Maturation of Pseudomonas aeruginosa elastase - Formation of the disulfidebonds

Elastase of Pseudomonas aeruginosa is synthesized as a preproenzyme. After propeptide-mediated folding in the periplasm, the proenzyme is autoproteoly tically processed, prior to translocation of both the mature enzyme and the propeptide across the outer membrane. The formation of the two disulfide b onds present in the mature enzyme was examined by studying the expression o f the wild-type enzyme and of alanine for cysteine mutant derivatives in th e authentic host and in dsb mutants of Escherichia coli. It appeared that t he two disulfide bonds are formed successively. First, DsbA catalyzes the f ormation of the disulfide bond between Cys-270 and Cys-297 within the proen zyme, This step is essential for the subsequent autoproteolytic processing to occur, The second disulfide bond between Cys-30 and Cys-57 is formed mor e slowly and appears to be formed after processing of the proenzyme, and it s formation is catalyzed by DsbA as well. This second disulfide bond appear ed to be required for the full proteolytic activity of the enzyme and contr ibutes to its stability.