Septins: the fourth component of the cytoskeleton

Key Points Septins belong to a family of GTP-binding proteins that is highly conserved in eukaryotes and is recognized as a novel component of the cytoskeleton. They assemble to form hetero-oligomeric complexes, filaments, bundles and rings. How septins assemble for function, and how they interact and work in conjunction with actin, microtubules and phospholipids, is the focus of intense investigation. Septins have recently been reported to act as scaffolds for protein recruitment at the plasma membrane and in the cytosol, and as diffusion barriers for subcellular compartmentalization at the bases of cilia, at the annuli of spermatozoa and at the bases of dendritic spines in neurons. Studies of host–microorganism interactions have highlighted roles for septins in bacterial invasion and autophagy. Septin biology will help to decipher the molecular mechanisms underlying human diseases in which septins have been implicated, such as cancer, neurological disorders and infections. Septins are highly conserved, GTP-binding proteins that form hetero-oligomeric complexes and higher-order structures, such as filaments and rings. By acting as scaffolds or diffusion barriers, they have roles in numerous biological processes, including cell division and host–pathogen interactions. Septins belong to a family of proteins that is highly conserved in eukaryotes and is increasingly recognized as a novel component of the cytoskeleton. All septins are GTP-binding proteins that form hetero-oligomeric complexes and higher-order structures, including filaments and rings. Recent studies have provided structural information about the different levels of septin organization; however, the crucial structural determinants and factors responsible for septin assembly remain unclear. Investigations on the molecular functions of septins have highlighted their roles as scaffolds for protein recruitment and as diffusion barriers for subcellular compartmentalization in numerous biological processes, including cell division and host–microorganism interactions.