Purpose. To determine if limited proteolysis of β-crystallins is associated with insolubilization of proteins in rat lens during maturation and to test if the protease, calpain II, is involved. Methods. Soluble and insoluble lens proteins from 4-day-old to 4-month-old rat lens cortexes and nuclei were separated by two-dimensional electrophoresis. The insoluble proteins from 4-month-old nuclei were electroblotted and the NH2 termini of proteins sequenced. Cleavage sites appearing at 4 months of age were compared to cleavage sites produced by purified calpain II and to cleavage sites appearing in cataracts induced by selenite in vivo or in lenses cultured with calcium ionophore A23187 or diamide. Results. Insolubilization of more than 50% of proteins occurred in the nucleus of the transparent rat lens by 4 months of age. The insoluble protein that formed contained an abundance of partially degraded β-crystallin polypeptides missing portions of their NH2 terminal extensions. In contrast, these truncated β-crystallins were largely absent from both the cortex and soluble fraction of the nucleus. The cleavage sites in the insoluble β-crystallins appearing during maturation in the lens nucleus were similar to cleavage sites produced by purified calpain II and also similar to cleavage sites appearing in the insoluble protein of cataractous lenses. Conclusions. These results suggest that proteolysis of β-crystallins by the protease calpain II contributes to protein insolubilization during lens maturation and that acceleration of this insolubilization process is associated with cataract formation in rodent lenses.
|Original language||English (US)|
|Number of pages||9|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - 1994|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience