Interaction of mouse macrophage elastase with native and oxidized human α1-proteinase inhibitor

Abstract

Native and oxidized α1-proteinase inhibitor (α1-PI) were compared as substrates for the metalloproteinase macrophage elastase. At substrate concentrations at which native α1-PI was readily degraded by macrophage elastase, oxidized α1-PI was hardly degraded at all. Incubation of macrophage elastase with oxidized α1-PI before the addition of native α1-PI showed that oxidized α1-PI was not an inhibitor of macrophage elastase. Competition experiments with up to twofold excess oxidized α1-PI did not interfere with the degradation of native α1-PI by macrophage elastase. Sequence analysis of amino acids in degraded native α1-PI showed that macrophage elastase attacked a single peptide bond between Pro-357 and Met-358, the latter representing the P1 reactive-site residue of α1-PI. In oxidized α1-PI, Met-358 was converted to methionine sulfoxide and macrophage elastase hydrolyzed the bond between Phe-352 and Leu-353. These data suggest that methionine may be the primary cleavage site for macrophage elastase and not leucine, as previously thought.