Solubilization and refolding of inclusion bodies by detergents

Recombinant proteins play many important roles in development of biological reagents and biopharmaceuticals. Here, we will mainly review refolding of recombinant proteins when expressed in inclusion bodies, although strategies to enhance soluble expression are described as an alternative to refolding inclusion bodies. These strategies include, but not limited to, adding chemical chaperones in cell culture media, modifying cell lysis buffer and using solubility-enhacing fusion tags. Another solubility enhancement was to generate lipid complex for membrane proteins that form insoluble proteins without lipid. Among various solubilization and refolding technologies, those using denaturant, alkaline pH and pressure are also desribed, while we focus on solubilization and refolding using detergents, which are effective and cost-friendly. Sodium dodecylsulfate, lauroyl-glutamate, sarkosyl and cetyltrimethylammonium have been extensively used, as summarized in this review. Slow or step-wise removal of denaturants or ionic detergents used to solubilize appears to play a critical role in successful refolding by maintaining the solubility of proteins during refolding. In alkaline refolding, slow pH adjustment also helps maintain protein solubility. In pressure refolding, small amount of guanidine hydrochloride assisted refolding.