Peptides corresponding to the second repeated sequence in MAP-2 inhibit binding of microtubule-associated proteins to microtubules.

Bovine brain high molecular weight microtubule-associated proteins (MAPs) can be displaced from assembled tubules by peptides corresponding to the second of three nonidentical repeated sequences in mouse MAP-2. The octadecapeptide m2 (VTSKCGSLKNIRHRPGGG) can release MAP-1b from MAP-containing microtubules, and the extended second-sequence peptide m2' (VTSKCGSLKNIRHRPGGGRVK) displaces MAP-1a and MAP-1b as well as MAP-2a and MAP-2b. Peptides m2 and m2' stimulate tubulin polymerization in the absence of MAPs or microtubule-stabilizing agents, and m2' acts as a competitive inhibitor of radiolabeled MAP-2 binding. The dissociation constant for MAP-2 binding to taxol-stabilized tubules was 3.4 microM in the absence of m2' and 14 microM in the presence of 1.5 mM of the m2' peptide. We estimate that the inhibition constant for peptide m2' is about 0.5 mM, about 100 times lower than for the Km of MAP-2. These observations suggest that the second repeated sequence in MAP-2 may represent an important recognition site for MAP binding to microtubules and that other structural features within MAP-2 may reinforce the strength of MAP-microtubule interactions.