Figure 6

Cation-π interactions between Lys or Arg and Phe, Tyr or Trp (a) Energy profile (in kcal/mol) as a function of the interresidue distance d (in Å) in globular proteins (dashed black), extramembrane regions (blue) and transmembrane regions (red). (b) Energy profile in α-helical (orange) and β-barrel (magenta) transmembrane regions. (c,d) Distribution of the θ angle between the aromatic and guanidinium planes, for Arg-involving cation-π interactions. 0° corresponds to stacked and 90° to parallel conformations. (c) Distributions from extramembrane regions are in blue and those from transmembrane regions in red. (d) Distributions from α-helical (orange) and β-barrel (magenta) transmembrane proteins.