CetZ1-dependent assembly and positioning of the motility machinery inhaloarchaea

Abstract

AbstractThe tubulin-like CetZ proteins are archaeal cytoskeletal proteins that contribute to cell shape and swimming motility in the halophilic archaeonHaloferax volcanii.Currently it is unknown whether CetZs contribute to motility solely through their control of cell shape or in other ways too. Here, we used cryo-electron andfluorescence microscopy to observeH. volcaniicell surface filaments and the localisation of the motility machinery, respectively, in strains withcetZ1orcetZ2deletion, overexpression, and polymerisation-defective mutant backgrounds. Our results show that CetZ1 has an important role at the poles of mature motile rod cells for the assembly of key motility proteins, including ArlD1, a constituent of the archaellum base, and the chemotaxis sensory array adapter CheW1 and signal transducer CheY. Importantly, overproduction of CetZ1 and CetZ1-mTurquoise2 inhibited motility and reduced the frequency of localisation of the motility machinery markers but did not aeect rod-shape in swimming cells. Our data suggest that CetZ1 acts as a polar cytoskeletal structure that orchestrates the assembly and positioning of both major components of the motility machinery. The multifunctionality and dynamic redeployment of CetZ1 during motile cell development is reminiscent of eukaryotic cytoskeletal proteins and the roles of tubulin at the base of the eukaryoticflagellum.Significance statementThis study demonstrates that archaeal CetZ tubulin-like cytoskeletal proteins control swimming motility through promoting the assembly of motility structures at cell poles, in addition to their established roles in rod morphology development. To achieve this, the conserved CetZ1 protein assembles as a cap or patch-like structures at the cell poles of mature motile rod cells of the model archaeal organism,H. volcanii. CetZ1 migration to the cell poles for assembly of motility structures has a primitive resemblance to the roles of tubulin in basal bodies essential to the development of eukaryoticflagella. Our findings represent the discovery of both multifunctionality and dynamic redeployment in an archaeal cytoskeletal protein, combined behaviours thought to be a characteristic of the eukaryotic cytoskeleton.