DNA strongly impairs the inhibition of cathepsin G by α1- antichymotrypsin and α1-proteinase inhibitor

Abstract

This paper explores the possibility that neutrophil-derived DNA interferes with the inhibition of neutrophil cathepsin G (cat G) and proteinase 3 by the lung antiproteinases α1-proteinase inhibitor (α1PI), α1-antichymotrypsin (ACT), and mucus proteinase inhibitor (MPI). A 30-base pair DNA fragment ((30bp)DNA), used as a model of DNA, tightly binds cat G (K(d), 8.5 nM) but does not react with proteinase 3, α1PI, ACT, and MPI at physiological ionic strength. The polynucleotide is a partial noncompetitive inhibitor of cat G whose K(i) is close to K(d). ACT and α1PI are slow binding inhibitors of the cat G-(30bp)- DNA complex whose second-order rate constants of inhibition are 2300 M-1 s-1 and 21 M-1 s-1, respectively, which represents a 195-fold and a 3190-fold rate deceleration. DNA thus renders cat G virtually resistant to inhibition by these irreversible serpins. On the other hand, (30bp)DNA has little or no effect on the reversible inhibition of cat G by MPI or chymostatin or on the irreversible inhibition of cat G by carbobenzoxy-Gly-Leu-Phe- chloromethylketone. The polynucleotide neither inhibits proteinase 3 nor affects its rate of inhibition by α1PI. These findings suggest that cat G may cause lung tissue destruction despite the presence of antiproteinases.