(a) Structure of the UDP-N-acetylglucosamine acyltransferase (LPXA). This protein forms a Left-handed parallel β Helix (LβH). (b) Detail of one coil of the helix. Each coil is formed by three hexapeptides (shown in different colours). Note that hexapeptide positions i and i+4 point towards the inside of the prism whereas the other positions point outwards.