Enhanced expression of the human CD14 protein in tobacco using a 22-kDa alpha-zein signal peptide

The human CD14, a high affinity receptor for lipopolysaccharides (LPS), is involved in the innate immunity system and the inflammatory response. There is increasing interest in using recombinant approaches to produce purified CD14 protein for therapeutic uses. Plants provide ideal expression systems for the production of recombinant proteins, but the levels of expression of recombinant proteins produced in planta are still not high. To improve expression levels of CD14 the 22-kDa alpha-zein signal peptide (ZSP) from maize was fused to the human CD14 cDNA so that recombinant CD14 could stably accumulate in plant cells. The human CD14 gene and the modified human CD14 cDNA with the 22-kDa ZSP were respectively transformed into tobacco to produce transgenic plants. Western blot analysis confirmed human CD14 accumulation in the transgenic tobacco. The concentration of the recombinant protein in the tobacco leaves was measured by ELISA, and the results suggested that fusion with the 22-kDa alpha-ZSP effectively increased the accumulation of the recombinant protein (rCD14). The concentration of rCD14 in some of the transgenic lines was 19.54 μg g−1 tobacco leaf (fw), which was about 0.6 % of the total soluble protein. The rCD14 protein showed natural LPS-binding bioactivity by using U937 cells mensuration. Our results suggested that the maize 22-kDa alpha-zein signal peptide could be used to increase the accumulation of recombinant protein in tobacco leaves so that proteins can be produced in abundant biomass.