Institute for Protein Research (IPR), Osaka University
Molecular Machinery of Intracellular Membrane Fusion
"Understanding Intracellular Membrane Fusion by in vitro Reconstitution with Purified Membrane Proteins and Lipids"
Intracellular membrane fusion is a fundamental and conserved biological reaction of eukaryotic cells, which is vital for vesicle trafficking between cellular compartments, organelle morphology, hormone secretion, and neurotransmission. Fusion is regulated by specific proteins and lipids including Q-SNARE proteins, R-SNAREs, SNARE chaperones (incl. alpha-SNAP/Sec17p, NSF/Sec18p, Sec1/Munc18 family proteins, and synaptotagmin), Rab GTPases, diacylglycerol, sterols, and phopsphoinositides. However, it still remains unclear how these key components act together to mediate physiological highly-regulated "membrane fusion".
We study this vital membrane fusion machinery in eukaryotic cells with homotypic organelle fusion of yeast vacuoles/lysosomes and have recently developed the reconstituted proteoliposomal fusion with purified proteins/lipids all of which are essential components of this organelle membrane fusion (Mima et al (2008) EMBO J; Mima & Wickner (2009) PNAS; Mima & Wickner (2009) JBC; Hickey et al (2009) JBC; Stroupe et al (2009) PNAS). Our current aims are to further dissect the ternary synergy between two vacuolar SNARE chaperone systems (Sec17p/Sec18p/ATP and the HOPS complex) and phosphoinositides (PI(3)P and PI(4,5)P2), which is required for physiological/rapid/efficient membrane fusion through catalyzing the assembly and remodeling of fusion-competent SNARE complexes.