Neuronal-specific septin-3 (UniProt Q9UH03) is encoded by the SEPT3 (also known as SEP3) gene (Gene ID 55964) in human. Septins are GTPases capable of forming higher-order oligomers and filamentous polymers that contact with cell membrane and cytoskeleton. Septins are involved in various cellular processes, including cytokinesis, karyokinesis, exocytosis, and cell shape maintenance. Septins exist in complexes that are composed of ordered non-polar arrays of multiple different septins. Human genome contains 13 septin genes that are grouped into the SEPT2 subgroup (septins 1, 2, 4, and 5), the SEPT3 subgroup (septins 3, 9, and 12), the SEPT6 subgroup (septins 6, 8, 10, 11, and 14), and the SEPT7 subgroup (septin 7). All subgroups contain the well conserved GTP-binding domain and differ mainly in their C-terminal region, where coiled-coil sequences are found in SEPT2, SEPT6, and SEPT7, but not SEPT3, subgroups. Septin-3 is the only septin to be expressed almost exclusively in brain tissue, where it is enriched in nerve terminals, suggesting a role in synaptic vesicle function. Increased septin-3 expression is reported in several brain tumors and SEPT3 polymorphisms are linked to Alzheimer's disease. PKG-1 is shown to phosphorylate septin-3 in vitro, non-phosphorylated septin-3 localizes to the peripheral membrane, whereas the phosphorylated form is found in the cytosol. Murine and rat septin-3 is reported to form complexes with septin-5 and septin-7.
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