Structure of the cyclic hexapeptide ligand PMX53, with amino acid sequence Ace-Phe-[Orn-Pro-dCha-Trp-Arg]. Panel A: two-dimensional Chemical structure PMX53. The N-terminal end is blocked by the group CH3-CO (Ace); Orn denotes ornithine and dCha d-cyclohexyl-alanine. The brackets denote cyclization via a covalent bond between the Orn side-chain and the Arg6 carbonyl group. Panel B: three-dimensional representation of the first conformer of the NMR ensemble of structures of PMX53. Atoms are colored according to element type. Panel C: three-dimensional representation of the ensemble of the NMR structures of PMX53. The color of residues transitions from blue to red between the N- and C- termini. Hydrogens are omitted for clarity.