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Human Septin Hexameric Complex SEPT2G/SEPT6/SEPT7 by Single Particle Cryo-EM
Structural highlights
FunctionSEPT2_HUMAN Filament-forming cytoskeletal GTPase. 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.[1] [2] [3] [4] Publication Abstract from PubMedIn order to form functional filaments, human septins must assemble into hetero-oligomeric rod-like particles which polymerize end-to-end. The rules governing the assembly of these particles and the subsequent filaments are incompletely understood. Although crystallographic approaches have been successful in studying the separate components of the system, there has been difficulty in obtaining high resolution structures of the full particle. Here we report a first cryo-EM structure for a hexameric rod composed of human septins 2, 6 and 7 with a global resolution of ~3.6 A and a local resolution of between ~3.0 A and ~5.0 A. By fitting the previously determined high-resolution crystal structures of the component subunits into the cryo-EM map, we are able to provide an essentially complete model for the particle. This exposes SEPT2 NC-interfaces at the termini of the hexamer and leaves internal cavities between the SEPT6-SEPT7 pairs. The floor of the cavity is formed by the two alpha(0) helices including their polybasic regions. These are locked into place between the two subunits by interactions made with the alpha(5) and alpha(6) helices of the neighbouring monomer together with its polyacidic region. The cavity may serve to provide space allowing the subunits to move with respect to one another. The elongated particle shows a tendency to bend at its centre where two copies of SEPT7 form a homodimeric G-interface. Such bending is almost certainly related to the ability of septin filaments to recognize and even induce membrane curvature. An atomic model for the human septin hexamer by cryo-EM.,Mendonca DC, Guimaraes SL, Pereira HD, Pinto AA, de Farias MA, de Godoy AS, Araujo APU, van Heel M, Portugal RV, Garratt RC J Mol Biol. 2021 Jul 23;433(15):167096. doi: 10.1016/j.jmb.2021.167096. Epub 2021 , Jun 9. PMID:34116125[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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