S1P1 and LPA6 were first aligned to LPA1, which gave the lowest RMSD (S1P1:LPA1 = 0.986 Å, LPA6:LPA1 = 3.691 Å. Superimposed crystal structures of S1P1:LPA1, LPA1:LPA6, and S1P1:LPA6 are shown from the plane of the membrane (A), looking down from the N-termini and extracellular space (B), and looking up from the C-termini and intracellular space (C). S1P1 is shown in magenta, LPA1 in blue, and LPA6 in green. H, helix; N-term, N-terminus; TM, transmembrane helix