Filament-forming cytoskeletal GTPase. Forms a filamentous structure with SEPTIN12, SEPTIN6, SEPTIN2 and probably SEPTIN4 at the sperm annulus which is required for the structural integrity and motility of the sperm tail during postmeiotic differentiation (PubMed:25588830). Required for normal organization of the actin cytoskeleton. Plays a role in the biogenesis of polarized columnar-shaped epithelium by maintaining polyglutamylated microtubules, thus facilitating efficient vesicle transport, and by impeding MAP4 binding to tubulin. Required for the progression through mitosis. Forms a scaffold at the midplane of the mitotic splindle required to maintain CENPE localization at kinetochores and consequently chromosome congression. During anaphase, may be required for chromosome segregation and spindle elongation. Plays a role in ciliogenesis and collective cell movements. In cilia, required for the integrity of the diffusion barrier at the base of the primary cilium that prevents diffusion of transmembrane proteins between the cilia and plasma membranes: probably acts by regulating the assembly of the tectonic-like complex (also named B9 complex) by localizing TMEM231 protein. May play a role in the internalization of 2 intracellular microbial pathogens, Listeria monocytogenes and Shigella flexneri. Septins polymerize into heterooligomeric protein complexes that form filaments, and associate with cellular membranes, actin filaments and microtubules (PubMed:17637674, PubMed:25588830, Ref.36). GTPase activity is required for filament formation. Filaments are assembled from asymmetrical heterotrimers, composed of SEPTIN2, SEPTIN6 and SEPTIN7 that associate head-to-head to form a hexameric unit (PubMed:16093351, PubMed:16914550). Interaction between SEPTIN2 and SEPTIN7 seems indirect. Interacts with SEPTIN5 (By similarity). Interaction with SEPTIN4 not detected (By similarity). Interacts with SEPTIN9 (PubMed:19145258). Component of a septin core octomeric complex consisting of SEPTIN12, SEPTIN7, SEPTIN6 and SEPTIN2 or SEPTIN4 in the order 12-7-6-2-2-6-7-12 or 12-7-6-4-4-6-7-12 and located in the sperm annulus (PubMed:16093351, PubMed:16914550). Interacts with MAP4. Interacts with DZIP1L (PubMed:28530676). In metaphase cells, localized within the microtubule spindle. At the metaphase plate, in close apposition to the kinetochores of the congressed chromosomes. In cells undergoing cytokinesis, localized to the midbody, the ingressing cleavage furrow, and the central spindle. During bacterial infection, displays a collar shape structure next to actin at the pole of invading bacteria. In epithelial cells, colocalizes with polyglutamylated tubulin around the trans-Golgi network, as well as juxatnuclear and proximal Golgi apparatus. Localizes at the base of the cilia near the morphological distinction between the cilia and plasma membranes. Found in the sperm annulus (PubMed:25588830). Widely expressed. Up-regulated in liver cancer. Coordinated expression with SEPTIN6 and SEPTIN7. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. Septin GTPase family. Extended N-terminus.