Roles of the HOPS complex and Sec1/Munc18 proteins in membrane fusion.

摘要

A fundamental feature of the eukaryotic cell is its diversity of membrane bound compartments. Despite a constant flux of proteins and lipids through these compartments, organelle identity and function is maintained by regulating membrane fusion. Membrane fusion is driven by the coordinated action of a several families of proteins: Rabs, tethers, SMs, and SNAREs. Each compartment has its own paralogs of these proteins, and compartment identity is maintained by the specificity of this membrane fusion machinery. Individual SNARE proteins form a complex to catalyze membrane fusion, while Rabs, tethers, and SM proteins regulate SNARE activity. The universal factors Sec18 and Sec17, an ATPase and its adaptor, prime the SNARE proteins after each round of membrane fusion by disassembling the SNARE complex. The mechanisms by which these processes occur, however, are not fully understood. I have studied the conserved membrane fusion machinery of the lysosomal-vacuole using the S. cerevisiae model system, and then expanded my observations to the fusion machinery involved in ER to Golgi transport. Using biochemical and cell biological assays, I have examined the architecture of the vacuole-lysosomal tethering complex, and identified interactions sites within it for the other components of the fusion machinery. I have specifically focused on the role of SM proteins in membrane fusion. Using biochemical assays with purified components, I have characterized the SNARE binding properties of two SM proteins and identified a mechanistic function for SM proteins in kinetically shielding SNARE complexes from disassembly by ATPase Sec18.