Abstract
Small heat shock proteins (sHsps) are widely distributed among various types of organisms and function in preventing the irreversible aggregation of thermal denaturing proteins. Here, we report that Hsp17.6 from Methanolobus psychrophilus exhibited protection of proteins from oxidation inactivation. The overexpression of Hsp17.6 in Escherichia coli markedly increased the stationary phase cell density and survivability in HClO and H2O2. Treatments with 0.2 mM HClO or 10 mM H2O2 reduced malate dehydrogenase (MDH) activity to 57% and 77%, whereas the addition of Hsp17.6 recovered the activity to 70–90% and 86–100%, respectively. A similar effect for superoxide dismutase oxidation was determined for Hsp17.6. Non-reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis assays determined that the Hsp17.6 addition decreased H2O2-caused disulfide-linking protein contents and HClO-induced degradation of MDH; meanwhile, Hsp17.6 protein appeared to be oxidized with increased molecular weights. Mass spectrometry identified oxygen atoms introduced into the larger Hsp17.6 molecules, mainly at the aspartate and methionine residues. Substitution of some aspartate residues reduced Hsp17.6 in alleviating H2O2- and HClO-caused MDH inactivation and in enhancing the E. coli survivability in H2O2 and HClO, suggesting that the archaeal Hsp17.6 oxidation protection might depend on an “oxidant sink” effect, i.e., to consume the oxidants in environments via aspartate oxidation.
Highlights
Small heat shock proteins are well known in mitigation of protein aggregation at are distributed among some archaea and bacteria, and the predicted oxidant-susceptive high temperatures
This work reports that the archaeal sHsp Hsp17.6 and the paralog aspartate residues are conserved in the orthologs (Figure S6); the reported oxiHsp18.9 from M. psychrophilus, a psychrophilic methanogenic archaeon, alleviated the dation protective role of the archaeal sHsps in this work could be widely applicable
Protein oxidative inactivation and oxidative stress of E. coli imposed by H2 O2 and HClO, Higher dissolved oxygen contents could occur in cold water systems [27]; exhibiting an oxidation protection function
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The E. coli sHsps, IbpA/B were reported to be involved in resistance to copper-induced oxidative stress [14], and the cyanobacterial small heat-shock protein HspA was found to play roles in enhancing the bacterial tolerance to oxidative stress and stabilization of the thylakoid membrane proteins [15]. This indicates that sHsps from different organisms could have diverse functions. Hsp17.6 from the psychrophilic archaeon M. psychrophilius R15 plays a role in the mitigation of protein oxidative inactivation and improvement of E. coli survivability in H2 O2 and HClO, likely via oxidation of its aspartate residues to consume environmental oxidants
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