CetZs are cytoskeletal proteins unique to the archaeal domain and are homologues of eukaryotic tubulin and bacterial FtsZ. CetZs are tubulin superfamily proteins which are abundant in almost all cell types and have a wide range of structural roles. Despite constituting a major group within the tubulin superfamily and being conserved across several groups of Archaea, CetZs are understudied compared to tubulin and FtsZ, and their basic biological functions are still being uncovered.
CetZs were first implicated in the control of cell shape and motility in Haloferax volcanii. We have discovered that two distinct paralogs, CetZ1 and CetZ2, coordinate their activities to alter cell shape during starvation, likely via a direct interaction that mediates their contrasting roles (Brown & Duggin, 2023; Brown & Duggin, 2024b). Further investigation found these CetZs have additional distinct roles in the assembly and positioning of cell surface structures, including chemotaxis sensor arrays and archaella, which are equivalent to the bacterial flagellum (Brown et al, 2024). Consistent with these findings, high-resolution fluorescence imaging has revealed that CetZs have complex dynamic localization patterns at the cell envelope, particularly at the cell poles, along the cell length and at mid-cell (de Silva et al, 2024). We also show that multiple Min protein positioning systems differentially control these specific localisations, which are important in cell motility (Brown & Duggin, 2024a). Thus, the dynamic and complex localisation patterns of CetZ1 and CetZ2 are consistent with their coordinated roles in multiple cellular functions.
Together these findings reveal distinct biological roles of CetZ paralogues, connect CetZ function with multiple molecular pathways, and demonstrate functional specialisation of cytoskeletal proteins in archaea. They also aid our understanding of the evolutionary history of tubulin superfamily proteins, which are likely to have evolved from a single FtsZ in bacteria to multiple tubulins in eukaryotes with complex coordinated activities.