An inter-subunit disulfide bond of artemin acts as a redox switch for its chaperone-like activity

摘要

Encysted embryos of Artemia are among the most stress-resistant eukaryotes partly due to the massive amount of a cysteine-rich protein termed artemin. High number of cysteine residues in artemin and their intramolecular spatial positions motivated us to investigate the role of the cysteine residues in the chaperone-like activity of artemin. According to the result of Ellman's assay, there are nine free thiols (seven buried and two exposed) and one disulfide bond per monomer of artemin. Subsequent theoretical analysis of the predicted 3D structure of artemin confirmed the data obtained by the spectroscopic study. Native and reduced/modified forms of artemin were also compared with respect to their efficiency in chaperoning activity, tertiary structure, and stability. Since the alkylation and reduction of artemin diminished its chaperone activity, it appears that its chaperoning potential depends on the formation of intermolecular disulfide bond and the presence of cysteine residues. Comparative fluorescence studies on the structure and stability of the native and reduced protein revealed some differences between them. Due to the redox-dependent functional switching of artemin from the less to more active form, it can be finally suggested as a redox-dependent chaperone.