The Huck Institutes of the Life Sciences

CsrA-FliW interaction governs flagellin homeostasis and a checkpoint on flagellar morphogenesis in Bacillus subtilis

Mukherjee, S., Yakhnin, H., Kysela, D., Sokoloski, J., Babitzke, P., and Kearns, D. B. (2011) MolMicrobiol 82, 447-461

We previously determined that CsrA represses flagellin (Hag) synthesis in B. subtilis by binding to hag mRNA and repressing translation. The Mukherjee et al. paper identifies a novel mechanism to control bacterial CsrA activity.

Rather than the widespread use of sRNA-mediated sequestration of CsrA protein, we found that Bacillus subtilisFliW acts as the first known protein antagonist of CsrA activity. FliW, CsrA and Hag participate in a protein partner switching mechanism to control Hag synthesis.

CsrA into FliW (A) Hag into FliW (B)
Kd = 20 nM Kd = 140 nM

Following completion of the flagellar hook, secretion of Hag releases FliW so that it can bind to CsrA, which relieves CsrA-mediated translational repression of hag for just-in-time Hag synthesis. Thus, Hag homeostatically restricts its own translation.

We used auto-ITC to measure the affinity and stoichiometry of the FliW-CsrA and FliW-Hag protein-protein interactions.

Mukherjee et al.