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Keywords:

  • α-crystallin;
  • heat-shock protein;
  • actin;
  • phosphorylation;
  • stabilization

α-crystallin, a major lens protein of approximately 800 kDa with subunits of about 20 kDa has previously been shown to act as a chaperone protecting other proteins from stress-induced damage and to share sequence similarity with small heat-shock proteins, sHsp. It is now demonstrated that this chaperone effect extends to protection of the intracellular matrix component actin. It was found that the powerful depolymerization effect of cytochalasin D could be almost completely blocked by α-crystallin, αA-crystallin or αB-crystallin. However, phosphorylation of α-crystallin markedly decreased its protective effect. It is suggested that phosphorylation of α-crystallin may contribute to changes in actin structure observed during cellular remodeling that occurs with the terminal differentiation of a lens epithelial cell to a fiber cell and contributes to cellular remodeling in other cell types that contain α-crystallin species. This communication presents biochemical evidence clearly demonstrating that α-crystallin is involved in actin polymerization-depolymerization dynamics.

It is also shown that α-crystallin prevented heat-induced aggregation of actin filaments. α-crystallin was found to stabilize actin polymers decreasing dilution-induced depolymerization rates up to twofold while slightly decreasing the critical concentration from 0.23 μM to 0.18 μM. Similar results were found with either α-crystallin or its purified subunits αA-crystallin and αB-crystallin. In contrast to the experiments with cytochalasin D, phosphorylation had no effect. There does not appear to be an interaction between α-crystallin and actin monomers since the effect of α-crystallin in enhancing actin polymerization does not become apparent until some polymerization has occurred. Examination of the stoichiometry of the α-crystallin effect indicates that 2-3 α-crystallin monomers/actin monomer give maximum actin polymer stabilization.