ABSTRACT
Hypochlorous acid (HOCl), the active ingredient in household bleach, is an effective antimicrobial produced by the mammalian host defense to kill invading microorganisms. Despite the widespread use of HOCl, surprisingly little is known about its mode of action. In this study, we demonstrate that low molar ratios of HOCl to protein cause oxidative protein unfolding in vitro and target thermolabile proteins for irreversible aggregation in vivo. As a defense mechanism, bacteria use the redox-regulated chaperone Hsp33, which responds to bleach treatment with the reversible oxidative unfolding of its C-terminal redox switch domain. HOCl-mediated unfolding turns inactive Hsp33 into a highly active chaperone holdase, which protects essential Escherichia coli proteins against HOCl-induced aggregation and increases bacterial HOCl resistance. Our results substantially improve our molecular understanding about HOCl's functional mechanism. They suggest that the antimicrobial effects of bleach are largely based on HOCl's ability to cause aggregation of essential bacterial proteins.
Subject(s)
Hypochlorous Acid/pharmacology , Oxidation-Reduction , Disulfides , Escherichia coli/metabolism , Escherichia coli Proteins/metabolism , Heat-Shock Proteins/metabolism , Models, Biological , Molecular Chaperones/metabolism , Molecular Conformation , Oxygen/metabolism , Protein Denaturation , Protein Structure, Tertiary , Reactive Oxygen Species , Substrate Specificity , Sulfhydryl Compounds/chemistry , TemperatureABSTRACT
The conserved heat shock protein Hsp33 functions as a potent molecular chaperone with a highly sophisticated regulation. On transcriptional level, the Hsp33 gene is under heat shock control; on posttranslational level, the Hsp33 protein is under oxidative stress control. This dual regulation appears to reflect the close but rather neglected connection between heat shock and oxidative stress. The redox sensor in Hsp33 is a cysteine center that coordinates zinc under reducing, inactivating conditions and that forms two intramolecular disulfide bonds under oxidizing, activating conditions. Hsp33's redox-regulated chaperone activity appears to specifically protect proteins and cells from the otherwise deleterious effects of reactive oxygen species. That redox regulation of chaperone activity is not restricted to Hsp33 became evident when the chaperone activity of protein disulfide isomerase was recently also shown to cycle between a low- and high-affinity substrate binding state, depending on the redox state of its cysteines.
