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 ? 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