Protein D2 porin of the Pseudomonas aeruginosa outer membrane bears the protease activity

We report here our discovery that protein D2 of the outer membrane of Pseudomonas aeruginosa is a novel porin bearing protease activity, Homogeneously purified protein D2 hydrolyzed several synthetic peptides according to the Michaelis-Menten kinetics, A specific serine protease inhibitor, diisopropyl fluorophosphate (DFP), inactivated the protease activity and [H-3]DFP covalently labeled protein D2, We tested the effect of two monoclonal antibodies raised against protein D2 on the protease activity, One antibody lowered the protease activity to about 20%, while the other enhanced it to about 300% of that without antibody, In addition, the fractions derived from the outer membrane of the protein D2-deficient mutants showed negligible protease activity, whereas similarly fractionated outer membrane proteins of the protein D2-positive parent strain showed strong protease activity.