 The beta sandwich structure is held together through three hydrogen bonds between antiparallel strands 4 and 7 and one hydrogen bond between strands 1 and 5.The two helical stalks between subunits L and S intertwine with a single left-handed crossover into a coiled-coil at the top, near the globular domains forming a palm tree configuration.This region interacts with the two alpha helices of the second dimer in an opposite orientation to form a four-helix bundle and the dumbbell-shaped tetramer.