Intersubunit interactions in the MG491 tetramer.

<p>(a) The symmetric intersubunit interface, found only between subunits A (in green) and C (in orange), is mainly hydrophobic and involves the C-terminal end of helices α1. (b) The tight interface, found between neighbor subunits related by rotations of ~72° (tight dimers A-D or, analogously, C-B), is the largest intersubunits surface in the MG491 tetramer and is mainly electrostatic. (c) The loose interface, found between neighbor subunits related by rotations of ~108° (loose dimers D-C or, analogously, B-A), is composed of hydrophobic and hydrophilic patches evenly distributed. Red and blue surfaces represent electronegative and electropositive potentials, respectively. (d) Deviations from exact four-fold (blue dotted line) and two-fold (red and magenta dotted lines) molecular symmetries plotted against the residues number. The important asymmetric character of the tetramer is reflected in the large deviations for the four-fold symmetry, with an average value for Cα atoms of 7.33 Å.