Chaperone activity of alpha B-crystallin suppresses tubulin aggregation through complex formation

alpha B-Crystallin, one of the small heat shock proteins, is constitutively expressed in lens as well as in nonlenticular tissues. It can function as a molecular chaperone for other lens crystallins and some other 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-crystallin with tubulin. Immunoprecipitation experiments using L6 myoblast cell lysate with anti-alpha B-crystallin antibody resulted in the coprecipitation of alpha-tubulin, which was apparently temperature-dependent. Further, purified alpha B-crystallin prevented the turbidity development of purified tubulin molecule at 37 degrees C in vitro. Sucrose gradient centrifugation revealed that this chaperone activity was accompanied by the formation of large complex of alpha B-crystallin and tubulin dimer. These results indicate that one of the nonlenticular functions of alpha B-crystallin may be the protection of tubulin subunits of microtubules.