Enhancement of chaperone function of alpha-crystallin by methylglyoxal modification

Biochemistry. 2003 Sep 16;42(36):10746-55. doi: 10.1021/bi034541n.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alcohol Dehydrogenase / analysis
  • Alcohol Dehydrogenase / metabolism
  • Anilino Naphthalenesulfonates / analysis
  • Anilino Naphthalenesulfonates / chemistry
  • Anilino Naphthalenesulfonates / metabolism
  • Animals
  • Arginine / analogs & derivatives
  • Arginine / pharmacology
  • Ascorbic Acid / chemistry
  • Ascorbic Acid / pharmacology
  • Cattle
  • Citrate (si)-Synthase / analysis
  • Citrate (si)-Synthase / metabolism
  • Humans
  • Insulin / analysis
  • Insulin / metabolism
  • Lens, Crystalline / chemistry
  • Lysine / chemistry
  • Middle Aged
  • Molecular Chaperones / chemistry*
  • Molecular Chaperones / metabolism*
  • Monosaccharides / pharmacology
  • Ornithine / analogs & derivatives*
  • Ornithine / analysis
  • Ornithine / chemistry
  • Ornithine / pharmacology
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Pyrimidines / analysis
  • Pyrimidines / chemistry
  • Pyrimidines / pharmacology
  • Pyruvaldehyde / chemistry*
  • Pyruvaldehyde / pharmacology*
  • alpha-Crystallins / chemistry*
  • alpha-Crystallins / metabolism*

Substances

  • Anilino Naphthalenesulfonates
  • Insulin
  • Molecular Chaperones
  • Monosaccharides
  • Pyrimidines
  • alpha-Crystallins
  • argpyrimidine
  • Pyruvaldehyde
  • Arginine
  • Ornithine
  • Alcohol Dehydrogenase
  • Citrate (si)-Synthase
  • Lysine
  • Ascorbic Acid