Correct partner makes the difference: Septin G-interface plays a critical role in amyloid formation.

Septins are members of a group of GTP-binding proteins highly conserved in eukaryotes, being linked to diverse cell processes, such as cytokinesis and membrane association. On the other hand, the malfunction of septins is linked to several pathological processes including neurodegeneration and oncogenesis. Septins interact with each other forming heterocomplexes that polymerize in filaments. Two types of interface between septins alternate along the filament: the G-interface (involving the GTP binding sites), and the NC-interface. This work focuses on the physiological G-interface of SEPT2, used in the SEPT6G-SEPT2G heterodimer assembly, to verify the impact of this interaction on the thermostability and amyloid formation. We found that the SEPT6G-SEPT2G moves to an irreversible state with the ability to bind thioflavin-T at high temperatures, suggesting its amyloid-like nature. Noteworthy, this takes place at a higher temperature than the one observed to the single septins, showing greater thermal/structural stability. Taken together, our results show that in the absence of the partners, the septin becomes unstable and susceptible to amyloid aggregation/formation even in physiological temperatures, and the G-interface appears to have a critical role in this process.