title: Methionine sulfoxide reductase A (MsrA) restores alpha-crystallin chaperone activity lost upon methionine oxidation.
abstract: BACKGROUND
  Lens cataract is associated with protein oxidation and aggregation. Two proteins that cause cataract when deleted from the lens are methionine sulfoxide reductase A (MsrA) that repairs protein methionine sulfoxide (PMSO) oxidized proteins and alpha-crystallin which is a two-subunit (alphaA and alphaB) chaperone. Here, we tested whether PMSO formation damages alpha-crystallin chaperone function and whether MsrA could repair PMSO-alpha-crystallin.
  
  
  METHODS
  Total alpha-crystallin was oxidized to PMSO and evaluated by CNBr-cleavage and mass spectrometry. Chaperone activity was measured by light scattering using lysozyme as target. PMSO-alpha-crystallin was treated with MsrA, and repair was assessed by CNBr cleavage, mass spectrometry and recovery of chaperone function. The levels of alpha-crystallin-PMSO in the lenses of MsrA-knockout relative to wild-type mice were determined.
  
  
  RESULTS
  PMSO oxidation of total alpha-crystallin (met 138 of alphaA and met 68 of alphaB) resulted in loss of alpha-crystallin chaperone activity. MsrA treatment of PMSO-alpha-crystallin repaired its chaperone activity through reduction of PMSO. Deletion of MsrA in mice resulted in increased levels of PMSO-alpha-crystallin.
  
  
  CONCLUSIONS
  Methionine oxidation damages alpha-crystallin chaperone function and MsrA can repair PMSO-alpha-crystallin restoring its chaperone function. MsrA is required for maintaining the reduced state of alpha-crystallin methionines in the lens.
  
  
  CONCLUSIONS
  Methionine oxidation of alpha-crystallin in combination with loss of MsrA repair causes loss of alpha-crystallin chaperone function. Since increased PMSO levels and loss of alpha-crystallin function are hallmarks of cataract, these results provide insight into the mechanisms of cataract development and likely those of other age-related diseases.
authors.affiliation: Biomedical Sciences Department, Charles E. Schmidt College of Biomedical Science, Florida Atlantic University, Boca Raton, FL, USA.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Brennan
authors.forename: Wanda
authors.initials: W
authors.lastname: Lee
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Giblin
authors.forename: Larry L
authors.initials: LL
authors.lastname: David
authors.forename: Marc
authors.initials: M
authors.lastname: Kantorow
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D006801:Humans; D007908:Lens, Crystalline / Q000378:metabolism; D008715:Methionine / Q000737:chemistry / Q000378:metabolism*; D051150:Methionine Sulfoxide Reductases; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism / Q000502:physiology*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding; D021241:Spectrometry, Mass, Electrospray Ionization; D038201:alpha-Crystallins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*
chemical_list: D018832:Molecular Chaperones; D038201:alpha-Crystallins; D008715:Methionine; D010088:Oxidoreductases; D051150:Methionine Sulfoxide Reductases; C027219:methionine sulfoxide reductase