Protein‐kinase‐C‐catalyzed phosphorylation of the microtubule‐binding domain of microtubule‐associated protein 2 inhibits its ability to induce tubulin polymerization

Abstract

It has previously been demonstrated that microtubule-associated protein 2 (MAP2) is a good substrate for the purified protein kinase C [Tsuyama, S., Bramblett, C. T., Huang, K.-P. & Flavin, M. (1986) J. Biol. Chem. 261, 4110–4116; Akiyama, T., Nishida, E., Ishida, J., Saji, N., Ogawara, H., Hoshi, M., Miyata, Y. & Sakai, H. (1986) J. Biol. Chem. 261, 15648–15651]. We have shown here that phosphorylation of MAP2, catalyzed by protein kinase C, reduces the ability to induce tubulin polymerization. MAP2 is divided into two domains by digestion with α-chymotrypsin; the microtubule-binding and the non-binding (projection) domains. The limited chymotryptic digestion following phosphorylation of MAP2 by protein kinase C has shown that both the domains of MAP2 were phosphorylated by protein kinase C, 50–60% of the incorporated phosphates being detected in the microtubule-binding domain. Polypeptide fragments, containing the microtubule-binding domain of MAP2 were purified by DEAE-cellulose column chromatography after chymotryptic digestion of MAP2. The purified microtubule-binding fragments were competent to polymerize tubulin, and served as good substrates for protein kinase C. The phosphorylation of the microtubule-binding fragments by protein kinase C reduced their ability to induce tubulin polymerization. These results suggest that the ability of MAP2 to induce tubulin polymerization is inhibited by phosphorylation of the microtubule-binding domain catalyzed by protein kinase C.