Figure 3

Interactions between amino acids of equal charge. Energy profiles (in kcal/mol) as a function of the interresidue distance d (in Å) for interactions: (a) between two negatively charged residues (Asp or Glu), and (b) between two positively charged residues (Lys or Arg), in globular proteins (dashed black line), extramembrane regions (blue line) and in transmembrane regions (red line). (c) Energy profiles of +/+ interactions in the transmembrane regions of α-helical proteins (orange) and β-barrel proteins (magenta). (d) Example of a cluster of four arginines separated by less then 4 Å inside the hydrophilic channel of the transmembrane region of KdgM porin from the Dickeya dadantii (PDB code 4FQE).