Production of Biologically Active Human Thioredoxin 1 Protein in Lettuce Chloroplasts

Abstract

The production of human therapeutic proteins in plants provides opportunities for low-cost production, and minimizes the risk of contamination from potential human pathogens. Chloroplast genetic engineering is a particularly promising strategy, because plant chloroplasts can produce large amounts of foreign target proteins. Human thioredoxin 1 (hTrx1) is an antioxidant protein, and can suppress various diseases in mice. Therefore, hTrx1 is a prospective candidate as a human therapeutic protein.
We created transplastomic lettuce expressing hTrx1 gene under the control of the tobacco psbA promoter. The hTrx1 protein accumulated to approximately 3% of total soluble protein in mature leaves. The hTrx1 protein purified from lettuce leaves was functionally active, and reduced insulin disulfides. The purified protein protected MIN6 cells from damage by hydrogen peroxide, as reported previously for a recombinant hTrx1 form Escherichia coli. This is the first report for expression of the biologically active hTrx1 protein in plant chloroplasts. Considering that this expression host is an edible crop plant, this transplastomic lettuce may be suitable for oral delivery of hTrx1.