The present disclosure relates to methods of expressing therapeutic proteins in photosynthetic organisms and the therapeutic proteins produced by the methods. The therapeutic proteins include high-mobility group box 1 (HMGB1) protein, fibronectin domain (10) (10FN3), fibronectin domain (14) (14FN3), interferon beta (IFNβ), proinsulin and vascular endothelial growth factor (VEGF). The photosynthetic organisms include prokaryotes such as cyanobacteria and eukaryotes such as alga and plants. Transformation of eukaryotes is preferably the plastid genome, more preferably the chloroplast genome.