Filament-forming cytoskeletal GTPase (By similarity). May play a role in platelet secretion (By similarity). Seems to participate in the process of SNARE complex formation in synaptic vesicles (By similarity). Septins polymerize into heterooligomeric protein complexes that form filaments, and can associate with cellular membranes, actin filaments and microtubules. GTPase activity is required for filament formation (By similarity). Interacts with CDK14, SEPTIN4, SEPTIN5 and SEPTIN7 (By similarity). Interacts with VAMP2; the interaction inhibits interaction of VAMP2 with SYP (By similarity). Interacts with STX1A (By similarity). Expressed in axons of immature neurons, localizes to synapses in mature neurons. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family.