title: Ligand specificity of human surfactant protein D: expression of a mutant trimeric collectin that shows enhanced interactions with influenza A virus.
abstract: Surfactant protein D is a pattern recognition molecule that plays diverse roles in immune regulation and anti-microbial host defense. Its interactions with known ligands are calcium-dependent and involve binding to the trimeric, C-type carbohydrate recognition domain. Surfactant protein D preferentially binds to glucose and related sugars. However, CL-43, a bovine serum lectin, which evolved through duplication of the surfactant protein D gene in ruminants, prefers mannose and mannose-rich polysaccharides. Surfactant protein D is characterized by two relatively conserved motifs at the binding face, along the edges of the shallow carbohydrate-binding groove. For CL-43, sequence alignments demonstrate a basic insertion, Arg-Ala-Lys (RAK), immediately N-terminal to the first motif. We hypothesized that this insertion contributes to the differences in saccharide selectivity and host defense function and compared the activities of recombinant trimeric neck + carbohydrate recognition domains of human surfactant protein D (NCRD) with CL-43 (RCL-43-NCRD) and selected NCRD mutants. Insertion of the CL-43 RAK sequence or a control Ala-Ala-Ala sequence (AAA) into the corresponding position in NCRD increased the efficiency of binding to mannan and changed the inhibitory potencies of competing saccharides to more closely resemble those of CL-43. In addition, RAK resembled CL-43 in its greater capacity to inhibit the infectivity of influenza A virus and to increase uptake of influenza by neutrophils.
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. crouch@path.wustl.edu
authors.forename: Erika
authors.initials: E
authors.lastname: Crouch
authors.forename: Yizheng
authors.initials: Y
authors.lastname: Tu
authors.forename: David
authors.initials: D
authors.lastname: Briner
authors.forename: Barbara
authors.initials: B
authors.lastname: McDonald
authors.forename: Kelly
authors.initials: K
authors.lastname: Smith
authors.forename: Uffe
authors.initials: U
authors.lastname: Holmskov
authors.forename: Kevan
authors.initials: K
authors.lastname: Hartshorn
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000494:pharmacology; D002241:Carbohydrates / Q000737:chemistry; D002417:Cattle; D002845:Chromatography; D002850:Chromatography, Gel; D003432:Cross-Linking Reagents / Q000494:pharmacology; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004731:Endotoxins / Q000737:chemistry / Q000378:metabolism; D004765:Enteropeptidase / Q000378:metabolism; D005822:Genetic Vectors; D006801:Humans; D009980:Influenza A virus / Q000235:genetics* / Q000378:metabolism; D008024:Ligands; D008351:Mannans / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009504:Neutrophils / Q000378:metabolism; D017434:Protein Structure, Tertiary; D037663:Pulmonary Surfactant-Associated Protein D / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
chemical_list: D002241:Carbohydrates; D003432:Cross-Linking Reagents; D004731:Endotoxins; D008024:Ligands; D008351:Mannans; D037663:Pulmonary Surfactant-Associated Protein D; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D004765:Enteropeptidase; D002118:Calcium