Microtubule-binding property of microtubule-associated protein 2 differs from that of microtubule-associated protein 4 and tau

The microtubule-binding domains of microtubule-associated protein (MAP) 2, MAP4, and tau are structurally similar [Aizawa, H., Emori, Y., Murofushi, H ., Kawasaki, H., Sakai., H.,and Suzuki, K. (1990) J. Biol. Chem. 265, 13849 -13855]. To compare the microtubule-binding mechanisms of the three MAPs, w e performed a quantitative competition analysis using the three MAPs and th e microtubule-binding domain fragment of MAP4 (PA(4)T fragment). The two-cy cled microtubule protein fraction from bovine brain contains MAP1, MAP2, MA P4, and tau. When an excess of the PA(4)T fragment was added to the microtu bule protein fraction, MAP4 and tau were completely released from the micro tubules, while MAP1 remained bound. MAP:! was only partially released from the microtubules. The competition between MAP2 and MAP4 was further analyze d using purified MAP2, the PA(4)T fragment, and tubulin. About half of the MAP2 was still bound to the microtubules, even in the presence of an excess amount of the PA(4)T fragment. The microtubule-binding mechanisms of MAP:! and MAP4 seem to be different, in spite of their similar primary structure s.