Integral membrane proteins (MPs) are categorized into two major groups:transmembrane (TM) α-helical bundles and β-barrels (Cymer et al.,2014).Both types of structures permit the backbones of their peptides to fulfill their hydrogen-bonding potential in a lipid-bilayer environment.The thermal stability of a typical β-barrel MP is usually much higher than that of a helical MP.Thus,β-barrel MPs are able to withstand near boiling-temperatures during purification (Han et al.,2016),compared with the typical melting temperatures of 50℃ or lower for α-helical TM proteins.