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  • Title: Enhancement of chaperone function of alpha-crystallin by methylglyoxal modification.
    Author: Nagaraj RH, Oya-Ito T, Padayatti PS, Kumar R, Mehta S, West K, Levison B, Sun J, Crabb JW, Padival AK.
    Journal: Biochemistry; 2003 Sep 16; 42(36):10746-55. PubMed ID: 12962499.
    Abstract:
    The molecular chaperone function of alpha-crystallin in the lens prevents the aggregation and insolubilization of lens proteins that occur during the process of aging. We found that chemical modification of alpha-crystallin by a physiological alpha-dicarbonyl compound, methylglyoxal (MG), enhances its chaperone function. Protein-modifying sugars and ascorbate have no such effect and actually reduce chaperone function. Chaperone assay after immunoprecipitation or with immunoaffinity-purified argpyrimidine-alpha-crystallin indicates that 50-60% of the increased chaperone function is due to argpyrimidine-modified protein. Incubation of alpha-crystallin with DL-glyceraldehyde and arginine-modifying agents also enhances chaperone function, and we believe that the increased chaperone activity depends on the extent of arginine modification. Far- and near-UV circular dichroism spectra indicate modest changes in secondary and tertiary structure of MG-modified alpha-crystallin. LC MS/MS analysis of MG-modified alpha-crystallin following chymotryptic digestion revealed that R21, R49, and R103 in alphaA-crystallin were converted to argpyrimidine. 1,1'-Bis(4-anilino)naphthalene-5,5'-disulfonic acid binding, an indicator of hydrophobicity of proteins, increased in alpha-crystallin modified by low concentrations of MG (2-100 microM). MG similarly enhances chaperone function of another small heat shock protein, Hsp27. Our results show that posttranslational modification by a metabolic product can enhance the chaperone function of alpha-crystallin and Hsp27 and suggest that such modification may be a protective mechanism against environmental and metabolic stresses. Augmentation of the chaperone function of alpha-crystallin might have evolved to protect the lens from deleterious protein modifications associated with aging.
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