Crosslinking by ZapD drives the assembly of short FtsZ filaments into toroidal structures in solution

Abstract

In most bacteria, division depends on a cytoskeletal structure, the FtsZ ring, that functions as a scaffold to recruit additional proteins, with which it forms the machinery responsible for division, the divisome. The detailed architecture of the ring, in particular the mechanisms of assembly, stabilization, and disassembly, are still largely unknown. Here, we highlight the role of FtsZ-associated proteins (Zaps) that stabilize the FtsZ ring by crosslinking the filaments. Among Zap proteins, ZapD binds the C-terminal domain of FtsZ, which serves as a hub for its regulation. We demonstrate that ZapD crosslinks FtsZ filaments into ring-like structures formed by a discontinuous arrangement of short filaments. Using cryo-electron tomography combined with biochemical analysis, we reveal the three-dimensional organization of the ring-like structures and shed light on the mechanism of FtsZ filament crosslinking by ZapD. Together, our data provide a model of how FtsZ-associated proteins can stabilize FtsZ filaments into discontinuous ring-like structures reminiscent of that existing in the bacterial cell.