PILRα and PILRβ have a siglec fold and provide the basis of binding to sialic acid.
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 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 PILRα form the SA binding site equivalent to those in siglecs but are arranged in a unique linear mode. PILRβ differs from PILRα in one of these three residues (L108), explaining its inability to engage gB. Mutation of L108 to tryptophan in PILRβ restored the gB-binding capacity. We further solved the structure of this PILRβ 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.
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;University of Chinese Academy of Sciences, Beijing 100049, China;
Qiong
Q
Lu
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;
Guangwen
G
Lu
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;
Jianxun
J
Qi
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;University of Chinese Academy of Sciences, Beijing 100049, China;
Han
H
Wang
Research Network of Immunity and Health, Beijing Institutes of Life Science, Chinese Academy of Sciences, Beijing 100101, China;
Yifang
Y
Xuan
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;
Qihui
Q
Wang
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;
Yan
Y
Li
Laboratory of Protein Engineering and Vaccines, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China;
Yanfang
Y
Zhang
Institutes of Biology and Medical Sciences, Soochow University, Suzhou 215123, China; and.
Chunfu
C
Zheng
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;
Zheng
Z
Fan
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;
Jinghua
J
Yan
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China;University of Chinese Academy of Sciences, Beijing 100049, China;Research Network of Immunity and Health, Beijing Institutes of Life Science, Chinese Academy of Sciences, Beijing 100101, China;Laboratory of Protein Engineering and Vaccines, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China;Office of Director-General, Chinese Center for Disease Control and Prevention, Beijing 102206, China gaof@im.ac.cn.
George F
GF
Gao
D000818:Animals; D016466:CHO Cells; D003412:Cricetulus; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D019158:N-Acetylneuraminic Acid / Q000378:metabolism*; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D063265:Sialic Acid Binding Immunoglobulin-like Lectins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000378:metabolism
D004220:Disulfides; D008562:Membrane Glycoproteins; C412263:PILRA protein, human; C404960:PILRB protein, human; D011971:Receptors, Immunologic; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; D014759:Viral Envelope Proteins; C040495:glycoprotein B, Simplexvirus; D019158:N-Acetylneuraminic Acid