Expression and secretion of malarial parasite beta-tubulin in Bacillus brevis

Microtubule inhibitors are active against the human malarial parasite Plasmodium falciparum, but whether these drugs actually interact with parasite tubulins is not known. It has not previously been possible to produce mg quantities of isolated, soluble tubulin subunits for drug-binding experiments. A cDNA encoding P falciparum beta-tubulin was expressed and the protein secreted in Bacillus brevis. With the addition of EGTA to the culture medium, which increases shedding of proteins from the cell surface, up to 2 mg/l recombinant beta-tubulin was obtained in supernatants. It is not clear why B brevis is able to secrete this normally cytoplasmic protein, but the secretion levels of recombinant proteins may be related to the net charge of the first few residues of the mature polypeptide.