Alpha-crystallin/small heat shock protein has autokinase activity.
The alpha-crystallins (alpha A and alpha B) are major water-soluble proteins of the transparent eye lens that are expressed in a variety of tissues and can function as molecular chaperones. alpha B-crystallin is also a small heat shock protein associated with numerous degenerative diseases and abnormal growth patterns. Previous experiments have shown that alpha A-and alpha B-crystallin are phosphorylated on specific serine residues by a cAMP-dependent pathway. Here we provide evidence that either total bovine alpha-crystallin or its isolated polypeptides can autophosphorylate serine by a cAMP-independent mechanism in the presence of Mg2+ and [gamma-32P]ATP; the autophosphorylated products isoelectrically focus with the authentic phosphorylated forms of the alpha-crystallin polypeptides. Thus, the alpha A- and alpha B-crystallin/small heat shock protein polypeptides are enzyme-crystallins which may be involved in metabolic pathways important for the development, maintenance, or pathology of the lens and other tissues.
Kantorow
M
M
Laboratory of Molecular and Developmental Biology, National Eye Institute, National Institutes of Health, Bethesda, MD 20892.
Piatigorsky
J
J
D000818:Animals; D002417:Cattle; D003459:Crystallins / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D007526:Isoelectric Point; D007908:Lens, Crystalline / Q000201:enzymology*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*
D003459:Crystallins; D006360:Heat-Shock Proteins; D010768:Phosphoserine; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases