Structural studies on HLA-G: implications for ligand and receptor binding.
Human leukocyte antigen-G (HLA-G) is a class Ib major histocompatibility complex (MHC) molecule that is specifically expressed in immune-privileged tissues. The overall structure of HLA-G resembles other class I MHC molecules, in which a heavy chain comprised of three domains is noncovalently associated with beta(2)microglobulin (beta(2)m). A nine-residue self-peptide is bound within a cleft formed by two alpha-helices and a beta-sheet floor. An extensive network of contacts is formed between the peptide and the binding cleft, leading to a constrained mode of binding reminiscent of that observed in HLA-E. The alpha3 domain of HLA-G, the putative binding site for leukocyte immunoglobulinlike receptor-1 (LIR-1) and -2, is structurally distinct from class Ia MHC molecules, providing a basis for the observed differences in affinity for these ligands. In addition, a disulfide-bonded dimer adopts an oblique conformation, providing the possibility of a 1:2 (HLA-G dimer:receptor) complex stoichiometry. The relative orientation of the HLA-G protomers in the dimer structure suggests that it is unlikely that dimerization is involved in killer immunoglobulinlike receptor 2DL4 (KIR2DL4) binding.
Clements
Craig S
CS
Protein Crystallography Unit, Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Victoria, Australia. craig.clements@med.monash.edu.au
Kjer-Nielsen
Lars
L
McCluskey
James
J
Rossjohn
Jamie
J
D019281:Dimerization; D006680:HLA Antigens / Q000737:chemistry* / Q000378:metabolism*; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D011485:Protein Binding / Q000502:physiology; D011971:Receptors, Immunologic / Q000378:metabolism*; D054346:Receptors, KIR2DL5
D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D008024:Ligands; D011971:Receptors, Immunologic; D054346:Receptors, KIR2DL5