CHAPERONE ACTIVITY OF ALPHA-B-CRYSTALLIN SUPPRESSES TUBULIN AGGREGATION THROUGH COMPLEX-FORMATION

alpha B-Crystallin, one of the small heat shock proteins, is constitut ively expressed in lens as well as in nonlenticular tissues. It can fu nction as a molecular chaperone for other lens crystallins and some ot her proteins. Its nonocular function is unknown although some reported one of them is related to cytoskeletal networks and/or components. In the present study, we demonstrate the association of alpha B-crystall in with tubulin. Immunoprecipitation experiments using L6 myoblast cel l lysate with anti-alpha B-crystallin antibody resulted in the copreci pitation of alpha-tubulin, which was apparently temperature-dependent. Further, purified alpha B-crystallin prevented the turbidity developm ent of purified tubulin molecule at 37 degrees C in vitro. Sucrose gra dient centrifugation revealed that this chaperone activity was accompa nied by the formation of large complex of alpha B-crystallin and tubul in dimer. These results indicate that one of the nonlenticular functio ns of alpha B-crystallin may be the protection of tubulin subunits of microtubules.