A revised order of subunits in mammalian septin complexes

Author(s)

Mendonca, Deborah C. ^[1] ; Macedo, Joci N. ^{[1, 2]} ; Guimaraes, Samuel L. ^[1] ; Barroso da Silva, Fernando L. ^{[3, 4]} ; Cassago, Alexandre ^[5] ; Garratt, Richard C. ^[1] ; Portugal, Rodrigo V. ^[5] ; Araujo, Ana P. U. ^[1]

Affiliation

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

^[2] Fed Inst Educ Sci & Technol Rondonia, Vilhena - Brazil

^[3] Univ Sao Paulo, Fac Pharmaceut Sci, Ribeirao Preto, SP - Brazil

^[4] Univ Paris Diderot, UMR S 1134, Paris - France

^[5] CNPEM, Brazilian Nanotechnol Natl Lab, Campinas, SP - Brazil

• Document type: Journal article
• Source: CYTOSKELETON; v. 76, n. 9-10, p. 457-466, SEP 2019.
• Web of Science Citations: 0

Abstract

Septins are GTP binding proteins considered to be novel components of the cytoskeleton. They polymerize into filaments based on hexameric or octameric core particles in which two copies of either three or four different septins, respectively, assemble into a specific sequence. Viable combinations of the 13 human septins are believed to obey substitution rules in which the different septins involved must come from distinct subgroups. The hexameric assembly, for example, has been reported to be SEPT7-SEPT6-SEPT2-SEPT2-SEPT6-SEPT7. Here, we have replaced SEPT2 by SEPT5 according to the substitution rules and used transmission electron microscopy to demonstrate that the resulting recombinant complex assembles into hexameric particles which are inverted with respect that predicted previously. MBP-SEPT5 constructs and immunostaining show that SEPT5 occupies the terminal positions of the hexamer. We further show that this is also true for the assembly including SEPT2, in direct contradiction with that reported previously. Consequently, both complexes expose an NC interface, as reported for yeast, which we show to be more susceptible to high salt concentrations. The correct assembly for the canonical combination of septins 2-6-7 is therefore established to be SEPT2-SEPT6-SEPT7-SEPT7-SEPT6-SEPT2, implying the need for revision of the mechanisms involved in filament assembly. (AU)

• FAPESP's process: 15/16116-3 - Molecular mechanisms of electrostatic origin responsible for protein complexation
• Grantee: Fernando Luis Barroso da Silva
• Support Opportunities: Regular Research Grants
• 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
• 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