IBUPROFEN PROTECTS ALPHA-CRYSTALLIN AGAINST POSTTRANSLATIONAL MODIFICATION BY PREVENTING PROTEIN CROSS-LINKING

Posttranslational modification of bovine alpha-crystallin by D-erythro se-4-phosphate, fructose-6-phosphate, D-ribose-5-phosphate and carbamy lation using potassium cyanate induced the loss of chaperone-like acti vity, as assessed by gamma-crystallin aggregation. The presence of hig h-molecular-weight aggregates indicated that erythrosylated, fructosyl ated and carbamylated alpha-crystallins were modified by non-reducible cross-linking. In contrast, ribosylation of alpha-crystallin induced the formation of reducible cross-links. Analysis of ribosylated, eryth rosylated and carbamylated alpha-crystallin using non-denaturing acryl amide gels showed that the cross-linking did not sterically inhibit th e normal aggregate formation or alter the oligomerisation of the aggre gate. Co-incubation of ibuprofen in the presence of alpha-crystallin a nd the modifying agents protected the chaperone-like activity of alpha -crystallin, enabling the inhibition of gamma-crystallin aggregation. In addition, ibuprofen inhibited the formation of both reducible and n on-reducible cross-linked high-molecular-weight alpha-crystallin aggre gates. We show in this paper that ibuprofen can inhibit in vitro cross -linking events responsible for the loss of chaperone-like activity of alpha-crystallin and suggest that the protective effect of ibuprofen may be exerted by the binding of ibuprofen breakdown products to alpha -crystallin lysine groups, preventing posttranslational modification r esponsible for the loss of chaperone-like activity.