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Identification and characterization of post-translational modifications in human lens beta crystallins during the aging process

Zhongli Zhang, University of Nebraska - Lincoln


The major function of human lens is to focus the incident light on the retina without light scattering. The transparency and the precise refraction depend on the close packing of water-soluble structural proteins, called crystallins. Crystallins have undergone throughout the whole life the post-translational modifications, which are proposed to cause cataract. The β-crystallins can be categorized into acidic β-crystallins (βA1, βA3, and βA4) and basic β-crystallins (βB1, βB2, and βB3). The post-translational modifications have made the characterization of β-crystallins more complicated. The age-related modifications in β-crystallin subunits, which might provide information in explanation of relationship between aging process and cataractogenesis, have been of interest to lens investigators. This study is a comprehensive investigation of modifications in β-crystallin subunits from adult lenses. ^ Because of high sequence homology and extensive modifications, only partial separation of β-crystallins in adult lenses was obtained using reversed phase and ion exchange chromatography. The separation of β-crystallins and their modified products from adult lenses was remarkably improved by combination of reversed phase HPLC and two-dimensional gel electrophoresis. The in-situ tryptic digestion followed by on-line LC-MS/MS has demonstrated that βB2 was resistant to modification and might have solubilizing influence on other β-crystallins. Most βB1 showed degradation products missing 15–43 N-terminal residues in adult lenses, regardless of age. Age-related increase in oxidation at methionine/tryptophan and deamidation at glutamine/asparagine in βB1 was also detected. Most βA3 were present as βA3 (23–215) and their oxidized and deamidated forms. Loss of 26 N-terminal residues was observed in βA3 co-eluting with other β-crystallins in βB1 and βA4 fraction. Loss of 54 N-terminal residues was detected in aged lenses. Age-related increase in oxidation at methionine and deamidation at glutamine or asparagine in βA3 was also detected. Unlike the observation in previous reports, in which the βA4 was present as intact form, N-terminal and internal truncation were detected in βA4 from young adult lenses. As the lens aged, C-terminal truncation of βA4 started to occur in aged lenses. ^

Subject Area

Chemistry, Analytical|Chemistry, Biochemistry

Recommended Citation

Zhang, Zhongli, "Identification and characterization of post-translational modifications in human lens beta crystallins during the aging process" (2001). ETD collection for University of Nebraska - Lincoln. AAI3000467.