Proteolysis by m-calpain enhances in vitro light scattering by crystallins from human and bovine lenses.
OBJECTIVE
To determine if proteolysis by the calcium-activated protease m-calpain (EC 34.22.17) enhances in vitro light scattering in crystallins from human and bovine lenses.


METHODS
Total soluble proteins from bovine, human, and rodent lenses, betaH crystallin, or recombinant betaB1 polypeptide were pre-incubated in the presence or absence of activated m-calpain. Heat-induced light scattering was assayed by measuring changes in optical density at 405 nm. Proteolysis and cleavage sites were detected by SDS-PAGE, two dimensional electrophoresis, and N-terminal Edman sequencing.


RESULTS
The in vitro cleavage sites produced by m-calpain on the N-termini of human betaB1, betaA3, and betaB2-crystallins were similar to some of those on bovine and rat crystallins. Proteolysis of alpha- and beta-crystallins was associated with enhanced, heat-induced light scattering by human and bovine lens proteins.


CONCLUSIONS
Proteolysis may be a contributing factor in the insolubilization of crystallins occurring during normal maturation of lens or during cataract formation in such species as man and cows.
Shih
M
M
Department of Oral Molecular Biology, Oregon Health Sciences University, Portland, OR 97201, USA.
David
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Lampi
K J
KJ
Ma
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Fukiage
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Azuma
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Shearer
T R
TR
D000595:Amino Acid Sequence; D000818:Animals; D002154:Calpain / Q000494:pharmacology*; D002417:Cattle; D003459:Crystallins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D006801:Humans; D007908:Lens, Crystalline / Q000187:drug effects* / Q000378:metabolism; D008027:Light; D008875:Middle Aged; D008969:Molecular Sequence Data; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D012542:Scattering, Radiation
D003459:Crystallins; D011994:Recombinant Proteins; D002154:Calpain