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Structure of the HCMV UL16-MICB complex elucidates select binding of a viral immunoevasin to diverse NKG2D ligands
Structural highlights
DiseaseMICB_HUMAN Genetic variations in MICA are a cause of susceptibility to rheumatoid arthritis (RA) [MIM:180300. It is a systemic inflammatory disease with autoimmune features and a complex genetic component. It primarily affects the joints and is characterized by inflammatory changes in the synovial membranes and articular structures, widespread fibrinoid degeneration of the collagen fibers in mesenchymal tissues, and by atrophy and rarefaction of bony structures. Note=The MICB*004 allele is associated with rheumatoid arthritis. Note=Genetic variation in MICB is associated with cytomegalovirus and herpes simplex virus I seropositivity and this may be associated with schizophrenia risk. FunctionMICB_HUMAN Seems to have no role in antigen presentation. Acts as a stress-induced self-antigen that is recognized by gamma delta T cells. Ligand for the KLRK1/NKG2D receptor. Binding to KLRK1 leads to cell lysis.[1] [2] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe activating immunoreceptor NKG2D promotes elimination of infected or malignant cells by cytotoxic lymphocytes through engagement of stress-induced MHC class I-related ligands. The human cytomegalovirus (HCMV)-encoded immunoevasin UL16 subverts NKG2D-mediated immune responses by retaining a select group of diverse NKG2D ligands inside the cell. We report here the crystal structure of UL16 in complex with the NKG2D ligand MICB at 1.8 A resolution, revealing the molecular basis for the promiscuous, but highly selective, binding of UL16 to unrelated NKG2D ligands. The immunoglobulin-like UL16 protein utilizes a three-stranded beta-sheet to engage the alpha-helical surface of the MHC class I-like MICB platform domain. Intriguingly, residues at the center of this beta-sheet mimic a central binding motif employed by the structurally unrelated C-type lectin-like NKG2D to facilitate engagement of diverse NKG2D ligands. Using surface plasmon resonance, we find that UL16 binds MICB, ULBP1, and ULBP2 with similar affinities that lie in the nanomolar range (12-66 nM). The ability of UL16 to bind its ligands depends critically on the presence of a glutamine (MICB) or closely related glutamate (ULBP1 and ULBP2) at position 169. An arginine residue at this position however, as found for example in MICA or ULBP3, would cause steric clashes with UL16 residues. The inability of UL16 to bind MICA and ULBP3 can therefore be attributed to single substitutions at key NKG2D ligand locations. This indicates that selective pressure exerted by viral immunoevasins such as UL16 contributed to the diversification of NKG2D ligands. Structure of the HCMV UL16-MICB complex elucidates select binding of a viral immunoevasin to diverse NKG2D ligands.,Muller S, Zocher G, Steinle A, Stehle T PLoS Pathog. 2010 Jan 15;6(1):e1000723. PMID:20090832[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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