Purpose. To compare the sites where the N-terminal extensions of βBl and βA3crystallins are cleaved in human, rat, and bovine lenses to determine if similar proteolytic activities are present in the lenses of each species. Methods. The partial sequence conservation of βB l and βA3 N-terminal extensions in rat, human, and bovine species, and the differential susceptibilities of these regions to proteolytic processing provide information regarding proteolytic activity in the lenses of each species. The soluble proteins from newborn human, two-week-old rat, and fetal calf lenses were separated by two-dimensional electrophoresis and the N-terminaf cleavage sites in βBl and βA3 in each species were determined by Edman sequencing. The cleavage sites occurring in vivo were then compared to the cleavage sites produced by incubation of lens protein from each species with the protease calpain II. Results- The N-tcrminal extensions of βB 1 and βA3-crystallins from all three species were susceptible to proteolytic processing. The major proteolytic product of βBl in human and bovine lens resulted from the removal of approximately 15 residues from the N-terminal extensions. Similar forms of human and bovine βA3 were also found, resulting from the removal of 22 residues from the N-terminal extensions. In contrast, the predominate forms of modified rat βBl and βA3 resulted from the removal of 48 and 11 residues, respectively. The cleavage of bovine βA3 was partially similar to the cleavage of rat βA3, since βA3 (-11) was also observed. While the protease calpain II could remove approximately 48 residues from rat and human βBl and approximately 11 residues from βA3 in all three species, it was unable to produce βBl (-15), or a distinct form of βA3 (-22) in any species. Conclusions. Calpain II may be the predominate protease of young rat lens, but no evidence for calpain II activation was found in young human lens. Human lenses appear to exhibit an unidentified proteolytic activity. Calf lens may be a suitable source to characterize this major crystallinolytic activity of young human lens.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience