Effect of Pseudomonas aeruginosa elastase and alkaline protease on serum complement and isolated components C1q and C3

Abstract The present study was undertaken to examine and compare the direct effect of two Pseudomonas enzymes, elastase and alkaline protease, on the serum hemolytic complement as a whole, and on the two recognition molecules of complement, C1q and C3 in particular. The results of our study show that incubation of serum with 0–50 μg/ml elastase or protease (60 min, 37°C) resulted in a dose-dependent depletion of hemolytic complement with the protease being 3–4 times more efficient than elastase. Incubation of highly purified C3 (20 hr, 37°C) with protease (2% w/w) resulted in the conversion of the 190-kDa molecule to a 120-kDa fragment. When analyzed by SDS-PAGE under reducing conditions, the 120-kDa piece yielded three distinct bands: an intact 75-kDa β-chain and two α-chain pieces of approximately 41- and 26-kDa. NH 2 -terminal end sequence analysis localized the 26-kDa fragment within the cysteine-rich 41-kDa, COOH-terminal piece. This in turn suggests that the 70-kDa fragment which is not accounted for on SDS-PAGE is derived from the NH 2 -terminal end of the α-chain molecule which is completely degraded into small fragments. While the degradation pattern obtained with elastase is similar to that of protease, the latter enzyme was found to be more efficient. Exposure of C1q (0–5 hr, 37°C) to protease or elastase on the other hand appears to reveal preferential sensitivity of the 28-kDa A-chain and 24-kDa C-chain, of the C1q molecule, with the protease being more potent than the elastase. Since both C1q and physiologic fragments of C3 (C3b, iC3b, and C3dg) are important opsonins of varying efficiencies, degradation of these molecules by Pseudomonas enzymes may, in part, facilitate the survival and proliferation of the organism in plasma. Furthermore, degradation of the key recognition molecules of complement, C1q and C3, would enhance the virulence of this organism by aborting complement-mediated bacterial killing. In addition the results imply that during Pseudomonas bacteremia, PaAP may be a much more destructive enzyme than PaE with regards to C3 and C1q but combined, the synergistic effect may overwhelm not only the proteins of the complement system, but other proteins of the humoral immune defense system as well.