ELASTASE AND THE LASA PROTEASE OF PSEUDOMONAS-AERUGINOSA ARE SECRETEDWITH THEIR PROPEPTIDES

Pseudomonas aeruginosa elastase and the LasA protease are synthesized as preproenzymes with long amino-terminal propeptides, The elastase pr opeptide is cleaved autocatalytically in the periplasm to form a trans ient, inactive elastase-propeptide complex. In contrast, the processin g of proLasA does not involve autoproteolysis. In this study, we analy zed short-term P, aeruginosa cultures under conditions that minimize p roteolysis and found that an elastase-propeptide complex is secreted, and then the propeptide is degraded extracellularly, apparently by ela stase itself. LasA protease, on the other hand, was found to be secret ed in its unprocessed 42-kDa proenzyme form. The processing of proLasA occurred extracellularly, and it involved the transient appearance of a 28-kDa intermediate and the respective 14-kDa LasA propeptide fragm ent. The processing of proLasA in P, aeruginosa strain FRD740, which d oes not express elastase, also proceeded via the 28-kDa intermediate, but the rate of processing was greatly reduced. This low rate of proLa sA processing was further reduced when the activity of a secreted lysi ne-specific protease was blocked. Purified secreted proteases of P, ae ruginosa (i.e, elastase, the lysine-specific protease, and alkaline pr oteinase) converted proLasA to the active enzyme. Processing by elasta se and the lysine-specific enzyme, but not by alkaline proteinase, pro ceeded via the 28-kDa intermediate, and both were far more effective t han alkaline proteinase in con verting proLasA to the mature enzyme. W e conclude that LasA protease and elastase are secreted with their pro peptides, which are then degraded by secreted proteases of P. aerugino sa, In addition to their other functions, the propeptides may play a r ole in targeting their respective enzymes across the outer membrane.