Analyses of a novel function for SNAP-23 in phagosome maturation

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Phagosome maturation in phagocytes is thought to be accomplished by membrane fusion of phagosome with other organelles, but the molecular mechanism in this process remains unknown.In this study, we have found SNAP-23, a plasma membrane-localized SNARE, functions not only in phagocytosis but also in phagosome maturation processes such as production of reactive oxygen species and acidification within phagosomes and fusion of phagosome with lysosome. To trace a conformational change of SNAP-23 during fusion event, we established a single-molecule fluorescence resonance energy transfer system for SNAP-23. Using this system, we have found a forming SNARE complex with VAMP7 on phagosomal membrane and a novel complex including VAMP5 and syntaxin3 on plasma membrane. This suggests that SNAP-23 mediates the membrane fusion of phagosome with lysosome by forming a SNARE complex with VAMP7. Unfortunately, we have never found a positive function of VAMP5 in phagosome formation and maturation.