The molecular chaperone alpha-crystallin inhibits UV-induced protein aggregation.
Solutions of gamma-crystallin, and various enzymes, at neutral pH and 24-26 degrees C, became turbid upon exposure to UV radiation at 295 or 308 nm. SDS-PAGE analysis revealed interchain cross-linking and aggregate formation compared to dark control solutions as reported previously. When alpha-crystallin was added to the protein solutions in stoichiometric amounts, UV irradiation resulted in significantly less turbidity than in the absence of alpha-crystallin. For example, addition of 0.5 mg of alpha-crystallin to 0.5 mg of gamma-crystallin in 1.0 ml solution yielded only 25% of the turbidity seen in the absence of alpha-crystallin. Addition of 2.0 mg of alpha-crystallin resulted in 20% of the turbidity. Given the molecular weights of alpha- and gamma-crystallin (about 800 kDa and 20 kDa, respectively), a gamma/alpha 1:1 weight ratio corresponds to a 40:1 molar ratio, and a gamma/alpha 1:4 weight ratio corresponds to a 10:1 molar ratio. Hence, the molar ratio of alpha-crystallin needed to effectively protect gamma-crystallin from photochemical opacification was gamma/alpha = n:1, where n was in the range 10-40. In terms of subunits, this ratio is gamma/alpha = 1:m, where m = 1-4. Thus, each gamma-crystallin molecule needs 1-4 alpha subunits for protection. Similar stoichiometries were observed for protection of the other proteins studied. The protection stems in part from screening of UV radiation by alpha-crystallin but more importantly from a chaperone effect analogous to that seen in thermal aggregation experiments.
Borkman
R F
RF
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta 30332, USA.
Knight
G
G
Obi
B
B
D000818:Animals; D002256:Carbonic Anhydrases / Q000528:radiation effects; D002417:Cattle; D003459:Crystallins / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004591:Electrophoresis, Polyacrylamide Gel; D004798:Enzymes / Q000528:radiation effects*; D005634:Fructose-Bisphosphate Aldolase / Q000528:radiation effects; D006358:Hot Temperature; D066298:In Vitro Techniques; D018832:Molecular Chaperones; D010751:Phosphopyruvate Hydratase / Q000528:radiation effects; D011489:Protein Denaturation / Q000528:radiation effects*; D013997:Time Factors; D014466:Ultraviolet Rays
D003459:Crystallins; D004798:Enzymes; D018832:Molecular Chaperones; D005634:Fructose-Bisphosphate Aldolase; D002256:Carbonic Anhydrases; D010751:Phosphopyruvate Hydratase