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The SNARE protein SNAP‐29 interacts with the GTPase Rab3A: Implications for membrane trafficking in myelinating glia

During myelin formation, vast amounts of specialized membrane proteins and lipids are trafficked toward the growing sheath in cell surface‐directed transport vesicles. Soluble N‐ethylmaleimide‐sensitive factor (NSF) attachment proteins (SNAPs) are important components of molecular complexes required for membrane fusion. We have analyzed the expression profile and molecular interactions of SNAP‐29 in the nervous system. In addition to its known enrichment in neuronal synapses, SNAP‐29 is abundant in oligodendrocytes during myelination and in noncompact myelin of the peripheral nervous system. By yeast two‐hybrid screen and coimmunoprecipitation, we found that the GTPases Rab3A, Rab24, and septin 4 bind to the N‐terminal domain of SNAP‐29. The interaction with Rab24 or septin 4 was GTP independent. In contrast, interaction between SNAP‐29 and Rab3A was GTP dependent, and colocalization was extensive both in synapses and in myelinating glia. In HEK293 cells, cytoplasmic SNAP‐29 pools were redistributed upon coexpression with Rab3A, and surface‐directed trafficking of myelin proteolipid protein was enhanced by overexpression of SNAP‐29 and Rab3A. Interestingly, the abundance of SNAP‐29 in sciatic nerves was increased during remyelination and in a rat model of Charcot‐Marie‐Tooth disease, two pathological situations with increased myelin membrane biogenesis. We suggest that Rab3A may regulate SNAP‐29‐mediated membrane fusion during myelination. © 2009 Wiley‐Liss, Inc.