Enhancement of chaperone function of alpha-crystallin by methylglyoxal modification.
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.
Nagaraj
Ram H
RH
Department of Ophthalmology, Case Western Reserve University, Cleveland, Ohio 44106-5068, USA. nhr@po.cwru.edu
Oya-Ito
Tomoko
T
Padayatti
Pius S
PS
Kumar
Radhika
R
Mehta
Sachin
S
West
Karen
K
Levison
Bruce
B
Sun
Jian
J
Crabb
John W
JW
Padival
Anoop K
AK
D000426:Alcohol Dehydrogenase / Q000032:analysis / Q000378:metabolism; D000817:Anilino Naphthalenesulfonates / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001205:Ascorbic Acid / Q000737:chemistry / Q000494:pharmacology; D002417:Cattle; D002950:Citrate (si)-Synthase / Q000032:analysis / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000032:analysis / Q000378:metabolism; D007908:Lens, Crystalline / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D008875:Middle Aged; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism*; D009005:Monosaccharides / Q000494:pharmacology; D009952:Ornithine / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry / Q000494:pharmacology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011743:Pyrimidines / Q000032:analysis / Q000737:chemistry / Q000494:pharmacology; D011765:Pyruvaldehyde / Q000737:chemistry* / Q000494:pharmacology*; D038201:alpha-Crystallins / Q000737:chemistry* / Q000378:metabolism*
D000817:Anilino Naphthalenesulfonates; D007328:Insulin; D018832:Molecular Chaperones; D009005:Monosaccharides; D011743:Pyrimidines; D038201:alpha-Crystallins; C107313:argpyrimidine; D011765:Pyruvaldehyde; D001120:Arginine; D009952:Ornithine; D000426:Alcohol Dehydrogenase; D002950:Citrate (si)-Synthase; D008239:Lysine; D001205:Ascorbic Acid