ALPHA-CRYSTALLIN SMALL HEAT-SHOCK PROTEIN HAS AUTOKINASE ACTIVITY

The alpha-crystallins (alphaA and alphaB) are major water-soluble proteins of the transparent eye lens that are expressed in a variety of tissues and can function as molecular chaperones. AlphaB-crystallin is also a small heat shock protein associated with numerous degenerative diseases and abnormal growth patterns. Previous experiments have shown that alphaA- and alphaB-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-P-32]ATP; the autophosphorylated products isoelectrically focus with the authentic phosphorylated forms of the alpha-crystallin polypeptides. Thus, the alphaA- and alphaB-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.