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.