title: Hypochlorite-induced structural modifications enhance the chaperone activity of human α2-macroglobulin.
abstract: Hypochlorite, an oxidant generated in vivo by the innate immune system, kills invading pathogens largely by inducing the misfolding of microbial proteins. Concomitantly, the nonspecific activity of hypochlorite also damages host proteins, and the accumulation of damaged (misfolded) proteins is implicated in the pathology of a variety of debilitating human disorders (e.g., Alzheimer's disease, atherosclerosis, and arthritis). It is well-known that cells respond to oxidative stress by up-regulating proteostasis machinery, but the direct activation of mammalian chaperones by hypochlorite has not, to our knowledge, been previously reported. In this study, we show that hypochlorite-induced modifications of human α2-macroglobulin (α2M) markedly increase its chaperone activity by generating species, particularly dimers formed by dissociation of the native tetramer, which have enhanced surface hydrophobicity. Moreover, dimeric α2M is generated in whole-blood plasma in the presence of physiologically relevant amounts of hypochlorite. The chaperone activity of hypochlorite-modified α2M involves the formation of stable soluble complexes with misfolded client proteins, including heat-denatured enzymes, oxidized fibrinogen, oxidized LDL, and native or oxidized amyloid β-peptide (Aβ1-42). Here, we show that hypochlorite-modified α2M delivers its misfolded cargo to lipoprotein receptors on macrophages and reduces Aβ1-42 neurotoxicity. Our results support the conclusion that α2M is a specialized chaperone that prevents the extracellular accumulation of misfolded and potentially pathogenic proteins, particularly during innate immune system activity.
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; andIllawarra Health and Medical Research Institute and School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
authors.forename: Amy R
authors.initials: AR
authors.lastname: Wyatt
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; and.
authors.forename: Janet R
authors.initials: JR
authors.lastname: Kumita
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; and.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Mifsud
authors.affiliation: Illawarra Health and Medical Research Institute and School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
authors.forename: Cherrie A
authors.initials: CA
authors.lastname: Gooden
authors.affiliation: Illawarra Health and Medical Research Institute and School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia mrw@uow.edu.au cmd44@cam.ac.uk.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Wilson
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; and mrw@uow.edu.au cmd44@cam.ac.uk.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Dobson
mesh_terms: D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D006997:Hypochlorous Acid / Q000737:chemistry*; D007113:Immunity, Innate; D007249:Inflammation; D051379:Mice; D018832:Molecular Chaperones / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D013499:Surface Properties; D013816:Thermodynamics; D000511:alpha-Macroglobulins / Q000737:chemistry*
chemical_list: D018832:Molecular Chaperones; D016877:Oxidants; D000511:alpha-Macroglobulins; D006997:Hypochlorous Acid; D010100:Oxygen
keywords: clearance; inflammation; molecular chaperone; protein folding