Calpain II induced insolubilization of lens beta-crystallin polypeptides may induce cataract.
Addition of calpain II (EC 3.4.22.17) to soluble proteins from 10-day-old rat lens caused an increase in turbidity and production of water-insoluble protein. The insolubilization increased with higher concentrations of both lens protein and calpain II, it could be prevented by the cysteine protease inhibitor E-64; it required at least 0.5 mM Ca2+, it was limited to 6% of the soluble protein present and resulted from precipitation of proteolyzed beta-crystallin polypeptides. When compared by two-dimensional electrophoresis, the insoluble beta-crystallin polypeptides produced by calpain II were similar to insoluble beta-crystallin polypeptides found in cataractous lenses. Trypsin also caused insolubilization of beta-crystallin polypeptides, but these polypeptides were unlike polypeptides produced during cataract formation. These data suggested that the loss of solubility was due to a specific removal of N/or C-terminal extensions from beta-crystallin polypeptides by calpain II, and that a similar process may occur in vivo during cataract formation. It is hypothesized that the insoluble protein produced by calpain II causes cataract by increasing light scatter in the lens.
David
L L
LL
Department of Biochemistry, School of Dentistry, Oregon Health Sciences University, Portland 97201.
Wright
J W
JW
Shearer
T R
TR
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002386:Cataract / Q000209:etiology*; D002851:Chromatography, High Pressure Liquid; D003459:Crystallins / Q000737:chemistry / Q000378:metabolism*; D066298:In Vitro Techniques; D007908:Lens, Crystalline / Q000378:metabolism; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry; D051381:Rats; D012995:Solubility
D003459:Crystallins; D010446:Peptide Fragments; D002154:Calpain; D002118:Calcium