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Human beta-crystallins modified by backbone cleavage, deamidation and oxidation are prone to associate
Zhongli Zhang1, David L Smith, Jean B Smith
1Department of Chemistry, University of Nebraska, Lincoln, NE 68588-0304, USA.
Experimental Eye Research
|August 9, 2003
Summary
Human beta-crystallins undergo various in vivo modifications, including deamidation and truncation, even before age 20. BetaB2-crystallin may help solubilize these modified proteins in aging eye lenses.
Area of Science:
- Ophthalmology
- Protein Biochemistry
- Molecular Biology
Background:
- Beta-crystallins are crucial lens proteins, but their study is hindered by isolation difficulties due to high homology and post-translational modifications.
- Age-related modifications lead to diverse molecular masses and acidities, complicating individual beta-crystallin analysis.
Purpose of the Study:
- To identify previously unknown in vivo post-translational modifications in human beta-crystallins.
- To investigate the role of beta-crystallin modifications and associations in lens protein solubility.
Main Methods:
- Isolation of human beta-crystallins using multi-step chromatography.
- Two-dimensional gel electrophoresis for separating and analyzing modified crystallins.
- Chromatographic behavior analysis to study protein complex formation.
Main Results:
- Identified numerous in vivo modifications: deamidations (except betaB3), truncations (betaA3, betaB1, betaA4), and oxidation of methionines/tryptophans.
- Most modifications occurred before age 20, with modest increases in older individuals (20-87 years).
- Modified beta-crystallins formed non-covalent complexes, with betaB2-crystallin potentially aiding solubility of heavily modified forms.
Conclusions:
- Human beta-crystallins undergo significant early-life post-translational modifications.
- BetaB2-crystallin's solubility and presence in complexes suggest a role in managing modified beta-crystallins.
- Beta-crystallin modifications and associations may contribute to their superior solubility compared to alpha- and gamma-crystallins in aging lenses.