High yield recombinant silk-like protein production in transgenic plants through protein targeting.

DP1B is a synthetic analogue of spider dragline silk protein. It can be spun to form silk fiber. Previously, it had been expressed in transgenic plants, showing the general feasibility of the plant-based DP1B production. However, success of such a plant-based platform requires a great increase of DP1B productivity in plant cells to reduce production cost. This report describes a protein targeting approach to accumulate DP1B in apoplast, ER lumen, and vacuole in Arabidopsis cells, by utilizing appropriate combinations of sporamin-targeting determinant peptides and ER retention peptide. The approach has dramatically enhanced DP1B accumulation, resulting in high production yield. The accumulation can be as high as 8.5 and 6.7% total soluble protein in leaf tissue by targeting to apoplast and ER lumen, respectively, or as high as 18 and 8.2% total soluble protein in seeds by targeting to ER lumen and vacuole, respectively. However, the vacuole targeting in leaves and the apoplast targeting in seeds have failed to accumulate full length DP1B molecules or any DP1B at all, respectively, suggesting that they may not be suitable for applications in leaf tissues and seeds. Data in this study recommend a combination of seed-specific expression and ER-targeting as one of the best strategies for yield enhancement of plant-based DP1B production.