The Rab family of proteins includes small, monomeric GTPases essential for regulating intracellular vesicle trafficking. Members of the Rab3 subfamily, including Rab3A-3D, are involved in the exocytosis of neurotransmitters and hormones. Rab3A is primarily expressed in neurons, neuroendocrine cells, and in human pancreatic β cells. By acting as a molecular switch between active GTP-bound Rab3A and the inactive GDP-bound form, Rab3A inhibits synaptic vesicle and chromaffin granule secretion during late membrane release. Loss-of-function studies suggest Rab3A is involved in controlling synaptic vesicle targeting and docking at the active zone. Through binding to its direct effector Rabphillin, Rab3A also orchestrates the coupling between synaptic vesicle exocytosis and endocytosis.
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