Filament-forming cytoskeletal GTPase (By similarity). May play a role in cytokinesis (Potential). May play a role in platelet secretion (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. Interacts with SEPTIN2 and SEPTIN5. In platelets, associated with a complex containing STX4. Interacts with PRKN; this interaction leads to SEPTIN5 ubiquitination and degradation (By similarity). Interacts with DYRK1A (By similarity). Interacts with STX1A; in the cerebellar cortex (By similarity). Phosphorylated by DYRK1A. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family.