Oxidative dissociation of human alpha 2-macroglobulin tetramers into dysfunctional dimers.

作者：Vivek Yerrapu Reddy, P.E. Desorchers, Salvatore Vincent Pizzo, Steve L. Gonias, Julie A. Sahakian, Rodney L. Levine, Stephen J. Weiss · 发表于：Journal of Biological Chemistry · 年份：1994 · DOI：10.1016/s0021-9258(17)41830-8 · 被引用次数：111 · 研究领域：Protease and Inhibitor Mechanisms、Peptidase Inhibition and Analysis、Signaling Pathways in Disease

Human alpha 2-macroglobulin is a broad-spectrum, homotetrameric antiproteinase that can maximally bind up to two proteinase molecules in a ternary complex. Proteinases cleave the inhibitor within a peptide stretch termed the bait region and induce the emergence of internal thiol esters whose nucleophilic scission precede a major conformational change which entraps enzymes within molecular cages. In a previous study, leukocyte-generated hypohalous acids and N-haloamines were identified as the first examples of physiologically relevant inactivators of the antiproteolytic activity of alpha 2-macroglobulin (Reddy, V. Y., Pizzo, S. V., and Weiss, S. J. (1989) J. Biol. Chem. 264, 13801-13809), but the mechanisms whereby the oxidants damaged the inhibitor remained undefined. We now demonstrate that N-chloramines (RNCl) destroy the antiproteolytic activity of alpha 2-macroglobulin in an unusual biphasic process that results in the formation of inactive alpha 2-macroglobulin half-molecules. In the first phase, 8 eq of RNCl reacted with each alpha 2-macroglobulin subunit to generate a partially oxidized antiproteinase containing 8 methionyl sulfoxide residues/monomer. Structure-function analyses demonstrated that the oxidized inhibitor retained its homotetrameric structure as well as its ability to entrap proteinases. In marked contrast, the oxidation of an additional 6 methionyl residues and a single tryptophanyl residue fractured the alpha 2 M homotetramer across its non-covalent axi...