Figure 1.

LPC presentation by human CD1d. (A) The change in intrinsic tryptophan fluorescence of CD1d as a function of titrated amounts of LPC. The increase of tryptophan fluorescence with increasing amounts of LPC was expressed as a ratio (F−F_o)/F_o, the change in fluorescence divided by the control fluorescence in the absence of added LPC. The data were fit to a one-site binding model to determine the apparent K_D of this interaction. (B) Semitransparent surface and ribbon diagram of the structure of human CD1d (cyan) presenting LPC (yellow). Two spacer lipids identified in the electron density, C11 and C6 and the location of the A’ and F’ pockets are also shown. (C) Electron density of lysophosphatidylcholine (LPC) and the N-linked glycosylation in the CD1d–LPC structure. CD1d is shown from above as a ribbon diagram in cyan and 2F_o−F_c electron density maps contoured at 1α around the LPC ligand, C11 and C6 is coloured in pink, and around the glycosylation at N20 is coloured in green. (D) Phosphorylcholine headgroup coordination of LPC by CD1d. Main chain of CD1d is shown as cyan ribbon, whereas side chains mediating the coordination are shown as stick. Atoms are coloured as follows: blue=nitrogen, red=oxygen, orange=phosphorus and yellow=carbon. Two hydrogen bonded water molecules are shown as spheres coloured in marine. The positive and negative charges of the Arg79 and the phosphate moiety are shown as ‘+’ and ‘−’, respectively. Hydrogen bonds are shown as dashed yellow lines: highly likely H-bonds (>3.3 Å) are shown with heavy dashed lines, probable H-bonds (4 Å> but >3.3 Å) are shown as light dashed lines.