Binding of core peptide FVLELEPEWTV (A, C, E) and extended ligand FVLELEPEWTVK (B, D, F) to HLA-A*02:01. Peptides are shown as sticks, while HLA-A*02:01 is shown as a molecular surface with electrostatic potential contoured from -30kT/E to +30kT/E (positive charge in blue, negative in red). Peptide FVLELEPEWTV in green, and FVLELEPEWTVK in yellow. 2FoFc electron density is shown as a blue mesh around the peptide (2 Å radius) FVLELEPEWTV (C) and FVLELEPEWTVK (D) and contoured at 1σ Details of peptide binding to the F’ pocket of MHC (E, F). MHCI residues that form H-bond interactions (blue dashed lines) with the peptide are labeled. MHC residues that are critical for the F’ pocket formation are shown with electron density with same settings as in C and D. (F) Note how Thr80 (T80) and Tyr84 (Y84) change position upon binding of extended ligand FVLELEPEWTVK. Those structural changes are not seen in PDB ID 2CLR (orange) when superimposed with UFP (16–26) and UFP (16–27).