Filament-forming cytoskeletal GTPase (By similarity). May play a role in cytokinesis (Potential). 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). In cultured hippocampal neurons, predominantly localized to presynaptic terminals. Brain-specific, with highest expression in the hippocampal CA3 region (at protein level). First expressed in the embryonic brain from E18. Levels increase during brain development until P7 and remain constant until P35. Further increase in adult brain (at protein level). Phosphorylated by PKG on serine residues. Phosphorylated by PKG on Ser-91. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family.