TUBULIN DOMAINS FOR THE INTERACTION OF MICROTUBULE-ASSOCIATED PROTEINDMAP-85 FROM DROSOPHILA-MELANOGASTER

The interaction of microtubule associated proteins (MAPs) with the mic rotubule system has been characterized in depth in neuronal cells from various mammalian species. These proteins interact with well-defined domains within the acidic tubulin carboxyl-terminal regulatory region. However, there is little information on the mechanisms of MAPs-tubuli n interactions in nonmammalian systems. Recently, a novel tau-like pro tein designated as DMAP-85 has been identified in Drosophila melanogas ter, and the regulation of its interactions with cytoskeletal elements was analyzed throughout different developmental stages of this organi sm. In this report, the topographic domains involved in the binding of DMAP-85 with tubulin heterodimer were investigated. Affinity chromato graphy of DMAP-85 in matrixes of taxol-stabilized microtubules showed the reversible interaction of DMAP-85 with domains on the microtubular surface. Co-sedimentation studies using the subtilisin-treated tubuli n (S-tubulin) indicated the lack of association of DMAP-85 to this tub ulin moiety. Moreover, studies on affinity chromatography of the purif ied 4 kDa C-terminal tubulin peptide bound to an affinity column, conf irmed that DMAP-85 interacts directly with this regulatory domain on t ubulin subunits. Further studies on sequencial affinity chromatography using a calmodulin affinity column followed by the microtubule column confirmed the similarities in the interaction behavior of DMAP-85 wit h that of tau. DMAP-85 associated to both calmodulin and the microtubu lar polymer. These studies support the idea that the carboxyl-terminal region on tubulin constitutes a common binding domain for most microt ubule-interacting proteins.