alpha-crystallin prevents irreversible protein denaturation and acts cooperatively with other heat-shock proteins to renature the stabilized partially denatured protein in an ATP-dependent manner.
alpha-Crystallin, a major lens protein of approximately 800 kDa with subunits of approximately 20 kDa has previously been shown to act as a chaperone protecting other proteins from stress-induced aggregation. Here it is demonstrated that alpha-crystallin can bind to partially denatured enzymes at 42-43 degrees C and prevent their irreversible aggregation, but cannot prevent loss of enzyme activity. However, the alpha-crystallin-bound enzymes regain activity on interaction with other chaperones. The data indicate that the re-activated enzymes are no longer associated with the alpha-crystallin, and ATP is required for re-activation. When inactive luciferase bound to alpha-crystallin was treated with reticulocyte lysate, a rich source of chaperones, up to 60% of the original luciferase activity could be recovered. Somewhat less re-activation was observed when the alpha-crystallin-bound enzyme was treated with heat-shock protein (HSP)70, HSP40, HSP60 and an ATP-generating system. Similar results were also obtained with citrate synthase. The overall results suggest that alpha-crystallin acts to stabilize denaturing proteins so that they can later be re-activated by other chaperones.
Wang
K
K
Department of Ophthalmology, Columbia University, New York, USA. kw32@columbia.edu
Spector
A
A
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D018834:Chaperonin 60 / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003459:Crystallins / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D007908:Lens, Crystalline / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D010766:Phosphorylation; D011489:Protein Denaturation; D020673:Protein Renaturation; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D013552:Swine; D013696:Temperature; D013997:Time Factors; D014462:Ultrafiltration
D018834:Chaperonin 60; D003459:Crystallins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D000255:Adenosine Triphosphate; D008156:Luciferases; D002950:Citrate (si)-Synthase