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Publication Abstract from PubMed

Bovine conglutinin is an immune protein that is involved in host resistance to microbes and parasites and interacts with complement component iC3b, agglutinates erythrocytes, and neutralizes influenza A virus. Here, we determined the high-resolution (0.97-1.46 A) crystal structures with and without bound ligand of a recombinant fragment of conglutinin's C-terminal carbohydrate-recognition domain (CRD). The structures disclosed that the high-affinity ligand N-acetyl-D-glucosamine (GlcNAc) binds in the collectin CRD calcium site by interacting with the O3' and O4' hydroxyls alongside additional specific interactions of the N-acetyl group oxygen and nitrogen with Lys343 and Asp320, respectively. These residues, unique to conglutinin and differing both in sequence and location from those in other collectins, result in specific, high-affinity binding for GlcNAc. The binding pocket flanking residue Val339, unlike the equivalent Arg343 in the homologous human surfactant protein D, is sufficiently small to allow conglutinin Lys343 access to the bound ligand, whereas Asp320 lies in an extended loop proximal to the ligand-binding site and bounded at both ends by conserved residues that coordinate to both calcium and ligand. This loop becomes ordered on ligand binding. The electron density revealed both alpha and beta anomers of GlcNAc, consistent with the added alpha/betaGlcNAc mixture. Crystals soaked with alpha1-2 mannobiose, a putative component of iC3b, reported to bind to conglutinin, failed to reveal bound ligand, suggesting a requirement for presentation of mannobiose as part of an extended physiological ligand. These results reveal a highly specific GlcNAc-binding pocket in conglutinin and a novel collectin mode of carbohydrate recognition.

Atomic-resolution crystal structures of the immune protein conglutinin from cow reveal specific interactions of its binding site with N-acetylglucosamine.,Paterson JM, Shaw AJ, Burns I, Dodds AW, Prasad A, Reid KB, Greenhough TJ, Shrive AK J Biol Chem. 2019 Sep 27. pii: RA119.010271. doi: 10.1074/jbc.RA119.010271. PMID:31562242^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.