Truncated type IV pilin PilA108 activates the intramembrane protease AlgW to cleave MucA and PilA108 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 PilA 108 with a C-terminal motif of phenylalanine–threonine–phenylalanine (FTF), induced mucoidy in strain PAO579. In this study, we purified PilA 108 protein and synthesized a peptide ‘SGAGDITFTF’ corresponding to C-terminus of PilA 108 and found they both caused the degradation of MucA by AlgW. Interestingly, AlgW could also cleave PilA 108 between alanine 62 and glycine 63 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.