alphaB-Crystallin-coated MAP microtubule resists nocodazole and calcium-induced disassembly.

αB-Crystallin, one of the small heat-shock proteins, is constitutively expressed in various tissues including the lens of the eye. It has been suggested that αB-crystallin provides lens transparency but its function in nonlenticular tissues is unknown. It has been reported that αB-crystallin is involved in the stabilization and the regulation of cytoskeleton, such as intermediate filaments and actin. In this study, we investigate the possibility whether αBcrystallin interacts with the third cytoskeleton component, microtubules (MTs). First, we precisely observed the cellular localization of αB-crystallin and MT networks in L6E9 myoblast cells and found a striking coincidence between them. MTs reconstituted from cell lysate contained αB-crystallin. Electron micrographs clearly showed direct interactions of purified αB-crystallin with the surface of microtubule-associated proteins (MAPs) attached to MTs. Purified αB-crystallin bound to MAPMTs in a concentration-dependent manner. However, αBcrystallin did not bind MTs reconstituted from purified tubulin. Finally, we observed that αB-crystallin increased the resistance of MTs to depolymerization in cells and in vitro. Taken together, these results suggest that one of the functions of αB-crystallin is to bind MTs via MAP(s) and to give the MTs resistance to disassembly. Summary