Many engineered/designer proteins or single-chain antibodies are poorly expressed. Fusion with SUMO/SUMOstar enhances the stability, solubility, and yield of a protein. SUMO is one of the most conserved proteins in eukaryotes and have been shown to post-translationally modify a number of proteins in cells. SUMOylation plays an important role in various cellular process such as nuclear-cytosolic transport, transcriptional regulation, and protein stability. SUMO/SUMOstar-fusion leads to a dramatic enhancement of expression in E. coli, yeast, insect, and mammalian cells and promotes correct folding and hence biological activity. Additionally, this system simplifies and lowers the costs associated with protein expression and purification. Using this technology, a plethora of proteins have been shown to enhance their expression, stability, and yield.