Structures of CU202, CU201, SPD2, SPD-D, CP126, and CP127. Hyp, trans-4-hydroxyproline; Igl, α-(2-indanyl) glycine; Oic, octahydroindole-2-carboxylic acid; SUIM, suberimidate linker; BMH, bismaleimidohexane; FDF, 4-fluoro-d-phenylalanine; FDW, 5-fluoro-d-tryptophan.