Crystal structures of HLA B*3508^CPS and HLA B*3508^FPT. Panels A and C showing the electron density 2mfo-Dfc at 1σ of the FPT (orange stick) or CPS (purple stick) epitope bound to HLA B*3508. Panel B represents the structures of the featureless FPT peptide (orange) superposed with the one of the bludged CPS epitope (purple), which made one helix turn in its c-terminus. Panels D and E show surface view of the CPS and FPT epitopes bound to the HLA B*3508 molecule. The solvent-exposed surface of the peptide, which is accessible to the TCR, is represented by the green surface. The FPT epitope (panel E) has a smaller solvent-exposed surface than the CPS epitope (panel D).