EXPRESSION OF BIOACTIVE FUSION PROTEINS OF E. COLI HEAT-LABILE TOXIN B SUBUNIT AND SYNAPSIN PEPTIDES

摘要

Pentameric B subunit of E. coli heat-labile toxin (LTB) mediates holotoxin binding to host cell membranes and has been used as efficient mucosal carrier of chemically or genetically coupled antigens. We constructed two recombinant hybrid molecules by fusing the N-terminal of C (residues 113-308) and ABC (residues 1-308) domains of rat synapsin to the C-terminus of LTB. Both LTBSC and LTBSABC fusion proteins were inductively expressed as cytoplasmic inclusion bodies in E. coli and then purified by affinity chromatography on Ni-agarose under denaturant conditions. For in vitro refolding and oligomerization of the hybrid proteins dialysis and dilution were assayed to decrease denaturant concentration. We examined the effect of several conditions regarding redox environment and presence of L-arginine in refolding buffer. About 97 % of LTBSABC and 90% of LTBSC were recovered soluble in 0.05 M Tris buffer pH 8 containing 2 M urea. Both of them retained the ability to bind to GM1 receptor in an enzyme-linked immunosorbent assay. Also LTBSC induced oral tolerance when fed to rats before active immunization as it was shown by inhibition of the specific DTH response and in vivo and in vitro cell proliferation. These results strongly suggest that these fusion proteins are suitable for exploring mucosal adjuvant activity in autoimmune disorders involving antigens from central nervous system.