Figure 4.

Comparison of the two conformations of the ARFN peptide observed in the crystal structure. Shown is the first conformation of ARFN (ARFN-1) represented as sticks (green) with the HLA represented as a schematic (gray) with HLA side chains contacting the peptide shown as sticks (pink). The second conformation of the ARFN (ARFN-2) peptide is represented as sticks (blue) the HLA represented as a schematic (gray) with HLA side chains contacting the peptide shown as sticks (pink). A, conservation of contacts between the HLA and the ARFN-1 and ARFN-2 peptides at the P2-Arg position. B, conservation of contacts between the HLA and the ARFN-1 and ARFN-2 peptides at the PΩ-Val position. C, the ARFN-1 and ARFN-2 conformations differ in the orientation of their P7-Arg side chain. The P7-Arg of ARFN-1 forms a salt-bridge with Asp⁹, whereas the P7-Arg of ARFN-2 is shifted 5.8 Å and forms a salt-bridge with Asp¹¹⁴. D, plasticity of Trp⁹⁷ was observed between the HLA-C*06:02-ARTE and -ARFN structures. The ARTE, ARFN-1, and ARFN-2 peptides are shown as yellow, green, and blue sticks, respectively. The Trp⁹⁷ observed in the ARTE complex (orange sticks) is rotated 140° compared with the Trp⁹⁷ of the ARFN complex (pink sticks).