Methionine sulfoxide reductase A (MsrA) restores alpha-crystallin chaperone activity lost upon methionine oxidation.
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.
Brennan
Lisa A
LA
Biomedical Sciences Department, Charles E. Schmidt College of Biomedical Science, Florida Atlantic University, Boca Raton, FL, USA.
Lee
Wanda
W
Giblin
Frank J
FJ
David
Larry L
LL
Kantorow
Marc
M
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*
D018832:Molecular Chaperones; D038201:alpha-Crystallins; D008715:Methionine; D010088:Oxidoreductases; D051150:Methionine Sulfoxide Reductases; C027219:methionine sulfoxide reductase