[The in vitro refolding of β-barrel outer membrane protein of gram-negative bacteria--a review]

A cell of gram-negative bacteria is surrounded by two layers of membrane, the inner membrane and the outer membrane. Proteins are the major composition of outer membrane. Many outer membrane proteins carry a trans-membrane β-barrel structure that formed by multiple anti-parallel β-strands connected with hydrogen bonds. These proteins can act as porins, transporters, enzymes, receptors, virulence factors and structural proteins. Therefore, their correct folding and membrane integration are important for the survival of gram-negative bacteria. Most β-barrel outer membrane proteins could be easily expressed recombinantly and refolded in vitro under certain conditions. The in vitro folding processes could be monitored and investigated through many ways, which makes outer membrane proteins become a model system to study the effects of abiotic and biological factors on the folding of membrane proteins. In this article, the research progress on the in vitro refolding of outer membrane proteins are reviewed from the aspects of refolding methods, the factors that affect folding processes and experimental methods. Finally, the research prospects in this field are discussed.