An atomic model for the human septin hexamer by cryo-EM

Author(s)

Mendonca, Deborah C. ^[1] ; Guimaraes, Samuel L. ^[1] ; Pereira, Humberto D'Muniz ^[1] ; Pinto, Andressa A. ^[1] ; de Farias, Marcelo A. ^[2] ; de Godoy, Andre S. ^[1] ; Araujo, Ana P. U. ^[1] ; van Heel, Marin ^[2] ; Portugal, V, Rodrigo ; Garratt, Richard C. ^[1]

Affiliation

^[1] Univ Sao Paulo, Sao Carlos Inst Phys, Sao Carlos, SP - Brazil

^[2] V, CNPEM, Brazilian Nanotechnol Natl Lab, Campinas, SP - Brazil

• Document type: Journal article
• Source: Journal of Molecular Biology; v. 433, n. 15 JUL 23 2021.
• Web of Science Citations: 0

Abstract

In 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 similar to 3.6 angstrom and a local resolution of between similar to 3.0 angstrom and similar to 5.0 angstrom. 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. (C) 2021 Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 17/15340-2 - EMU: acquisition of a transmission electron microscope for single particle cryo electron microscopy - establishing a cryo electron microscopy open facility at CNPEM
• Grantee: Rodrigo Villares Portugal
• Support Opportunities: Multi-user Equipment Program
• FAPESP's process: 18/20209-5 - Structural studies on the assembly of septin complexes by transmission electron microscopy and single particle analysis
• Grantee: Deborah Cezar Mendonça
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 18/20816-9 - Single-particle Cryo-EM analysis of septin heterocomplexes
• Grantee: Samuel Leite Guimarães
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• FAPESP's process: 14/15546-1 - Septins: comparative studies and the correlation between structure and function
• Grantee: Richard Charles Garratt
• Support Opportunities: Research Projects - Thematic Grants