Expression, purification, and functional characterisation of flagellin, a TLR5-ligand.

Flagellin, a Toll-like receptor 5 (TLR5)-ligand, is known for its activities like adjuvant, induction of pro-inflammatory cytokines and innate immunity. In this context, fliC gene of Salmonella Typhimurium was cloned into pET32a expression plasmid using in-house designed gene specific primers. The frame and orientation of the inserted fliC gene was confirmed upon colony PCR, restriction enzyme analysis and sequencing. Sequence analysis of fliC revealed proper orientation of the gene and had 1,485 nucleotides. Following transformation of pET-fliC plasmid into Escherichia coli BL21 (DE3) cells, the gene was expressed after inducing with IPTG (Isopropylβ-D-1-thiogalactopyranoside). The polyHis-tag-fliC was ~70kDa as confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The identity/authenticity of the recombinant-fliC was confirmed by its specific reactivity with commercial anti-fliC MAb of S. Typhimurium. Further, the antigenic and functional properties of recombinant-fliC were determined espousing its ability to induce antigen specific antibodies in G pigs and increased m-RNA expression of certain pro-inflammatory mediators like TNF-α and GM-CSF in vitro.