Killer cell immunoglobulin-like receptor 3DL1 polymorphism defines distinct hierarchies of HLA class I recognition

Natural killer (NK) cells play a key role in immunity, but how HLA class I (HLA-I) and killer cell immunoglobulin-like receptor 3DL1 (KIR3DL1) polymorphism impacts disease outcome remains unclear. KIR3DL1 (*001/*005/*015) tetramers were screened for reactivity against a panel of HLA-I molecules. This revealed different and distinct hierarchies of specificity for each KIR3DL1 allotype, with KIR3DL1*005 recognizing the widest array of HLA-I ligands. These differences were further reflected in functional studies using NK clones expressing these specific KIR3DL1 allotypes. Unexpectedly, the Ile/Thr80 dimorphism in the Bw4-motif did not categorically define strong/weak KIR3DL1 recognition. Although the KIR3DL1*001, *005, and *015 polymorphisms are remote from the KIR3DL1-HLA-I interface, the structures of these three KIR3DL1-HLA-I complexes showed that the broader HLA-I specificity of KIR3DL1*005 correlated with an altered KIR3DL1*005 interdomain positioning and increased mobility within its ligand-binding site. Collectively, we provide a generic framework for understanding the impact of KIR3DL1 polymorphism on the recognition of HLA-I allomorphs

MHC-I peptides get out of the groove and enable a novel mechanism of HIV-1 escape

Major histocompatibility complex class I (MHC-I) molecules play a crucial role in immunity by capturing peptides for presentation to T cells and natural killer (NK) cells. The peptide termini are tethered within the MHC-I antigen-binding groove, but it is unknown whether other presentation modes occur. Here we show that 20% of the HLA-B*57:01 peptide repertoire comprises N-terminally extended sets characterized by a common motif at position 1 (P1) to P2. Structures of HLA-B*57:01 presenting N-terminally extended peptides, including the immunodominant HIV-1 Gag epitope TW10 (TSTLQEQIGW), showed that the N terminus protrudes from the peptide-binding groove. The common escape mutant TSNLQEQIGW bound HLA-B*57:01 canonically, adopting a dramatically different conformation than the TW10 peptide. This affected recognition by killer cell immunoglobulin-like receptor (KIR) 3DL1 expressed on NK cells. We thus define a previously uncharacterized feature of the human leukocyte antigen class I (HLA-I) immunopeptidome that has implications for viral immune escape. We further suggest that recognition of the HLA-B*57:01-TW10 epitope is governed by a 'molecular tension' between the adaptive and innate immune systems

A Novel Serpin Regulatory Mechanism

exterior, yard gate, July-Sept. 198

The structure of the atypical killer cell immunoglobulin-like receptor, KIR2DL4

The engagement of Natural Killer (NK) cell Immunoglobulin-Like Receptors (KIRs) with their target ligands, Human Leukocyte Antigen (HLA) molecules, is a critical component of innate immunity. Structurally, KIRs typically have either two (D1-D2) or three (D0-D1-D2) extracellular immunoglobulin domains, with the D1 and D2 domain recognizing the α1 and α2 helices of HLA respectively, while the D0 domain of the KIR3DLs binds a loop region flanking the α1 helix of the HLA molecule. KIR2DL4 is distinct from other KIRs (except KIR2DL5) in that it does not contain a D1 domain and instead has a D0-D2 arrangement. Functionally, KIR2DL4 is also atypical in that, unlike all other KIRs, KIR2DL4 has both activating and inhibitory signaling domains. Here, we determined the 2.8 Å crystal structure of the extracellular domains of KIR2DL4. Structurally, KIR2DL4 is reminiscent of other KIR2DL receptors, with the D0 and D2 adopting the C2-type immunoglobulin fold arranged with an acute elbow angle. However, KIR2DL4 self-associated via the D0 domain in a concentration-dependent manner and was observed as a tetramer in the crystal lattice, by size-exclusion chromatography, dynamic light scattering, analytical ultra-centrifugation and small-angle X-ray scattering experiments. The assignment of residues in the D0 domain to forming the KIR2DL4 tetramer precludes an interaction with HLA akin to that observed for KIR3DL1. Accordingly, no interaction was observed to HLA by direct binding studies. Our data suggest that the unique functional properties of KIR2DL4 may be mediated by self-association of the receptor

The Interaction of KIR3DL1*001 with HLA Class I Molecules Is Dependent upon Molecular Microarchitecture within the Bw4 Epitope

The killer cell Ig-like receptor 3DL1 (KIR3DL1) inhibits activation of NK cells upon interaction with HLA class I molecules such as HLA-B*57:01, which contains the Bw4 epitope spanning residues 77-83 (e.g., NLRIALR), and not with HLA allomorphs that possess the Bw6 motif (e.g., HLA-B*08:01), which differ at residues 77, 80, 81, 82, and 83. Although Bw4 residues Ile(80) and Arg(83) directly interact with KIR3DL1*001, their precise role in determining KIR3DL1-HLA-Bw4 specificity remains unclear. Recognition of HLA-B*57:01 by either KIR3DL1(+) NK cells or the NK cell line YTS transfected with KIR3DL1*001 was impaired by mutation of residues 80 and 83 of HLA-B*57:01 to the corresponding amino acids within the Bw6 motif. Conversely, the simultaneous introduction of three Bw4 residues at positions 80, 82, and 83 into HLA-B*08:01 conferred an interaction with KIR3DL1*001. Structural analysis of HLA-B*57:01, HLA-B*08:01, and mutants of each bearing substitutions at positions 80 and 83 revealed that Ile(80) and Arg(83) within the Bw4 motif constrain the conformation of Glu(76), primarily through a salt bridge between Arg(83) and Glu(76). This salt bridge was absent in HLA-Bw6 molecules as well as position 83 mutants of HLA-B*57:01. Mutation of the Bw4 residue Ile(80) also disrupted this salt bridge, providing further insight into the role that position 80 plays in mediating KIR3DL1 recognition. Thus, the strict conformation of HLA-Bw4 allotypes, held in place by the Glu(76)-Arg(83) interaction, facilitates KIR3DL1 binding, whereas Bw6 allotypes present a platform on the α1 helix that is less permissive for KIR3DL1 binding

The Structure of the Atypical Killer Cell Immunoglobulin-like Receptor, KIR2DL4

The engagement of Natural Killer (NK) cell Immunoglobulin-Like Receptors (KIRs) with their target ligands, Human Leukocyte Antigen (HLA) molecules, is a critical component of innate immunity. Structurally, KIRs typically have either two (D1-D2) or three (D0-D1-D2) extracellular immunoglobulin domains, with the D1 and D2 domain recognizing the α1 and α2 helices of HLA respectively, while the D0 domain of the KIR3DLs binds a loop region flanking the α1 helix of the HLA molecule. KIR2DL4 is distinct from other KIRs (except KIR2DL5) in that it does not contain a D1 domain and instead has a D0-D2 arrangement. Functionally, KIR2DL4 is also atypical in that, unlike all other KIRs, KIR2DL4 has both activating and inhibitory signaling domains. Here, we determined the 2.8 Å crystal structure of the extracellular domains of KIR2DL4. Structurally, KIR2DL4 is reminiscent of other KIR2DL receptors, with the D0 and D2 adopting the C2-type immunoglobulin fold arranged with an acute elbow angle. However, KIR2DL4 self-associated via the D0 domain in a concentration-dependent manner and was observed as a tetramer in the crystal lattice, by size-exclusion chromatography, dynamic light scattering, analytical ultra-centrifugation and small-angle X-ray scattering experiments. The assignment of residues in the D0 domain to forming the KIR2DL4 tetramer precludes an interaction with HLA akin to that observed for KIR3DL1. Accordingly, no interaction was observed to HLA by direct binding studies. Our data suggest that the unique functional properties of KIR2DL4 may be mediated by self-association of the receptor