Truncated type IV pilin PilA(108) activates the intramembrane protease AlgW to cleave MucA and PilA(108) itself in vitro.

For alginate production in Pseudomonas aeruginosa, the intramembrane protease AlgW must be activated to cleave the periplasmic domain of anti-sigma factor MucA for release of the sequestered ECF sigma factor AlgU. Previously, we reported that three tandem point mutations in the pilA gene, resulting in a truncated type IV pilin termed PilA108 with a C-terminal motif of phenylalanine–threonine–phenylalanine (FTF), induced mucoidy in strain PAO579. In this study, we purified PilA108 protein and synthesized a peptide ‘SGAGDITFTF’ corresponding to C-terminus of PilA108 and found they both caused the degradation of MucA by AlgW. Interestingly, AlgW could also cleave PilA108 between alanine62 and glycine63 residues. Overexpression of the recombinant FTF motif-bearing MucE protein, originally a small periplasmic polypeptide with the C-terminal motif WVF, could induce mucoid conversion in the PAO1 strain. In all, our results provided a model of activation of AlgW by another protein ending with proper motifs. Our data suggest that in addition to MucA cleavage, AlgW may cleave other substrates.