Volume 9, Issue 4, Pages 519-530 (October 1998) Structural Basis of CD8 Coreceptor Function Revealed by Crystallographic Analysis of a Murine CD8αα Ectodomain Fragment in Complex with H-2Kb  Petra S. Kern, Mai-kun Teng, Alex Smolyar, Jin-huan Liu, Ju Liu, Rebecca E. Hussey, Rebecca Spoerl, Hsiu-Ching Chang, Ellis L. Reinherz, Jia-huai Wang  Immunity  Volume 9, Issue 4, Pages 519-530 (October 1998) DOI: 10.1016/S1074-7613(00)80635-4

Figure 1 Overall View of the m-CD8αα/VSV8-H-2Kb Crystal Structure The CD8α1-A and the CD8α2-A subunits are shown as yellow and red ribbons, respectively. The H-2Kb α chain is blue-violet (α1, α2, and α3 domains labeled) and the mβ2M is green. The VSV8 peptide atoms and the N-acetylglucosamine residues are shown as sticks with atom type color coded. In this view, the antigen-presenting cell is at the bottom of the figure with the T cell approaching from the top. N- and C-termini of the CD8 subunits are labeled. All figures were created with SETOR (Evans 1993). Immunity 1998 9, 519-530DOI: (10.1016/S1074-7613(00)80635-4)

Figure 2 Comparison of Murine and Human CD8 and MHC Molecules (a) Sequence alignment of murine and human CD8α. mCD8α and hCD8α alignment in conjunction with the predicted alignment of mCD8β and domain 1 of hCD4 and the Bence Jones protein REI are shown. Except for CD8β, the alignment is based on β sheet framework structural superposition. The strand assignment and residue numbering is based on the mCD8αα/H-2Kb crystal structure. Selected residues characteristic for V type Ig domains are highlighted, including the cysteine and the β bulge residues and the mCD8α N terminus. (b) Sequence alignment of a segment of the H-2Kb and HLA-A2 α3 domains. Residues important for CD8 binding are highlighted, including the AB + CD loops. Residues making intermolecular hydrogen bonds are underlined. Immunity 1998 9, 519-530DOI: (10.1016/S1074-7613(00)80635-4)

Figure 3 Comparison between the Unligated VSV8/H-2Kb Molecule and the VSV8/H-2Kb Molecule Ligated with the CD8αα Homodimer Superposition of the unligated H-2Kb (red) and ligated H-2Kb (yellow) based on their α1 and α2 domains (residues 1–180) shows a hinge movement of the H-2Kb α3 domain (long arrow) and a movement of the mβ2M molecule around a pivot (short arrow). For clarity, the mCD8αα dimer and the VSV8 peptide have been omitted. Immunity 1998 9, 519-530DOI: (10.1016/S1074-7613(00)80635-4)

Figure 4 Comparison of mCD8αα/VSV8/H-2Kb and hCD8αα/HLA-A2 Complexes Superposition of the murine and the human complexes based on β sheet framework of 160 conserved CD8αα residues (mCD8αα-H-2Kb in red; hCD8αα-HLA-A2 in yellow) shows rocking of the H-2Kb molecule around the CD8 homodimer. Immunity 1998 9, 519-530DOI: (10.1016/S1074-7613(00)80635-4)

Figure 5 Detailed Interaction among mCD8αα and H-2Kb (a) mCD8αα/H-2Kb crystal structure. View is the same as in Figure 1 with the areas in squares detailed in (f), (c), and (e). Figure 5F is rotated relative to the view in (a). (b) Detailed view of the H-2Kb α3 CD loop. (c) H-2Kb α3 CD loop interaction with mCD8αα. The major binding interaction between the CD8 CDR3-like loop regions as well as CD8α2 β strand C with the α3 CD loop is shown. (d) Stabilization of the HLA-A2 α3 CD loop by the neighboring F strand. In contrast to the H-2Kb α3 CD loop (blue), the human counterpart (green) is pulled backward, away from the ligated hCD8αα molecule, by a hydrogen bonding network between the C and F strands. (e) Comparison of the MHC α3 AB loop interaction with the m- or hCD8α2 subunit. The H-2Kb AB loop (blue) is pointing toward the mCD8α2CDR2-like loop and is stabilized by two hydrogen bonds. The human counterpart assumes a different conformation, pointing away from the hCD8α2 (green). (f) Binding of CD8α1-A N-terminal residues to H-2Kb. The CD8α1-A N terminus (yellow) extends in between the H-2Kb α3 domain (blue) and the mβ2M (green) and is stabilized by five hydrogen bonds. The CD8α1-A Arg8 is hydrogen bonded to mβ2M and H-2Kb α3 residues. H-2Kb α2 domain residues Q115, D122, and E128 are not involved in binding of mCD8α1-A. Immunity 1998 9, 519-530DOI: (10.1016/S1074-7613(00)80635-4)

Figure 6 C-Terminal Sequence Alignment of Mammalian CD8β Chains, along with mCD8α The alignment is based on the conserved cysteine residues prior to the transmembrane domain of CD8α or β. All aligned CD8β sequences are shorter than the mCD8α sequence (h, human; r, rat; p, Pongo pygmaeus urangutan; m, mouse). Immunity 1998 9, 519-530DOI: (10.1016/S1074-7613(00)80635-4)