Published ahead of print on March 2, 2006, doi:10.1165/rcmb.2005-0462OC
© 2006 American Thoracic Society DOI: 10.1165/rcmb.2005-0462OC Species Differences in the Carbohydrate Binding Preferences of Surfactant Protein DDepartment of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri; Medical Biology Center, University of Southern Denmark, Odense, Denmark; and Department of Physiology and Department of Medicine, Boston University School of Medicine, Boston, Massachusetts Correspondence and requests for reprints should be addressed to Erika C. Crouch, M.D., Ph.D., Dept. of Pathology and Immunology, Campus Box 8118, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110. E-mail: crouch{at}path.wustl.edu 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.
Key Words: carbohydrate recognition domain • collectin • lectin • SP-D This article has been cited by other articles:
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