Studies on the Sorting Mechanism of the Yeast SNARE Vti1p and the Identification and Characterization of the Yeast BAR Domain Containing Protein Gvp36p

Membrane traffic in eukaryotic cells requires the interaction between SNAREs on transport vesicles and SNAREs on target membranes. Vti1p (Vps10 interacting 1) is a yeast SNARE, which is involved in a number of transport steps as part of four different SNARE complexes. It is found in SNARE complexes which function on the Golgi, endosomes, and the vacuole. The ability of Vti1p to mediate multiple fusion steps presumably requires distinct protein sorting factors (proteins) to ensure the fidelity of its trafficking. As Vti1p regulates multiple vesicle transport steps to many different organelles, identifying its trafficking partners is a complex task that remains to be completed. To address this I have initiated a study to identify the sorting signals and pathways of Vti1p. By co-purification experiment, I found that three clathrin-associated adaptor protein complexes (APs), AP-1, AP-2 and AP-3, interact with Vti1p and facilitate its transport between the Golgi, plasma membrane and endosomal / vacuolar compartments, respectively. I have also established that the interaction between Vti1p and the APs is dependent on a D/EXXXLL-like adaptin-dependent sorting motif (D46ELFDLL52). The mutant vti1LL-AA (L51A; L52A) was not co-purified with APs. Furthermore, I found that Gga2p (a presumptive coat protein), Ent3p (a lipid-binding domain containing protein) and Gvp36p (a BAR-domain containing protein) were also involved in sorting of Vti1p.;In my related study, a yeast novel protein Gvp36p was identified as a BAR domain containing protein. BAR domains have a capacity to bind to curved membranes and therefore may participate in maintaining organelle shape and/or in stabilizing membrane deformation as a prelude to transport vesicle formation. Structure prediction and biochemical data suggest that Gvp36p contains a BAR domain. The functional analysis shows that Gvp36p is involved in multiple pathways and functions on the post-Golgi compartments associating with Ent3p, Gga2p, and APs.