Strategies for Alleviating in vitro Low Protein Solubility in Applied Biotechnology and Microbiology

From research to application, high protein solubility is usually a desired property yet sometimes difficult to achieve. The in vitro low solubility of the fully folded proteins is relevant to applied microbiological studies, biochemical studies, biopharmaceutical studies, high-resolution structural studies, and applications demanding high protein concentration. This insufficient protein solubility depends largely on the surface property of the protein molecule. To alleviate this problem, approaches emphasized on the improvement of water-binding ability or prevention of protein aggregation were employed including the use of chemical additives, fusion with solubility enhancement tags, and molecular engineering of the surface amino acid residues. With the availability of the three-dimensional structure of the target proteins, the effect of different surface amino acid residues on protein solubility could be systematically investigated. With the applications of advanced bioinformatics tools and guided by protein three-dimensional structure, solubility-improving mutagenesis can be designed and executed with a high chance of success. Integrating rational molecular engineering with other available approaches will be the effective strategy for alleviating in vitro low solubility of important proteins in the future.