Fig. 2.

Inside and outside forces for coiled coil stabilization. (A) Inside forces are classical "knobs into holes" formations of aliphatic side chains oriented inside the coiled-coil channel. In addition to a and h positioned "knobs into holes" the right-handed coiled coil from Staphylothermus marinus reveals a so far unknown inter-helical hydrophobic core composed of residues in d and e positions (de-layer). (B) In the case of the pentameric COMPcc (PBD-code 1VDF), a ring of five Gln⁵⁴ residues in position d is arranged to form an inter-helical network of ionic interactions (red dotted lines) and contributes to the binding (green dotted lines) of a chloride ion (highlighted in yellow). (C) Molecular surface model of the tetrameric RHCC structure. Only the front two helices of the RHCC tetramer are shown. Hydrophobic residues are depicted in grey, whereas positively- and negatively-charged residues, which form the major i-i′ + 2 (inter-helical) and i−i + 3 (intra-helical) salt bridges are depicted in blue and red, respectively.