<i>In vivo</i> and <i>in vitro</i> analyses of the role of the Prc protease in inducing mucoidy in <i>Pseudomonas aeruginosa</i>

After colonizing the lungs of individuals with cystic fibrosis, <i>Pseudomonas aeruginosa</i> undergoes mutagenic conversion to a mucoid form, worsening the prognosis. Most mucoid isolates have a truncated negative regulatory protein MucA, which leads to constitutive production of the extracellular polysaccharide alginate. The protease Prc has been implicated, but not shown, to degrade the most common MucA variant, MucA22, to trigger alginate production. This work provides the first demonstration that the molecular mechanism of Prc involvement is direct degradation of the MucA22 periplasmic domain and perhaps other truncated MucA variants as well. MucA truncation and degradation by Prc might be the predominant mechanism of mucoid conversion in cystic fibrosis infections, suggesting that Prc activity could be a useful therapeutic target.