Abstract
The mechanisms of Z-ring assembly and regulation in bacteria are poorly understood, particularly in non-model organisms. Actinobacteria, a large bacterial phylum that includes the pathogen Mycobacterium tuberculosis, lack the canonical FtsZ-membrane anchors and Z-ring regulators described for E. coli. Here we investigate the physiological function of Corynebacterium glutamicum SepF, the only cell division-associated protein from Actinobacteria known to interact with the conserved C-terminal tail of FtsZ. We show an essential interdependence of FtsZ and SepF for formation of a functional Z-ring in C. glutamicum. The crystal structure of the SepF–FtsZ complex reveals a hydrophobic FtsZ-binding pocket, which defines the SepF homodimer as the functional unit, and suggests a reversible oligomerization interface. FtsZ filaments and lipid membranes have opposing effects on SepF polymerization, indicating that SepF has multiple roles at the cell division site, involving FtsZ bundling, Z-ring tethering and membrane reshaping activities that are needed for proper Z-ring assembly and function.
Highlights
The mechanisms of Z-ring assembly and regulation in bacteria are poorly understood, in non-model organisms
We found that incubation of SepF with small unilamellar vesicles (SUVs) led to SepF concentration-dependent polymerization in turbidity assays (Fig. 5a and Supplementary Fig. 16) and to the formation of large structures in dynamic light scattering (DLS) experiments (Supplementary Fig. 17a–c)
We demonstrated that SepF and FtsZ are interdependent to form a functional Z-ring and that SepF is essential in C. glutamicum
Summary
The mechanisms of Z-ring assembly and regulation in bacteria are poorly understood, in non-model organisms. In the best studied organisms, such as Escherichia coli and Bacillus subtilis, the action of several auxiliary proteins is necessary to positively or negatively regulate Z-ring formation (EzrA, ZapA-D3–7), to tether the structure to the membrane (FtsA, ZipA, SepF8–11), and to ensure proper subcellular (mid-cell) localization (SlmA, Noc, MinC/MinD12–14). Most of these proteins exert their functions by binding directly to the highly conserved FtsZ C-terminal domain (FtsZCTD)[15], which is separated from the core GTPase domain by an intrinsically disordered linker of variable length and sequence. We show that SepF has a complex dynamic role at the division site and that the ternary interaction between SepF, FtsZ, and the membrane, coupled to FtsZ polymerization dynamics, are all required for proper function and assembly
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