The
MHC class I molecule Mamu-B*17 has been associated with elite control of SIV
infection in rhesus macaques, akin to the protective effects described for
HLA-B*57 in HIV-infected individuals. In this study, we determined the crystal structures of Mamu-B*17 in complex with eight different
peptides corresponding to immunodominant SIV(mac)239-derived CD8(+)
T cell epitopes: HW8 (HLEVQGYW), GW10 (GSHLEVQGYW), MW9 (MHPAQTSQW), QW9 (QTSQWDDPW), FW9 (FQWMGYELW), MF8 (MRHVLEPF), IW9 (IRYPKTFGW), and IW11 (IRYPKTFGWLW). The structures reveal that not only P2, but also P1 and P3, can be used as N-terminal anchor residues by Mamu-B*17-restricted
peptides. Moreover, the N-terminal anchor residues exhibit a broad chemical specificity, encompassing basic (H and R), bulky polar aliphatic (Q), and small (T) residues. In contrast, Mamu-B*17 exhibits a very narrow preference for aromatic residues (W and F) at the C terminus, similar to that displayed by
HLA-B*57. Flexibility within the whole
peptide-binding groove contributes to the accommodation of these diverse
peptides, which adopt distinct conformations. Furthermore, the unusually large pocket D enables compensation from other
peptide residues if P3 is occupied by an
amino acid with a small side chain. In addition, residues located at likely TCR contact regions present highly flexible conformations, which may impact TCR repertoire profiles. These findings provide novel insights into the structural basis of diverse
peptide accommodation by Mamu-B*17 and highlight unique atomic features that might contribute to the protective effect of this MHC I molecule in SIV-infected rhesus macaques.