Zn2+ enhances the molecular chaperone function and stability of alpha-crystallin.
Alpha-crystallin, the major eye lens protein, is a molecular chaperone that plays a crucial role in the suppression of protein aggregation and thus in the long-term maintenance of lens transparency. Zinc is a micronutrient of the eye, but its molecular interaction with alpha-crystallin has not been studied in detail. In this paper, we present results of in vitro experiments that show bivalent zinc specifically interacts with alpha-crystallin with a dissociation constant in the submillimolar range (Kd approximately 0.2-0.4 mM). We compared the effect of Zn2+ with those of Ca2+, Cu2+, Mg2+, Cd2+, Pb2+, Ni2+, Fe2+, and Co2+ at 1 mM on the structure and chaperoning ability of alpha-crystallin. An insulin aggregation assay showed that among the bivalent metal ions, only 1 mM Zn2+ improved the chaperone function of alpha-crystallin by 30% compared to that in the absence of bivalent metal ions. Addition of 1 mM Zn2+ increased the yield of alpha-crystallin-assisted refolding of urea-treated LDH to its native state from 33 to 38%, but other bivalent ions had little effect. The surface hydrophobicity of alpha-crystallin was increased by 50% due to the binding of Zn2+. In the presence of 1 mM Zn2+, the stability of alpha-crystallin was enhanced by 36 kJ/mol, and it became more resistant to tryptic cleavage. The implications of enhanced stability and molecular chaperone activity of alpha-crystallin in the presence of Zn2+ are discussed in terms of its role in the long-term maintenance of lens transparency and cataract formation.
Biswas
Ashis
A
Protein Chemistry Laboratory, Department of Chemistry, Bose Institute, 93/1 APC Road, Kolkata 700 009, India.
Das
Kali P
KP
D000817:Anilino Naphthalenesulfonates / Q000378:metabolism; D002413:Cations, Divalent / Q000494:pharmacology; D002942:Circular Dichroism; D003300:Copper / Q000378:metabolism / Q000494:pharmacology; D004228:Dithionitrobenzoic Acid / Q000378:metabolism; D004492:Edetic Acid; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism*; D009282:Naphthalenesulfonates / Q000378:metabolism; D017510:Protein Folding; D013050:Spectrometry, Fluorescence; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013816:Thermodynamics; D013997:Time Factors; D014357:Trypsin / Q000378:metabolism; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology*; D038202:alpha-Crystallin A Chain / Q000378:metabolism*; D038203:alpha-Crystallin B Chain / Q000378:metabolism*
D000817:Anilino Naphthalenesulfonates; D002413:Cations, Divalent; D018832:Molecular Chaperones; D009282:Naphthalenesulfonates; D013438:Sulfhydryl Compounds; D038202:alpha-Crystallin A Chain; D038203:alpha-Crystallin B Chain; C035763:5,5'-bis(8-(phenylamino)-1-naphthalenesulfonate); C009497:2-(4-toluidino)-6-naphthalenesulfonic acid; D003300:Copper; D004228:Dithionitrobenzoic Acid; D004492:Edetic Acid; D007770:L-Lactate Dehydrogenase; D014357:Trypsin; D015032:Zinc