Septin 5 (SEPT5) belongs to the septin family. Septin 5, also known as CDCrel-1, is predominantly expressed in the nervous system, co-localises with synaptic vesicles and is involved in exocytosis []. In humans, its role in exocytotic secretion that is modulated by Cdk5 phosphorylation [, ]. SEPT5 interacts with SEPT8 and SEPT11. The complex formed by SEPT5 and SEPT11 is involved in the exocytosis mechanism in human umbilical vein endothelial cells (HUVECs) [].Septins were first discovered in budding yeast as a major component of bud neck filaments during cell septation [, ]. Later, its homologues were identified in nearly all eukaryotes, including humans. They are all GTP-binding proteins that are involved in diverse cellular functions, including cell cycle progression, vesicle trafficking, cytokinesis, cell migration, membrane dynamics, and chromosome segregation [, ]. Similar to cytoskeleton components such as actins and tubulins, they can assemble into filaments and bundles. However, unlike actin filaments and microtubules, septin filaments are not polar, similarly to intermediate filaments []. The number of septin genes per organism is variable: S. cerevisiae has seven and humans have 13 (SEPT1-12 and SEPT14; SEPT13 is a pseudogene now called SEPT7P2) []. All septins can form heteromeric complexes, which associate to form higher-order structures, including filaments, rings and cage-like formations [, ].
