TRAPP complexes in membrane traffic: convergence through a common Rab

Transport protein particle (TRAPP; also known as trafficking protein particle) complexes activate the GTPase Ypt1 or RAB1 to regulate membrane traffic in yeast and mammals, respectively. Two different TRAPP complexes tether coated vesicles during endoplasmic reticulum–Golgi and intra-Golgi traffic, respectively, and a third complex functions in autophagy. The TRAPP complexes thereby connect GTPase activation to unique membrane-tethering events. Transport protein particle (TRAPP; also known as trafficking protein particle), a multimeric guanine nucleotide-exchange factor for the yeast GTPase Ypt1 and its mammalian homologue, RAB1, regulates multiple membrane trafficking pathways. TRAPP complexes exist in three forms, each of which activates Ypt1 or RAB1 through a common core of subunits and regulates complex localization through distinct subunits. Whereas TRAPPI and TRAPPII tether coated vesicles during endoplasmic reticulum to Golgi and intra-Golgi traffic, respectively, TRAPPIII has recently been shown to be reqiured for autophagy. These advances illustrate how the TRAPP complexes link Ypt1 and RAB1 activation to distinct membrane-tethering events.