Recombinant DNA-derived forms of human alpha 1-proteinase inhibitor. Studies on the alanine 358 and cysteine 358 substituted mutants.

The specificity and reactivity of human alpha 1-proteinase inhibitor has been investigated by in vitro mutagenesis of the reactive site P1 methionine 358 residue to alanine 358 and cysteine 358. A comparison of the second-order association rates of both uncharged mutants with 9 serine proteinases indicated that each reacted similarly to either the normal plasma inhibitor or to a mutant containing valine in this position (Travis, J., Owen, M., George, P., Carrell, R., Rosenberg, S., Hallewell, R. A., and Barr, P. J. (1985) J. Biol. Chem. 260, 4384-4389) when tested against either neutrophil or pancreatic elastase. However, oxidation, carboxymethylation, or aminoethylation of the cysteine mutant to yield a charged P1 residue resulted in a significant decrease in association rates with both elastolytic enzymes, and aminoethylation created an excellent trypsin and plasmin inhibitor. These results indicate that the specificity of alpha 1-proteinase inhibitor is determined in a general manner by the class of amino acid residue in the P1 position. Substitution within the same category, such as from valine to alanine or cysteine among the aliphatic hydrophobic residues, has little effect on association rates with the elastolytic enzymes tested. However, alteration from an uncharged to a charged residue may cause considerable changes in both inhibitor specificity and reactivity as noted here with the cysteine derivatives and also previously with a natural variant in which methionine 358 to arginine 358 conversion resulted in the production of a potent thrombin inhibitor (Owen, M. C., Brennan, S. O., Lewis, J. H., and Carrell, R. W. (1983) N. Engl. J. Med. 309, 694-698).