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Cover picture: Different approaches to determine hydrophobicity scales. The top two panels show (left) an experimental approach to determine the efficiency of membrane integration of α-helical segments, and (right) a "biological" hydrophobicity scale depicting the apparent free energy change ( ΔGaaapp) for placing each of the amino acids in the middle of a 19-residue-long α-helical segment (see article by von Heijne, 353–356; figure originally published in Hessa, T., H. Kim, K. Bihlmaier, C. Lundin, J. Boekel, H. Andersson, I. Nilsson, S.H. White, and G. von Heijne. 2005. Nature. 433:377–381). The bottom three panels show snapshots from molecular dynamics simulations to calculate the potential of mean force for moving amino acid side chain analogs from the aqueous phase into the bilayer (red and white sticks are water; DOPC phosphate and nitrogen groups are orange and blue spheres, the remainder is rendered as light gray lines). For the side chains: cyan, carbon; white, hydrogen; blue, nitrogen; and red, oxygen. (Left) Gln at 0.4 nm from the bilayer center is stabilized by a water defect; (center) Gln at 0.3 nm from the bilayer center has no associated water defect; (right) Arg at the bilayer center is stabilized by a water defect (see article by MacCallum et al., 371–377).
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