Mapping the extended substrate binding site of cathepsin G and human leukocyte elastase. Studies with peptide substrates related to the alpha 1-protease inhibitor reactive site.

Abstract

The kinetic constants for the hydrolysis of a series of I-nitroanilide substrates by human leukocyte (HL) elastase and cathepsin G, porcine pancreatic elastase, and bovine chymotrypsin at pH 7.50 are reported.HL elastase and cathepsin G are currently thought to be the agents responsible for destruction of the lung in the disease emphysema.MeO-Sue-Ala-Ala-Pro-VaI-NA is an excellent substrate for HL elastase and is not hydrolyzed by cathepsin G.The MeO-Sue-group increases the solubility of a substrate relative to the acetyl group.With HL elastase, this structural change increases the reactivity of the enzyme toward both I-nitroanilide substrates and chloromethyl ketone inhibitors.This indicates that HL elastase is interacting with at least 5 residues of a substrate (or inhibitor).Cathepsin G prefers Pb groups which are negatively charged such as Sue-, Suc(4F)-, Glt-, or Mal-.This enzyme, in common with many other serine proteases cannot accept a Pro residue at its Ss subsite.One of the better substrates for cathepsin G, Sue-Ala-Ala-Pro-Phe-NA, was not hydrolyzed by HL elastase.These tools should be useful in the study of the biological function of HL elastase and cathepsin G. Two tetrapeptide 4-nitroanilide substrates related to the reactive site of the plasma (~1' protease inhibitor (ai-antitrypsin) were studied.Both have a P1 Met residue and one, MeO-Suc-Ala-Ile-Pro-Met-NA, has the exact sequence of the Pa to Pt residues at the proteolysis site of al-PI (Johnson, D. A., and Travis, J. (1978) J. BioL Clrem.253, 7142-7144).Both MeO-Sue-Ala-Ala-Pro-Met-NA and MeO-Suc-Ala-Ile-Pro-Met-NA react with cathepsin G, HL elastase, and bovine chymotrypsin.The former is in fact the best 4nitroanilide substrate of cathepsin G yet reported.Oxidation of MeO-Sue-Ala-Ala-Pro-Met-NA yielded two diastereomeric sulfoxides.Neither are bound to or was hydrolyzed by HL elastase or cathepsin G.Both reacted poorly