Exo70 as a Link Between Vesicle Targeting and Vesicle Fusion

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

How are secretory vesicles targeted to and fused with the plasma membrane? The answer to this question is fundamental to the understanding of how cells form specialized plasma membrane domains during growth and differentiation. In eukaryotic cells, secretory vesicles bud from the trans Golgi network (TGN) and are transported along cytoskeletal tracks to the vicinity of their site of fusion with the plasma membrane. The links between vesicle transport, targeting and fusion are just now beginning to be understood. This research will examine the role of Exo70p in these processes. Exo70p is the 70 kilodalton protein component of the yeast exocyst complex that is required for vesicle docking and fusion at sites of polarized growth. This complex contains at least 8 protein components, but little is known about their biochemical function. To gain a greater understanding of the mechanism of secretory vesicle targeting and fusion, the investigators will examine: 1)How Exo70 regulates the specificity of secretory vesicle targeting. 2)How Exo70 links vesicle targeting to the fusion machinery. The research combines the strengths of yeast genetics with biochemical and cell biological approaches. Genetic screens will be used to identify proteins that are required for secretory vesicle transport and for the specificity of vesicle targeting in an exo70-38 mutant. This project will explore the innovative idea that secretory vesicle transport and recognition may be directly coupled to vesicle fusion by Exo70p. Towards this end the project will determine whether an exocyst component protein can regulate the specificity of secretory vesicle docking. The expectations are that the project will provide new insights into how Exo70p links vesicle transport to vesicle docking, recognition and fusion at the plasma membrane. This will be accomplished by investigating the role of Exo70p in t-SNARE clustering at the site of fusion and how different classes of secretory vesicles can be discriminated during vesicle targeting/docking to the plasma membrane. In polarized epithelium, the exocyst complex is required for basolateral vesicle targeting and the exocyst is localized to the sites of polarized growth (growth cones) in developing neurons. Therefore, it is expected that insights gained from yeast studies such as these will be applicable to the understanding of the regulation of exocytosis in human cells.