 They are made up of two, antiparallel beta sheets that face each other in a beta sandwich-like structure (i.e., a "flattened" beta barrel) and are separated by two alpha helices on one side.The N-terminus begins with one beta sheet composed of strands 1, 2, 3, and 4, followed by a helix-turn-helix motif of the two alpha helices, αA and αB, which continues into strands 5, 6, 7, and ending with one alpha-helical stalk at the C-terminus.αA and αB are perpendicular to one another, and because one end of αB is partially inserted between the two beta sheets, it causes them to flare out away from each other.