Structural insights into the functional divergence of WhiB-like proteins in Mycobacterium tuberculosis

WhiB7 represents a distinct subclass of transcription factors in the WhiB-Like (Wbl) family, a unique group of iron-sulfur (4Fe-4S] cluster-containing proteins exclusive to the phylum of Actinobacteria. In Mycobacterium tuberculosis (Mtb), WhiB7 interacts with domain 4 of the primary sigma factor (sigma(A)(4)) in the RNA polymerase holoenzyme and activates genes involved in multiple drug resistance and redox homeostasis. Here, we report crystal structures of the WhiB7:sigma(A)(4) complex alone and bound to its target promoter DNA at 1.55-angstrom and 2.6-angstrom resolution, respectively. These structures show how WhiB7 regulates gene expression by interacting with both sigma(A)(4) and the AT-rich sequence upstream of the -35 promoter DNA via its C-terminal DNA-binding motif, the AT-hook. By combining comparative structural analysis of the two high-resolution sigma(A)(4)-bound Wbl structures with molecular and biochemical approaches, we identify the structural basis of the functional divergence between the two distinct subclasses of Wbl proteins in Mtb.

Automated summary

WhiB7 is a distinct subclass of transcription factors in the WhiB-Like (Wbl) family, interacting with the primary sigma factor (sigma(A)(4)) in RNA polymerase holoenzyme to regulate gene expression through its DNA-binding motif, the AT-hook. This study reveals the structural basis of functional divergence between the two subclasses of Wbl proteins in Mycobacterium tuberculosis through high-resolution structural analysis and molecular approaches.