Figure 2

Distribution of amino acid residues involved into interhelical interactions in transmembrane regions of membrane proteins at heptad repeat positions abcdefg. Types of helical pairs are: AP-LH – antiparallel left-handed; AP-RH – antiparallel right-handed; P-LH – parallel left-handed; P-RH – parallel right-handed. The combined frequencies of interacting residues from helix-helix interfaces at a, d, e and g positions in the heptad repeat are: left-handed parallel helical pairs, 94.7%; left-handed antiparallel helical pairs, 92.4%; right-handed parallel helical pairs, 86.9%; and right-handed antiparallel helical pairs, 86.5%.