Glycosaminoglycans regulate the inhibition of human leukocyte elastase by oxidized secretory leukoprotease inhibitor. Ying, Qi-Long, Michael Kemme, Derek Saunders, Sanford R. Simon. Departments of Pathology and Biochemistry and the Institute for Cell and Developmental Biology, State University of New York at Stony Brook, Stony Brook, New York 11794, USA, Institut f[umlaut]ur Biochemie, Technische Hochschule Darmstadt, Petersenstra[beta]e 22, D-64287 Darmstadt, and Department of Biotechnological Development, Gr[umlaut]unenthal GMBH, D-52220 Stolberg, Germany
APStracts 3:0218L, 1996.
Secretory leukoprotease inhibitor (SLPI) is one of the major physiological inhibitors protecting respiratory epithelium from attack by excess human leukocyte elastase (HLE), a serine protease released by neutrophils upon activation in response to inflammatory stimuli. Reaction with N-chlorotaurine, a major long-lived oxidant generated by activated neutrophils, oxidized all four methionine residues, but no other amino acids, in SLPI, resulting in substantial diminution of its elastase inhibitory activity. Oxidation of the P1' residue, Met73, accounted for most of the diminution in activity since a site-directed mutant of SLPI with leucine at the P1' position retained much higher residual activity after reaction with N -chlorotaurine. The diminished activity of oxidized SLPI could be almost completely restored when an iduronate-containing glycosaminoglycan, such as heparin, heparan sulfate or dermatan sulfate, was added to the reaction medium. Addition of a sulfated, glucuronate-containing glycosaminoglycan, chondroitin 4- or 6 -sulfate, to the medium resulted in smaller but significant restoration of the lost activity; whereas the effects of hyaluronic acid and keratan sulfate were negligible. Kinetic analysis revealed that glycosaminoglycans greatly accelerated the association of oxidized SLPI and HLE, while iduronate-containing glycosaminoglycans also stabilized the enzyme-inhibitor complex formed. Based on these findings, we suggest that oxidized SLPI is a functionally active form of the inhibitor but expression of its elastase inhibitory activity is regulated by sulfated, uronate-containing glycosaminoglycans. Since its methionine residues have already been oxidized, this form of SLPI is resistant to the oxidant species which selectively attack methionine residues in proteins. These findings indicate that SLPI may play a previously unexpected role in elastase inhibitory function in the lungs when significant inflammation is present. 

Received 22 August 1996; accepted in final form 25 October 1996.
APS Manuscript Number L273-6.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996