Primary expression and identification of TLR4 extracellular fragment in Pichia pastoris

Objective To express and identify of Toll-like receptor 4 (TLR4) extracellular fragment in Pichia pastoris and to provide basis for the related researches. Methods The human TLR4 extracellular cDNA fragment was amplified by PCR and after confirming by DNA sequence analysis, was inserted into the Pichia pastoris expression vector pPIC9K containing AOX1 promoter and lead sequence of α factor gene to form a pPIC9K/TLR4 extracellular recombinant expression plasmid. The recombinant plasmid was transformed into GS115 and high copies transformants were screened with G418. After being identified by colony PCR, transformants were cultured in flasks and induced by 1% methanol. The expression products were analyzed by SDS-PAGE and were identified by Western blot analysis. Results The sequencing showed that TLR4 extracellular gene was identical to that in Genbank. The analysis for the recombinant plasmid DNA digested by enzyme demonstrated that the recombinant expression plasmids of pPIC9K/TLR4 extracellular were constructed successfully. After screening by G418, 200 high-copy-number of transformants were acquired. The special TLR4 extracellular gene segment was obtained by identification with colony PCR, which showed that TLR4 extracellular gene of 5 clones were inserted into Pichia pastoris. After methanol induction for 4 d, the expression proteins came up to 50.35% of total proteins in medium supernatant as shown by SDS-PAGE. Western blot analysis proved that the expression protein could bind to TLR4 monoclonal antibody specifically. Conclusion TLR4 extracellular protein is expressed and identified successfully by Pichia pastoris system, which can provide basis for the researches of further screening of high expression colony, protein purification, and functional research.