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PILR? and PILR? have a siglec fold and provide the basis of binding to sialic acid.

ABSTRACT: Paired immunoglobulin-like type 2 receptor ? (PILR?) and ? (PILR?) belong to the PILR family and are related to innate immune regulation in various species. Despite their high sequence identity, PILR? and PILR? are shown to have variant sialic acid (SA) binding avidities. To explore the molecular basis of this interaction, we solved the crystal structures of PILR? and PILR? at resolutions of 1.6 Å and 2.2 Å, respectively. Both molecules adopt a typical siglec fold but use a hydrophobic bond to substitute the siglec-specific disulfide linkage for protein stabilization. We further used HSV-1 glycoprotein B (gB) as a representative molecule to study the PILR-SA interaction. Deploying site-directed mutagenesis, we demonstrated that three residues (Y2, R95, and W108) presented on the surface of PILR? form the SA binding site equivalent to those in siglecs but are arranged in a unique linear mode. PILR? differs from PILR? in one of these three residues (L108), explaining its inability to engage gB. Mutation of L108 to tryptophan in PILR? restored the gB-binding capacity. We further solved the structure of this PILR? mutant complexed with SA, which reveals the atomic details mediating PILR/SA recognition. In comparison with the free PILR structures, amino acid Y2 oriented variantly in the complex structure, thereby disrupting the linear arrangement of PILR residues Y2, R95, and W108. In conclusion, our study provides significant implications for the PILR-SA interaction and paves the way for understanding PILR-related ligand binding.

SUBMITTER: Lu Q

PROVIDER: S-EPMC4050567 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature

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PILRα and PILRβ have a siglec fold and provide the basis of binding to sialic acid.

Lu Qiong Q Lu Guangwen G Qi Jianxun J Wang Han H Xuan Yifang Y Wang Qihui Q Li Yan Y Zhang Yanfang Y Zheng Chunfu C Fan Zheng Z Yan Jinghua J Gao George F GF

Proceedings of the National Academy of Sciences of the United States of America 20140519 22

Paired immunoglobulin-like type 2 receptor α (PILRα) and β (PILRβ) belong to the PILR family and are related to innate immune regulation in various species. Despite their high sequence identity, PILRα and PILRβ are shown to have variant sialic acid (SA) binding avidities. To explore the molecular basis of this interaction, we solved the crystal structures of PILRα and PILRβ at resolutions of 1.6 Å and 2.2 Å, respectively. Both molecules adopt a typical siglec fold but use a hydrophobic bond to s ...[more]

PMID: 24843130

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Project description:BACKGROUND:Siglec-8 is a CD33 subfamily cell-surface receptor selectively expressed on human eosinophils. After cytokine priming, Siglec-8 mAb or glycan ligand binding causes eosinophil apoptosis associated with reactive oxygen species (ROS) production. Most CD33-related Siglecs function as inhibitory receptors, but the ability of Siglec-8 to stimulate eosinophil ROS production and apoptosis suggests that Siglec-8 might instead function as an activating receptor. OBJECTIVE:We sought to determine the role of IL-5 priming and identify the signaling molecules involved in Siglec-8 function for human eosinophils. METHODS:We used an mAb and/or a multimeric synthetic sulfated sialoglycan ligand recognizing Siglec-8 in combination with integrin blocking antibodies, pharmacologic inhibitors, phosphoproteomics, and Western blot analysis to define the necessity of various proteins involved in Siglec-8 function for human eosinophils. RESULTS:Cytokine priming was required to elicit the unanticipated finding that Siglec-8 engagement promotes rapid ?2-integrin-dependent eosinophil adhesion. Also novel was the finding that this adhesion was necessary for subsequent ROS production and apoptosis. Siglec-8-mediated ROS was generated through reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation because pretreatment of eosinophils with catalase (an extracellular superoxide scavenger) or NSC 23766 (a Rac GTPase inhibitor) completely inhibited Siglec-8-mediated eosinophil apoptosis. Finally, engagement of Siglec-8 on IL-5-primed eosinophils resulted in increased phosphorylation of Akt, p38, and c-Jun N-terminal kinase 1 that was also ?2-integrin dependent; pharmacologic inhibition of these kinases completely prevented Siglec-8-mediated eosinophil apoptosis. CONCLUSIONS:These data demonstrate that Siglec-8 functions uniquely as an activating receptor on IL-5-primed eosinophils through a novel pathway involving regulation of ?2-integrin-dependent adhesion, NADPH oxidase, and a subset of protein kinases.

Dataset Information

PILR? and PILR? have a siglec fold and provide the basis of binding to sialic acid.

Publications

PILRα and PILRβ have a siglec fold and provide the basis of binding to sialic acid.

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