Use of modified BL21(DE3) Escherichia coli cells for high-level expressionof recombinant peanut allergens affected by poor codon usage

We previously cloned a panel of peanut allergens by phage display technolog y. Examination of the codons used in these sequences indicated that most of the cDNAs contain an excess of the least used codons in Escherichia coli, namely AGG/AGA, that correspond to a minor tRNA, the product of the dnaY ge ne. To achieve high-level expression of the peanut allergens, the cDNAs wer e subcloned into an expression vector of the pET series (Novagen) in order to produce (His),,tagged fusion proteins in conventional E. coli BL21(DE3) cells, The peanut allergens Ara h 1, Ara h 2, and Ara h 6 with an AGG/AGA c odon content of 8-10% were only marginally expressed, whereas the peanut pr ofilin Ara h 5, with an AGG/AGA codon content of only 0.8%, was efficiently expressed in these cells. Hence, by using modified BL21(DE3) E. coli cells , namely BL21-CodonPlus(DE3)-RIL cells (Stratagene) with extra copies of E. coli argU, ileY, and leuW tRNA genes, it was possible to attain high-level expression of the proteins affected by rare codon usage, IPTG-induced expr ession of several recombinant peanut allergens, such as Ara h 1, Ara h 2, a nd Ara h 6, was greatly increased in these special cells compared to the ex pression yield achieved by conventional E. coli hosts. The purification of the soluble and the insoluble fraction of Ara h 2 was performed by metal-af finity chromatography and yielded a total of about 30 mg (His),,tagged reco mbinant protein per liter of culture of transformed BL21(DE3)CodonPlus-RIL cells. This is over 100 times more than achieved by production of Ara h 2 i n conventional BL21(DE3) cells. (C) 2000 Academic Press.