Species differences in the carbohydrate binding preferences of surfactant protein D.
Interactions of surfactant protein D (SP-D) with micro-organisms and organic antigens involve binding to the trimeric neck plus carbohydrate recognition domain (neck+CRD). In these studies, we compared the ligand binding of homologous human, rat, and mouse trimeric neck+CRD fusion proteins, each with identical N-terminal tags remote from the ligand-binding surface. Although rat and mouse showed similar affinities for saccharide competitors, both differed markedly from the human protein. The human neck+CRD preferentially recognized N-acetyl-mannosamine, whereas the rat and mouse proteins showed greater affinity for myoinositol, maltose, and glucose. Although human neck+CRDs bound to maltosyl-agarose and fungal mannan, only rat and mouse neck+CRDs showed significant binding to maltosyl-Toyopearl beads, solid-phase maltosyl-albumin neo-glycoprotein, or the Phil82 strain of influenza A virus. Likewise, human SP-D dodecamers and trimeric subunits of full-length rat, but not full-length human SP-D trimers, bound to maltosyl-Toyopearl. Site-directed mutagenesis of the human neck+CRD demonstrated an important role of Asp324-Asp325 in the recognition of N-acetyl-mannosamine, and substitution of the corresponding murine sequence (Asn324-Asn325) conferred a capacity to interact with immobilized maltose. Thus, ligand recognition by human SP-D involves a complex interplay between saccharide presentation, the valency of trimeric subunits, and species-specific residues that flank the primary carbohydrate binding site.
Crouch
Erika C
EC
Dept. of Pathology and Immunology, Campus Box 8118, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA. crouch@path.wustl.edu
Smith
Kelly
K
McDonald
Barbara
B
Briner
David
D
Linders
Bruce
B
McDonald
Joseph
J
Holmskov
Uffe
U
Head
James
J
Hartshorn
Kevan
K
D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001667:Binding, Competitive; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D009980:Influenza A virus / Q000378:metabolism; D008320:Maltose / Q000378:metabolism*; D008351:Mannans / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011134:Polysaccharides / Q000378:metabolism; D011485:Protein Binding; D037663:Pulmonary Surfactant-Associated Protein D / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013045:Species Specificity; D013379:Substrate Specificity
D006023:Glycoproteins; D008351:Mannans; D011134:Polysaccharides; D037663:Pulmonary Surfactant-Associated Protein D; D011993:Recombinant Fusion Proteins; D001224:Aspartic Acid; C002076:pustulan; D008320:Maltose