CHAPERONE-LIKE ACTIVITY OF TUBULIN

Tubulin, a ubiquitous protein of eukaryotic cytoskeleton, is a buildin g block unit of microtubule. Although several cellular processes are k nown to be mediated through the tubulin-microtubule system, the partic ipation of tubulin or microtubule in protein folding path way has not yet been reported. Here we show that goat brain tubulin has some funct ions and features similar to many known molecular chaperones. Substoic hiometric amounts of tubulin can suppress the non-thermal and thermal aggregation of a number of unrelated proteins such as insulin, equine liver alcohol dehydrogenase, and soluble eye lens proteins containing beta- and gamma-crystallins. This chaperone-like activity of tubulin b ecomes more pronounced as temperature increases. Aging of tubulin solu tion at 37 degrees C also enhances its chaperone-like activity. Tubuli n loses its chaperone-like activity upon removal of its flexible hydro philic C-terminal tail. These results suggest that both electrostatic and hydrophobic interactions are important in substrate binding by tub ulin and that the negatively charged C-terminal tails play a crucial r ole for its chaperone-like activity.