Cloning and characterization of cDNAs encoding beta-tubulin from Dirofilaria immitis and Onchocerca volvulus

β-Tubulin is the target for the benzimidazole anthelmintics. Unfortunately, none of these drugs is clinically useful against adult filariae. However, β-tubulin has been shown to be a target for antibody-based toxicity to Brugia pahangi. We cloned and characterized cDNAs encoding β -tubulin from 2 filariae, Dirofilaria immitis and Onchocerca volvulus, to explore possible explanations for benzimidazole insensitivity among adult filariae and the likelihood that epitopes of β-tubulin could be used as antigens for a broad-spectrum filarial vaccine. The proteins predicted by these cDNAs were almost identical to the β-tubulin previously reported from B. pahangi but were less similar to a β-tubulin cDNA from Onchocerca gibsoni. We cloned the genomic locus for the O. volvulus β-tubulin cDNA and compared its organization to the reported genomic loci for β-tubulin in B. pahangi and O. gibsoni. The comparison reinforces the conclusion that the published O. gibsoni gene is in a different family, possibly the (52 family previously described in B. pahangi. The substitution of tyr for phe at position 200 of β-tubulin is associated with benzimidazole resistance. All 4 filarial β-tubulins are predicted to encode phe at this position, suggesting that filarial β-tubulin is not inherently insensitive to the benzimidazoles. A monoclonal antibody that recognizes the COOH terminus of B. pahangi β-tubulin is lethal to this parasite in culture. The COOH terminal region is the most variable among the different isotypes of β -tubulin and distinguishes mammalian from nematode tubulins. This region is highly conserved in 3 of the filarial β-tubulins.