This project is designed to further our understanding of membrane trafficking in the eukaryotic cell. Vesicular transport is a process by which protein and lipids move between cellular compartments; it is crucial for the generation and maintenance of these compartments. Vesicle fusion with specific compartments is mediated by interaction between integral membrane proteins on vesicular and target membranes, termed v-SNAREs and t-SNARES , respectively. Interaction of v- and t-SNARES could not account by itself for the high fidelity of intracellular trafficking. The tethering factors and small GTP-binding proteins of the Rab family are thought to ensure the specificity of vesicle targeting. It is extremely important to understand the interplay among SNAREs, Rabs and tethering factors in the regulation of vesicle targeting and fusion.
Studies in yeast and mammalian cells have led to the identification of several multisubunit peripheral membrane protein complexes that are involved in membrane trafficking, including the Sec6/8, the TRAPP, the Vps52/53/54, and the Sec34p complexes. The eukaryotic Sec34p complex, named COG (for conserved oligomeric Golgi complex) has eight subunits, is localized to the Golgi apparatus, and has been suggested to be involved in anterograde ER to Golgi, retrograde intra-Golgi, endosome to Golgi traffic, as well as in sorting of GPI-anchored proteins upon ER exit. Dr. Lupashin's laboratory has recently demonstrated that mutations in the COG complex subunits result in defects in basic Golgi functions, including glycosylation of secretory proteins, protein sorting, and retention of Golgi resident proteins . Furthermore, the COG complex interacts genetically and physically with the Rab protein Ypt1p, Golgi SNARE molecules, and with the Golgi vesicle coat complex COPI. Dr. Lupashin's main hypothesis is that the COG complex acts as a tether that connects cis-Golgi membranes and COPI-coated, retrogradely targeted intra-Golgi vesicles. There are three specific aims to this project: 1, a detailed molecular characterization of the COG complex composition; 2, to investigate molecular interactions of the COG complex with other components of vesicle trafficking machinery; and 3, to characterize the role of the COG complex in intra-Golgi vesicle trafficking.
Ultimately, the long-term goal of this study is to decipher some of the mechanisms that regulate specific targeting of transport vesicles in eukaryotic cells. One of the most significant challenges for the membrane traffic field in the coming years will be to gain an understanding of the role of tethering factors in membrane transport, and with Dr. Lupashin's background he should be able to make significant advances in understanding this process.
Dr. Lupashin teaches in several graduate courses, including a new interdisciplinary graduate cell biology course that he developed. In addition, he interacts with faculty and students at nearby undergraduate institutions such as the University of Arkansas Little Rock and the University of Arkansas Community College at Batesville. This grant will support a graduate student and a postdoctoral trainee.
