DMAP-85 - A TAU-LIKE PROTEIN FROM DROSOPHILA-MELANOGASTER LARVAE

Microtubule-associated proteins (MAPs) play major regulatory roles in the organization and integrity of the cytoskeletal network. Our main i nterest in this study was the identification and the analysis of struc tural and functional aspects of Drosophila melanogaster MAPs. A novel MAP with a relative molecular mass of 85 kDa from Drosophila larvae wa s found associated with taxol-polymerized microtubules. In addition, t his protein bound to mammalian tubulin in an overlay assay and coassem bled with purified bovine brain tubulin in microtubule sedimentation e xperiments. The estimated stoichiometry of 85-kDa protein versus tubul in in the polymers was 1:5.3 +/- 0.2 mol/mol. It was shown that the 85 -kDa protein bound specifically to an affinity column of Sepharose-bet a II-(422-434) tubulin peptide, which contains the sequence of the MAP binding domain on pll-tubulin. Affinity-purified 85-kDa protein enhan ced microtubule assembly in a concentration-dependent manner. This eff ect was significantly decreased by the presence of the beta II-(422-43 4) peptide in the assembly assays, thus confirming the specificity of the 85-kDa protein interaction with the C-terminal domain on tubulin. Furthermore, this protein also exhibited a strong affinity for calmodu lin, based on affinity chromatographic assays. Monoclonal and polyclon al anti-tau antibodies, including sequence-specific probes that recogn ize repeated microtubule-binding motifs on tau, MAP-2, and MAP-4 and s pecific N-terminal sequences of tau, cross-reacted with the 85-kDa pro tein from Drosophila larvae. These results suggest that tau and Drosop hila 85-kDa protein share common functional and structural epitopes. W e have named this protein as DMAP-85 for Drosophila MAP. The finding o n a Drosophila protein with functional homology and structural similar ities to mammalian tau opens new perspectives to understand the cellul ar roles of MAPs.