PURIFICATION AND CHARACTERIZATION OF PROCYTOTOXIN OF PSEUDOMONAS-AERUGINOSA - DIMER TO MONOMER CONVERSION OF PROTOXIN BY PROTEOLYTIC ACTIVATION

Cytotoxin of Pseudomonas aeruginosa is a cytolytic toxin that forms a pore on the target membrane by oligomerizing into a pentamer. This tox in is produced as an inactive precursor (proCTX) and is converted to a n active form by proteolytic cleavage at the C terminus. We purified p roCTX to apparent homogeneity and characterized it in a comparison wit h the active toxin. ProCTX bound to the erythrocyte membrane but did n ot form an oligomer on the membrane, hence the lack of hemolytic activ ity in proCTX, Circular dichroic experiments showed that active and pr oCTX have similar beta-sheet dominant structures. Intrinsic fluorescen ce analysis indicated that a molecule-buried tryptophan residue(s) of proCTX was exposed to the surface of the molecule as a result of conve rsion to the active form, In analytical gel filtration, chemical cross -linking, and analytical ultracentrifugation experiments, dimer to mon omer conversion occurred with proteolytic activation.