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Age-dependent deamidation of lifelong proteins in the human lens
Peter G Hains1, Roger J W Truscott
1Save Sight Institute, University of Sydney, Sydney, NSW, Australia.
Purpose:
Deamidation is a common posttranslational modification in human lens crystallins and may be a key factor in the age-related denaturation of such lifelong proteins. The aim of this study was to identify the sites of deamidation in older lenses.
Methods:
High-performance liquid chromatography/mass spectrometry of tryptic digests was used to identify sites of deamidation in the major human lens crystallins. Older normal and age-matched cataractous lenses were compared with fetal lenses.
Results:
Approximately equal numbers of glutamine and asparagine residues were deamidated in older lenses; however, the extent of deamidation of Asn was three times greater than that of Gln (Asn, 22.6% +/- 3.6%; Gln, 6.6% +/- 1.3%). Individual crystallins differed markedly in their extent of deamidation, and deamidated residues were typically localized within discrete regions of the polypeptides. A large percentage (42%) of the sites of deamidation were characterized by the presence of a basic amino acid one residue removed from the original Gln or Asn. At nine such sites, the extent of Asn deamidation averaged 50% in aged lenses. There were few differences in deamidation between crystallins of aged normal and nuclear cataractous lenses.
Conclusions:
Equal numbers of Asn and Gln residues are deamidated in crystallins from aged normal and cataractous lenses. Deamidation of Asn/Gln in lifelong proteins, such as those in the lens, may be governed to a significant degree by base-catalyzed processes.
Insights
Deamidation of asparagine (Asn) and glutamine (Gln) residues in human lens crystallins increases with age. This age-related modification, particularly of Asn, may be driven by base-catalyzed processes in lifelong proteins.
Area of Science:
- Biochemistry
- Proteomics
- Ophthalmology
Background:
- Deamidation is a common posttranslational modification in human lens crystallins.
- This modification is implicated in the age-related denaturation of lifelong proteins like crystallins.
Purpose of the Study:
- To identify specific sites of deamidation in human lens crystallins from older individuals.
- To compare deamidation patterns in normal aging lenses versus those with nuclear cataracts.
Main Methods:
- Utilized high-performance liquid chromatography/mass spectrometry (HPLC/MS) on tryptic digests of human lens crystallins.
- Compared deamidation sites in fetal, older normal, and age-matched cataractous lenses.
Main Results:
- Identified roughly equal numbers of deamidated asparagine (Asn) and glutamine (Gln) residues in older lenses.
- Observed a significantly higher extent of deamidation for Asn (22.6%) compared to Gln (6.6%).
- Found that deamidated residues often occurred near basic amino acids, with Asn deamidation reaching 50% at specific sites in aged lenses.
Conclusions:
- Asparagine and glutamine deamidation occur in crystallins from both aged normal and cataractous lenses.
- The deamidation of Asn/Gln in long-lived proteins like lens crystallins may be significantly influenced by base-catalyzed mechanisms.
