title: Crystal structure of myeloid cell activating receptor leukocyte Ig-like receptor A2 (LILRA2/ILT1/LIR-7) domain swapped dimer: molecular basis for its non-binding to MHC complexes.
abstract: The leukocyte Ig-like receptor (LILR/ILT/LIR) family comprises 13 members that are either activating or inhibitory receptors, regulating a broad range of cells in the immune responses. LILRB1 (ILT2), LILRB2 (ILT4) and LILRA1 (LIR6) can recognize MHC (major histocompatibility complex) class I or class I-like molecules, and LILRB1/HLA-A2, LILRB1/UL18 and LILRB2/HLA-G complex (extracellular domains D1D2) structures have been solved recently. The details of binding to MHC have been described. Despite high levels of sequence similarity among LILRA1, LILRA2 (ILT1), LILRA3 (ILT6) and LILRB1/B2, all earlier experiments showed that LILRA2 does not bind to MHC, but the reason is unknown. Here, we report the LILRA2 extracellular D1D2 domain crystal structure at 2.6 A resolution, which reveals structural shifts of the corresponding MHC-binding amino acid residues in comparison with LILR B1/B2, explaining its non-binding to MHC molecules. We identify some key residues with great influence on the local structure, which exist only in the MHC-binding receptors. Moreover, we show that LILRA2 forms a domain-swapped dimer. Further work with these key swapping residues yields a monomeric form, confirming that the domain-swapping is primarily amino acid sequence-specific. The structure described here supports the dimer conformation in solution observed earlier, and implies a stress-induced regulation by dimerization, consistent with its function as a heat shock promoter.
authors.affiliation: Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Chen
authors.forename: Feng
authors.initials: F
authors.lastname: Gao
authors.forename: Fuliang
authors.initials: F
authors.lastname: Chu
authors.forename: Hao
authors.initials: H
authors.lastname: Peng
authors.forename: Lili
authors.initials: L
authors.lastname: Zong
authors.forename: Yiwei
authors.initials: Y
authors.lastname: Liu
authors.forename: Po
authors.initials: P
authors.lastname: Tien
authors.forename: George F
authors.initials: GF
authors.lastname: Gao
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D006649:Histocompatibility Antigens / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D006649:Histocompatibility Antigens; C105298:LILRA2 protein, human; D011971:Receptors, Immunologic