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Structure of N-glycosylated porcine surfactant protein-D complexed with glycerolStructure of N-glycosylated porcine surfactant protein-D complexed with glycerol
Structural highlights
FunctionSFTPD_PIG Contributes to the lung's defense against inhaled microorganisms, organic antigens and toxins. Interacts with compounds such as bacterial lipopolysaccharides, oligosaccharides and fatty acids and modulates leukocyte action in immune response. May participate in the extracellular reorganization or turnover of pulmonary surfactant. Binds strongly maltose residues and to a lesser extent other alpha-glucosyl moieties (By similarity). Publication Abstract from PubMedInnate immunity is critical in the early containment of influenza A virus (IAV) infection, and surfactant protein D (SP-D) plays a crucial role in the pulmonary defense against IAV. In pigs, which are important intermediate hosts during the generation of pandemic IAVs, SP-D uses its unique carbohydrate recognition domain (CRD) to interact with IAV. An N-linked CRD-glycosylation provides interactions with the sialic acid binding site of IAV, and a tripeptide loop at the lectin binding site facilitates enhanced interactions with IAV glycans. Here, to investigate both mechanisms of IAV neutralization in greater detail, we produced an N-glycosylated neckCRD fragment of porcine SP-D (RpNCRD) in HEK293 cells. X-ray crystallography disclosed that the N-glycan did not alter the CRD backbone structure including the lectin site conformation, but revealed a potential second non-lectin binding site for glycans. IAV hemagglutination inhibition, IAV aggregation and neutralization of IAV infection studies showed that RpNCRD, unlike the human analogue RhNCRD, exhibits potent neutralizing activity against pandemic A/Aichi/68 (H3N2), enabled by both porcine-specific structural features of its CRD. MS analysis revealed an N-glycan site-occupancy of >98% at Asn303 of RpNCRD with complex-type, heterogeneously branched and predominantly alpha(2,3) sialylated oligosaccharides. Glycan binding array data characterized both RpNCRD and RhNCRD as mannose-type lectins. RpNCRD also bound LewisY structures whereas RhNCRD bound polylactosamine-containing glycans. Presence of the N-glycan in the CRD increases the glycan binding specificity of RpNCRD. These insights increase our understanding of porcine-specific innate defense against pandemic IAV and may inform the design of recombinant SP-D-based antiviral drugs. Lectin-mediated binding and sialoglycans of porcine surfactant protein D synergistically neutralize influenza A virus.,van Eijk M, Rynkiewicz MJ, Khatri K, Leymarie N, Zaia J, White MR, Hartshorn KL, Cafarella TR, Van Die I, Hessing M, Seaton BA, Haagsman HP J Biol Chem. 2018 May 16. pii: RA117.001430. doi: 10.1074/jbc.RA117.001430. PMID:29769321[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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