Stereo ribbon representation of LF, coloured by domain. The MAPKK-2 substrate is shown as a red ball-and-stick model, and the Zn2+ ion is labelled. The RMSD (Ca)between the cubic and monoclinic crystal forms is 1.18 Å. The principal differences lie in the position of the helical bundle of domain IV, which undergoes a rigid body shift of~2 Å relative to the b-sheet, and a smaller shift of the b-sheet of domain I. The third helicalelement of domain III is invisible in the monoclinic crystals, but can be seen in cubic crystals, albeit with high B-factors. It is possible that this mobile amphipathic helix has a role in the membrane-inserting properties of LF observed in vitro28.