Comparison of the Vibrio cholerae hemagglutinin/protease and the Pseudomonas aeruginosa elastase

The soluble hemagglutinin/protease (HA/protease) produced by Vibrio cholerae and the elastase of Pseudomonas aeruginosa are both zinc/calcium-dependent proteases. In the present study the two enzymes are compared immunologically and functionally. The N-terminal amino acid sequences of the proteins had 65% identity within the first 20 amino acids. Polyclonal antisera against each purified protein recognized the enzyme of the other species in enzyme-linked immunosorbent assay, checkerboard immunoblot, and Western blot analyses and inhibited the protease activity of both enzymes in milk and elastin agars. Like the HA/protease, the elastase hemagglutinated "responder" but not "nonresponder" chicken erythrocytes, degraded ovomucin, lactoferrin, and fibronectin, and nicked the A subunit of the cholera toxin-related heat-labile enterotoxin from Escherichia coli. Whereas none of the three proteases tested (elastase, HA/protease, or pronase E) had any obvious effect in ileal loop tests in rabbits at doses up to 50 micrograms, all three produced some detectable skin reactions at a dose of 0.1 micrograms and necrosis at a higher dose (i.e., 5 micrograms). We conclude that the V. cholerae HA/protease and the P. aeruginosa elastase are structurally, functionally, and immunologically related.