Stress-Dependent Conformational Changes of Artemin: Effects of Heat and Oxidant
Artemin is an abundant thermostable protein in Artemia embryos and considered as a highly efficient molecular chaperone against extreme environmental stress conditions. The dynamic conformational properties of artemin appear to play a critical role in its biological activities. In this study, we have investigated the conformational transitions and functional changes of artemin under heat and oxidative stress to find some evidence of the relationship between the structure and function of artemin. The tertiary and quaternary structures of artemin have been evaluated by fluorescence measurements, protein cross-linking analysis, and dynamic light scattering. Based on the structural analysis, artemin showed irreversible substantial conformational lability in response to heat and oxidant which mainly mediated through the hydrophobic interactions and dimerization of the chaperone. In addition, the chaperone-like activity of the heated and oxidized artemin was examined using lysozyme refolding assay and the experiments showed that although both factors, i.e. heat and oxidant, at specific levels improved artemin potency, simultaneous incubation with both stressors significantly triggered the activation of artemin. Moreover, the heat-induced dimerization of artemin was found to be the most critical factor for its activation. It was suggested that oxidation presumably acts through stabilizing the dimer structures of artemin through formation of disulfide bridges between the subunits and strengthens its chaperoning efficacy. Accordingly, it was proposed that artemin probably exists in a monomer-oligomer equilibrium in Artemia cysts and environmental stresses and intracellular portion of protein substrates may shift the equilibrium towards the active dimer forms of the chaperone. STATEMENT OF SIGNIFICANCEThere are a number of reports in which the chaperone-like activity of artemin, as a stress protein, has been confirmed in vivo and in vitro. Nonetheless, the details of structural changes of the protein have not been fully discovered yet. In the present work, we focused on conformational properties of artemin from A. urmiana upon exposing to heat and oxidation, by using various structural and functional analysis in order to predict the mechanisms of artemins activation. Notably, this is the first document on reporting the structural transitions of the chaperone in stress conditions.