Enhancement of Chaperone Function of -Crystallin by Methylglyoxal Modification
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- 作者：Ram H. Nagaraj ; Tomoko Oya-Ito ; Pius S. Padayatti ; Radhika Kumar ; Sachin Mehta ; Karen West ; Bruce Levison ; Jian Sun ; John W. Crabb ; and Anoop K. Padival
- 刊名：Biochemistry
- 出版年：2003
- 出版时间：September 16, 2003
- 年：2003
- 卷：42
- 期：36
- 页码：10746 - 10755
- 全文大小：212K
- 年卷期：v.42,no.36(September 16, 2003)
- ISSN：1520-4995
文摘
The molecular chaperone function of 
-crystallin in the lens prevents the aggregation andinsolubilization of lens proteins that occur during the process of aging. We found that chemical modificationof -crystallin by a physiological -dicarbonyl compound, methylglyoxal (MG), enhances its chaperonefunction. Protein-modifying sugars and ascorbate have no such effect and actually reduce chaperonefunction. Chaperone assay after immunoprecipitation or with immunoaffinity-purified argpyrimidine--crystallin indicates that 50-60% of the increased chaperone function is due to argpyrimidine-modifiedprotein. Incubation of -crystallin with DL-glyceraldehyde and arginine-modifying agents also enhanceschaperone function, and we believe that the increased chaperone activity depends on the extent of argininemodification. Far- and near-UV circular dichroism spectra indicate modest changes in secondary andtertiary structure of MG-modified -crystallin. LC MS/MS analysis of MG-modified -crystallin followingchymotryptic digestion revealed that R21, R49, and R103 in A-crystallin were converted to argpyrimidine.1,1'-Bis(4-anilino)naphthalene-5,5'-disulfonic acid binding, an indicator of hydrophobicity of proteins,increased in -crystallin modified by low concentrations of MG (2-100 
M). MG similarly enhanceschaperone function of another small heat shock protein, Hsp27. Our results show that posttranslationalmodification by a metabolic product can enhance the chaperone function of -crystallin and Hsp27 andsuggest that such modification may be a protective mechanism against environmental and metabolic stresses.Augmentation of the chaperone function of -crystallin might have evolved to protect the lens fromdeleterious protein modifications associated with aging.
-crystallin in the lens prevents the aggregation andinsolubilization of lens proteins that occur during the process of aging. We found that chemical modificationof -crystallin by a physiological -dicarbonyl compound, methylglyoxal (MG), enhances its chaperonefunction. Protein-modifying sugars and ascorbate have no such effect and actually reduce chaperonefunction. Chaperone assay after immunoprecipitation or with immunoaffinity-purified argpyrimidine--crystallin indicates that 50-60% of the increased chaperone function is due to argpyrimidine-modifiedprotein. Incubation of -crystallin with DL-glyceraldehyde and arginine-modifying agents also enhanceschaperone function, and we believe that the increased chaperone activity depends on the extent of argininemodification. Far- and near-UV circular dichroism spectra indicate modest changes in secondary andtertiary structure of MG-modified -crystallin. LC MS/MS analysis of MG-modified -crystallin followingchymotryptic digestion revealed that R21, R49, and R103 in A-crystallin were converted to argpyrimidine.1,1'-Bis(4-anilino)naphthalene-5,5'-disulfonic acid binding, an indicator of hydrophobicity of proteins,increased in -crystallin modified by low concentrations of MG (2-100 M). MG similarly enhanceschaperone function of another small heat shock protein, Hsp27. Our results show that posttranslationalmodification by a metabolic product can enhance the chaperone function of -crystallin and Hsp27 andsuggest that such modification may be a protective mechanism against environmental and metabolic stresses.Augmentation of the chaperone function of -crystallin might have evolved to protect the lens fromdeleterious protein modifications associated with aging.