6BBE image
Entry Detail
PDB ID:
6BBE
Title:
Structure of N-glycosylated porcine surfactant protein-D
Biological Source:
Source Organism:
Host Organism:
PDB Version:
Deposition Date:
2017-10-18
Release Date:
2018-05-23
Method Details:
Experimental Method:
Resolution:
1.90 Å
R-Value Free:
0.25
R-Value Work:
0.22
R-Value Observed:
0.22
Space Group:
P 63
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Pulmonary surfactant-associated protein D
Chain IDs:A
Chain Length:156
Number of Molecules:1
Biological Source:Sus scrofa
Primary Citation
Lectin-mediated binding and sialoglycans of porcine surfactant protein D synergistically neutralize influenza A virus.
J. Biol. Chem. 293 10646 10662 (2018)
PMID: 29769321 DOI: 10.1074/jbc.RA117.001430

Abstact

Innate 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 neck-CRD 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 nonlectin-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 Asn-303 of RpNCRD with complex-type, heterogeneously branched and predominantly α(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. The 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.

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