Engineering Fibroblast Growth Factor-2 (FGF2) Production in Cyanobacteria.

The Fibroblast Growth Factor 2 (FGF2) is an important signaling protein that serves to activate a variety of biological processes in animal and human cells. The FGF2 comprises an uncommon β-barrel structure composed of β-pleated sheets and loops only. It functions as a multipurpose protein involved in cell growth, division, and repair. Accordingly, FGF2 is important in the biopharmaceutical/biomedical, as well as applied research fields. However, stable FGF2 expression and isolation in heterologous systems is hindered by the exclusively β-sheet structure of this protein. Synechocystis sp. PCC 6803 is a freshwater, single-celled cyanobacterium serving as a model organism in photosynthesis and synthetic biology research. To stabilize and enhance accumulation of FGF2 in Synechocystis, the codon-optimized FGF2 gene was installed as a fusion construct with the highly expressed CpcB β-subunit of phycocyanin. This enabled stable recombinant FGF2 accumulation in Synechocystis, overcoming the difficulty due to the occurrence of β-sheets only in the structure of this protein. Furthermore, the recombinant phycocyanin-FGF2 fusion protein (Phyco*FGF2) exhibited both phycocyanin and FGF2 bioactivity. The work supports the concept that cyanobacterial cells will tolerate difficult-to-express heterologous recombinant proteins when fused to phycocyanin, as the latter is needed for photosynthesis and cellular growth, thus enabling a stoichiometric accumulation, in this case between phycocyanin and the FGF2 protein.