Forcing single-chain variable fragment production in tobacco seeds by fusion to elastin-like polypeptides

Single-chain variable fragments (scFvs), as well as other recombinant antibodies, have become powerful tools for therapy and analysis in both human and veterinary medicine. Transgenic plants have been developed as an efficient production system for these recombinant proteins, achieving high yields at moderate cost. Seeds are especially useful organs for molecular farming because of their high protein content and their ability to keep proteins functional during extended storage in ambient conditions. Several concepts have been applied to optimize protein accumulation in seeds, such as the use of specific promoters and transcription enhancers. In this paper, we present a new strategy to enhance substantially the expression of scFvs in transgenic tobacco seeds, based on C-terminal fusions to elastin-like polypeptides (ELPs). This strategy resulted in a 40-fold increase in scFv accumulation, with levels approaching 25% of total soluble protein. The fusion proteins show specific activities and affinities comparable with the properties of the corresponding scFvs. This strategy thus opens up new ways to improve greatly the production of recombinant antibodies in plant seeds.