alpha-Crystallin chaperone activity is reduced by calpain II in vitro and in selenite cataract

J Biol Chem. 1993 Sep 5;268(25):18844-9.

Abstract

This study reports the first demonstration of a marked reduction in alpha-crystallin chaperone activity in an experimental model of cataract, and the study implicates activation of the cysteine protease calpain II (EC 3.4.22.17) as the in vivo protease responsible for decreased chaperone activity. Chaperone activity of normal alpha-crystallin from lenses of young rats was assayed by measuring attenuation of heat-induced aggregation and scattering of beta L-crystallin. alpha-Crystallin from the nucleus of lenses with selenite cataract showed specific selective proteolysis, and chaperone activity was diminished. Proteolysis of alpha-crystallin from selenite cataract lenses was mimicked by incubating normal alpha-crystallin with calpain II, and this also resulted in loss of chaperone activity. Two-dimensional gel electrophoresis and peptide mapping were used to identify four partially degraded alpha A- and alpha B-crystallin polypeptides following incubation of normal alpha-crystallin with calpain. Similar partially degraded alpha A and alpha B polypeptides were found in selenite cataract. Previous experiments indicated that alpha-crystallin chaperone activity decreases because of removal of the COOH terminus. Our experiments support this observation and suggest that calpain proteolysis of alpha-crystallin at the COOH terminus may result in a loss of chaperone activity in selenite cataract.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Calpain / metabolism
  • Calpain / pharmacology*
  • Cataract / chemically induced
  • Cataract / metabolism*
  • Crystallins / chemistry
  • Crystallins / metabolism*
  • Electrophoresis, Gel, Two-Dimensional
  • Endopeptidases / metabolism
  • Hot Temperature
  • Light
  • Molecular Sequence Data
  • Peptide Fragments / metabolism
  • Peptide Mapping
  • Rats
  • Rats, Sprague-Dawley
  • Scattering, Radiation
  • Selenium*
  • Sodium Selenite
  • Trypsin / metabolism

Substances

  • Crystallins
  • Peptide Fragments
  • Endopeptidases
  • Trypsin
  • Calpain
  • Selenium
  • Sodium Selenite