Filament-forming cytoskeletal GTPase (By similarity). May play a role in platelet secretion (PubMed:15116257). Seems to participate in the process of SNARE complex formation in synaptic vesicles (By similarity). Stabilizes BACE1 protein levels and promotes the sorting and accumulation of BACE1 to the recycling or endosomal compartments, modulating the beta-amyloidogenic processing of APP. 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 (PubMed:12098780). Interacts with SEPTIN5 (PubMed:12909369). Interacts with SEPTIN7 (By similarity). Interacts with SEPTIN4 (PubMed:15116257). 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 (By similarity). In platelets, found in areas surrounding alpha-granules (PubMed:15116257). Widely expressed, including in brain, heart and platelets; most abundant in aorta. Isoform 2 is expressed at low levels in specific brain areas, such as occipital pole, frontal lobe, temporal lobe and putamen. Isoform 1 and 3 are highly expressed in specific brain areas, such as occipital pole, frontal lobe, temporal lobe and putamen. Isoform 2 is highly expressed in prostate, testis and ovary. Isoform 1 and isoform 3 are expressed at low levels in prostate, testis and ovary. KIAA0202a differs from KIAA0202c at the level of the 3'-UTR. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family. Extended N-terminus. Truncated N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus.