Heat shock protein 70 of filarial parasite Setaria equina: Cloning, expression, and analysis of binding with diethylcarbamazine citrate.

Setaria equina heat shock protein (SeqHSP) 70 gene was characterized, cloned and expressed to recombinant protein (rSeqHSP70). The protein was tested for binding with an anti-filarial drug "diethylcarbamazine citrate (DEC)" by equilibrium dialysis method. Molecular docking was also used to determine the binding sites and residues of binding with DEC. The mice were immunized with the protein alone or bound to DEC. Serum IFN-γ levels in the immunized group with protein-drug complex were significantly higher (P < 0.05) than the protein-immunized group. Mouse anti-SeqHSP70 polyclonal IgG recognized 2 bands at 70 and 75 kDa in S. equina adult worm and human cancer cell lines (HepG2 and MCF-7) extracts. The proliferation assay for mice splenocytes revealed a potentiation and down-regulating effects in non-immunized and immunized groups, respectively with the drug-protein complex. The proliferation and IFN-γ assays for purified human NK cells indicated a potentiating effect of the drug-protein complex (DEC concentration is 50 µM) comparable to the protein. DEC at lower concentration (25 mM) could also show a significant increase (P < 0.05) in IFN-γ. From the results, DEC was postulated to induce conformational changes in the protein exposing more epitopes for NK cell binding and activation.