DMAP-85: A τ-Like Protein from Drosophila melanogaster Larvae

Abstract: Microtubule-associated proteins (MAPs) play major regulatory roles in the organization and integrity of the cytoskeletal network. Our main interest in this study was the identification and the analysis of structural and functional aspects of Drosophila melanogaster MAPs. A novel MAP with a relative molecular mass of 85 kDa from Drosophila larvae was found associated with taxol-polymerized microtubules. In addition, this protein bound to mammalian tubulin in an overlay assay and coassembled with purified bovine brain tubulin in microtubule sedimentation experiments. The estimated stoichiometry of 85-kDa protein versus tubulin 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-βII-(422–434) tubulin peptide, which contains the sequence of the MAP binding domain on βII-tubulin. Affinity-purified 85-kDa protein enhanced microtubule assembly in a concentration-dependent manner. This effect was significantly decreased by the presence of the βII-(422–434) 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 calmodulin, based on affinity chromatographic assays. Monoclonal and polyclonal anti-τ antibodies, including sequence-specific probes that recognize repeated microtubule-binding motifs on τ, MAP-2, and MAP-4 and specific N-terminal sequences of τ, cross-reacted with the 85-kDa protein from Drosophila larvae. These results suggest that τ and Drosophila 85-kDa protein share common functional and structural epitopes. We have named this protein as DMAP-85 for Drosophila MAP. The finding on a Drosophila protein with functional homology and structural similarities to mammalian τ opens new perspectives to understand the cellular roles of MAPs.