Consequences of Hydrophobic Mismatch between Lipids and Melibiose Permease on Melibiose Transport

The structural and functional consequences of a mismatch between the hydrophobic thickness dP of a transmembrane protein and that dL of the supporting lipid bilayer were investigated using melibiose permease (MelB) from Escherichia coli reconstituted in a set of bis saturated and monounsaturated phosphatidylcholine species differing in acyl-chain length. Influence of MelB on the midpoint gel-to-liquid-phase transition temperature, Tm, of the saturated lipids was investigated through fluorescence polarization experiments, with 1,6-diphenyl-1,3,5-hexatriene as the probe, for varying protein/lipid molar ratio. Diagrams in temperature versus MelB concentration showed positive or negative shifts in Tm with the short-chain lipids DiC12:0-PC and DiC14:0-PC or the long-chain lipids DiC16:0-PC and DiC18:0-PC, respectively. Theoretical analysis of the data yielded a dL value of 3.0 ± 0.1 nm for the protein, similar to the 3.02 nm estimated from hydropathy profiles. Influence of the acyl chain length on the carrier ...