, VAMP 2/3, and SNAP-25. This complex(es) binds exogenou sly added alpha SNAP and NSF and dissociates in the presence of ATP, b ut not ATP gamma S. These results support a role for syntaxin 13 in me mbrane fusion events during the recycling of plasma membrane proteins.