A new derivatizing agent, trimethylammoniopropyl methanethiosulphonate, is efficient for preparation of recombinant brain-derived neurotrophic factor from inclusion bodies.

Derivatization with trimethylammoniopropyl methanethiosulphonate (TAPS-sulphonate) enabled brain-derived neurotrophic factor (BDNF) to be prepared efficiently from Escherichia coli inclusion bodies. Reduced BDNF obtained from inclusion bodies solubilized by urea and reduced by dithiothreitol was suggested to form a complex with itself or with other compounds such as lipids. It could hardly be adsorbed on to cation-exchange resin for partial purification prior to a refolding reaction. Reversible derivatization of cysteine residues was tested as a method of dissociating BDNF from such complexes. However, even if a methyl or aminoethyl group was introduced, BDNF could not be dissociated readily. Derivatization with TAPS-sulphonate brought about good dissociation of BDNF, and more than 50% adsorbed on to the cation-exchange resin. BDNF derivatized with TAPS-sulphonate refolded well, and the refolded samples showed the same biological activity as purified BDNF. Derivatization with TAPS-sulphonate would increase the intermolecular repulsion of BDNF, due to the positively charged character of the quaternized amine, and inhibit complex formation. Thus, TAPS-sulphonate is effective for the preparation of BDNF under denatured conditions.