Concerning Tryptophan and Protein–Bilayer Interactions

The perspectives on membrane protein insertion and protein–bilayer interactions (J. Gen. Physiol. 129:351–377) made important points concerning amino acid residue hydrophobicity, interfacial propensity, and membrane partitioning (MacCallum et al., 2007; von Heijne, 2007; White, 2007; Wolfenden, 2007). It is particularly striking that the relative ordering of the tendencies for particular amino acids to be inserted into a transmembrane helix from a translocon (Hessa et al., 2005) is highly correlated with the relative ordering of both (a) the experimental free energies for bare side chain (RH) transfer from cyclohexane to water (Wolfenden, 2007) and (b) the calculated free energies for side chain transfer from water to the center of a DOPC membrane (MacCallum et al., 2007). The relative octanol/water partitioning provides a good indication of interfacial propensity. Because water-saturated 1-octanol contains...