Dynamic self-association of archaeal tubulin-like protein CetZ1 drives Haloferax volcanii morphogenesis

Tubulin superfamily (TSF) proteins include the well-known eukaryotic tubulin and bacterial FtsZ families, and lesser-known archaeal CetZ family. In eukaryotes and bacteria, GTP-dependent polymerization and self-association of tubulin and FtsZ protofilaments are integral to the formation of cytoskeletal structures with essential roles in cell division, growth, and morphology. Archaeal CetZs are implicated in the control of cell shape and motility through unknown mechanisms. Here, we reveal a sequence of subcellular localization patterns of CetZ1, the prototypical member of the CetZ family, during stages of Haloferax volcanii rod cell development, in which it plays an essential role. Like tubulin and FtsZ, we found that CetZ1 formed GTP-dependent polymers in vitro, which appear to associate laterally as irregular polymer bundles. Mutations targeting regions predicted to mediate self-association and dynamic turnover of CetZ1, including the longitudinal (GTPase T7 and T4 loops) and lateral assembly interfaces, perturbed or altered rod shape development and subcellular assembly and dynamics, and caused corresponding effects on polymerization in vitro. Remarkably, a conspicuous amphipathic protrusion in the large microtubule (M-) loop, a characteristic of the CetZ1 subfamily, also strongly influenced function and assembly. Our findings reveal the importance of dynamic CetZ1 self-association in cellular morphogenesis involving multiple regions of the TSF fold, including tubulin- and FtsZ-like structural characteristics and CetZ1-specific features. Furthermore, they support a mechanism involving CetZ1 dynamic guidance of cell envelope-associated structures that reshape the cell during morphogenesis.