Expression of cloned beta-tubulin genes of Haemonchus contortus in Escherichia coli: interaction of recombinant beta-tubulin with native tubulin and mebendazole.

Two distinct beta-tubulin cDNA isotypes (beta 8-9 and beta 12-16) from Haemonchus contortus were expressed for the first time in Escherichia coli and characterised by their specific mebendazole (MBZ) binding and polymerization properties. Beta-tubulin was expressed without translational fusion to an E. coli sequence under the regulation of the tryptophan promoter in the pTrp2 vector. Beta-tubulin was produced in large amounts in insoluble 'inclusion bodies'. The inclusion bodies were purified and solubilised and the beta-tubulin renatured by treatment with urea followed by dilution with alkaline buffer and a shift to physiological pH. The yield was more than 10 mg of beta-tubulin per litre of cell culture. The recombinant tubulin produced was recognized in Western blot by specific anti-beta-tubulin antibodies. Tritiated MBZ binding to the recombinant H. contortus beta-tubulin was measured in the presence or absence of whole, tubulin-free or tubulin-rich extracts of H. contortus. Some [3H]MBZ high-affinity binding (HB) to 'pure' (no other eukaryotic protein present) beta 8-9 or beta 12-16 was observed. Enhanced high-affinity binding was observed when recombinant beta 8-9 or beta 12-16 were mixed and pre-incubated with whole supernatants or tubulin-enriched extracts from H. contortus. The enhancement was more than additive. Beta 12-16 bound more MBZ and caused a greater enhancement than beta 8-9. Mixing recombinant beta 8-9 or beta 12-16 with whole supernatants or tubulin-enriched fractions from H. contortus promoter polymerization at 37 degrees C. Use of 35S-labelled protein showed that the polymer contained recombinant tubulin. Western blot using specific anti-alpha-tubulin monoclonal antibodies showed that the polymer contained alpha-tubulin. Similarly the recombinant nematode beta-tubulin co-polymerized with tubulin from chicken brain. Our data suggest that the recombinant beta-tubulin can interact and copolymerize with parasite or chicken tubulin. Furthermore the interaction of recombinant nematode beta-tubulin with native tubulin and/or microtubule associated proteins (MAPs) resulted in the formation of high-affinity MBZ-binding sites. However, interaction of recombinant beta-tubulin with microtubule proteins from chicken brain did not result in the formation of high-affinity MBZ-binding sites.