Structures of the nucleoid occlusion protein SlmA bound to DNA and the C-terminal domain of the cytoskeletal protein FtsZ

Abstract:

Cell division in most prokaryotes is mediated by FtsZ, which polymerizes to create the cytokinetic Z ring. Multiple FtsZ-binding proteins regulate FtsZ polymerization to ensure the proper spatiotemporal formation of the Z ring at the division site. The DNA-binding protein SlmA binds to FtsZ and prevents Z-ring formation through the nucleoid in a process called “nucleoid occlusion” (NO). As do most FtsZ-accessory proteins, SlmA interacts with the conserved C-terminal domain (CTD) that is connected to the FtsZ core by a long, flexible linker. However, SlmA is distinct from other regulatory factors in that it must be DNA-bound to interact with the FtsZ CTD. Few structures of FtsZ regulator–CTD complexes are available, but all reveal the CTD bound as a helix. To deduce the molecular basis for the unique SlmA–DNA–FtsZ CTD regulatory interaction and provide insight into FtsZ–regulator protein complex formation, we determined structures of Escherichia coli, Vibrio cholera, and Klebsiella pneumonia SlmA–DNA–FtsZ CTD ternary complexes. Strikingly, the FtsZ CTD does not interact with SlmA as a helix but binds as an extended conformation in a narrow, surface-exposed pocket formed only in the DNA-bound state of SlmA and located at the junction between the DNA-binding and C-terminal dimer domains. Binding studies are consistent with the structure and underscore key interactions in complex formation. Combined, these data reveal the molecular basis for the SlmA–DNA–FtsZ interaction with implications for SlmA’s NO function and underscore the ability of the FtsZ CTD to adopt a wide range of conformations, explaining its ability to bind diverse regulatory proteins.

Importancia:

The bacterial protein FtsZ polymerizes into protofilaments to create the cytokinetic ring responsible for directing cell division. Cellular levels of FtsZ are above the concentration required for Z-ring formation. Hence, FtsZ-binding proteins have evolved that control its spatiotemporal formation. The SlmA protein is one such factor that, when bound to specific chromosomal DNA, inhibits FtsZ polymerization to prevent Z rings from forming through the bacterial chromosome. This inhibition depends on complex formation between SlmA-DNA and the FtsZ C-terminal domain (CTD). Here we describe SlmA–DNA–FtsZ CTD structures. These structures and complementary biochemistry unveil the molecular basis for the unique requirement that SlmA be DNA-bound to interact with FtsZ, a mechanism that appears to be conserved among SlmA-containing bacteria.

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