Molecular mechanisms of inhibition of influenza by surfactant protein D revealed by large-scale molecular dynamics simulation.
Surfactant protein D (SP-D), a mammalian C-type lectin, is the primary innate inhibitor of influenza A virus (IAV) in the lung. Interactions of SP-D with highly branched viral N-linked glycans on hemagglutinin (HA), an abundant IAV envelope protein and critical virulence factor, promote viral aggregation and neutralization through as yet unknown molecular mechanisms. Two truncated human SP-D forms, wild-type (WT) and double mutant D325A+R343V, representing neck and carbohydrate recognition domains are compared in this study. Whereas both WT and D325A+R343V bind to isolated glycosylated HA, WT does not inhibit IAV in neutralization assays; in contrast, D325A+R343V neutralization compares well with that of full-length native SP-D. To elucidate the mechanism for these biochemical observations, we have determined crystal structures of D325A+R343V in the presence and absence of a viral nonamannoside (Man9). On the basis of the D325A+R343V-Man9 structure and other crystallographic data, models of complexes between HA and WT or D325A+R343V were produced and subjected to molecular dynamics. Simulations reveal that whereas WT and D325A+R343V both block the sialic acid receptor site of HA, the D325A+R343V complex is more stable, with stronger binding caused by additional hydrogen bonds and hydrophobic interactions with HA residues. Furthermore, the blocking mechanism of HA differs for WT and D325A+R343V because of alternate glycan binding modes. The combined results suggest a mechanism through which the mode of SP-D-HA interaction could significantly influence viral aggregation and neutralization. These studies provide the first atomic-level molecular view of an innate host defense lectin inhibiting its viral glycoprotein target.
Beckman Institute and Department of Physics, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Boon Chong
BC
Goh
Michael J
MJ
Rynkiewicz
Tanya R
TR
Cafarella
Mitchell R
MR
White
Kevan L
KL
Hartshorn
Kimberly
K
Allen
Erika C
EC
Crouch
Oliviana
O
Calin
Peter H
PH
Seeberger
Klaus
K
Schulten
Barbara A
BA
Seaton
D000268:Adhesiveness; D019943:Amino Acid Substitution; D001665:Binding Sites; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D053122:Influenza A Virus, H3N2 Subtype / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism; D050296:Microbial Viability; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D037663:Pulmonary Surfactant-Associated Protein D / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D019267:Hemagglutinin Glycoproteins, Influenza Virus; D050505:Mutant Proteins; D010446:Peptide Fragments; D011134:Polysaccharides; D037663:Pulmonary Surfactant-Associated Protein D; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C483468:hemagglutinin, human influenza A virus; C092488:sialic acid receptor