In vitro dephosphorylation of alpha-crystallin is dependent on the state of oligomerization.
alphaA- and alphaB-crystallin, members of the small heat shock protein family, are present in lens cell extracts as large aggregates. Both alpha-crystallins are found partially phosphorylated. This study tests the ability of five phosphatases (protein phosphatase PP1, PP2A, PP2B, alkaline and acid phosphatases) to dephosphorylate alphaA- and alphaB-crystallin in vitro. Activity of a phosphatase was dependent on the size of the aggregate. Each of the phosphatases tested showed different specificity and efficiency towards alphaA- and alphaB-crystallins, which depended on the oligomeric state of the alpha-crystallin aggregate. Alkaline phosphatase dephosphorylated both alphaA- and alphaB-crystallin. The reaction was faster when alpha-crystallin was in a tetrameric form. PP2A dephosphorylated primarily alphaA-crystallin but only after the conversion of alpha-crystallin to tetramers. PP1 and PP2B did not dephosphorylate either alphaA- or alphaB-crystallins present as large aggregates but could not be tested on the lower molecular weight form of alphaA-crystallin. Acid phosphatase dephosphorylated both alphaA- and alphaB-crystallin. The results suggest that an important relationship exists between the structure of alpha-crystallin and its level of phosphorylation in the cell.
Moroni
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M
Laboratory of Mechanisms of Ocular Diseases, National Eye Institute, National Institutes of Health, 9000 Rockville Pike, Bldg. 6, Rm. 235, 20892, Bethesda, MD, USA.
Garland
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D
D000135:Acid Phosphatase / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D019703:Calcineurin / Q000378:metabolism; D002417:Cattle; D002850:Chromatography, Gel; D003459:Crystallins / Q000737:chemistry / Q000378:metabolism*; D003840:Deoxycholic Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007525:Isoelectric Focusing; D007908:Lens, Crystalline / Q000737:chemistry; D046911:Macromolecular Substances; D008970:Molecular Weight; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding / Q000502:physiology; D013379:Substrate Specificity
D003459:Crystallins; D046911:Macromolecular Substances; D003840:Deoxycholic Acid; D000469:Alkaline Phosphatase; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D000135:Acid Phosphatase; D010744:Phosphoric Monoester Hydrolases