Functional conservation of a natural cysteine peptidase inhibitor in protozoan and bacterial pathogens.

Cysteine peptidase inhibitor genes (ICP) of the chagasin family have been identified in protozoan (Leishmania mexicana and Trypanosoma brucei) and bacterial (Pseudomonas aeruginosa) pathogens. The encoded proteins have low sequence identities with each other and no significant identity with cystatins or other known cysteine peptidase inhibitors. Recombinant forms of each ICP inhibit protozoan and mammalian clan CA, family C1 cysteine peptidases but do not inhibit the clan CD cysteine peptidase caspase 3, the serine peptidase trypsin or the aspartic peptidases pepsin and thrombin. The functional homology between ICPs implies a common evolutionary origin for these bacterial and protozoal proteins.