The binding site of chicken hepatic lectin

Engineering galactose-binding activity into a C-type mannose-binding protein

Calcium-dependent or C-type carbohydrate-recognition domains are homologous protein modules found in a variety of animal lectins. Selective binding of sugars by these domains is essential for glycoprotein clearance, cell-cell adhesion and pathogen neutralization. Although various C-type carbohydrate-recognition domains share sequence identity ranging from 20 to 55%, their sugar-binding characteristics vary widely. The structure of a mannose-binding carbohydrate-recognition domain in complex with a saccharide ligand suggests that two glutamic acid-asparagine pairs are essential determinants of ligand binding by this domain. In C-type lectins that bind galactose with higher affinity than mannose, one of these pairs is replaced by glutamine-aspartic acid. Here we shift the sequence of the mannose-binding protein to correspond to that found in galactose-binding domains in order to test the importance of these residues in sugar-binding selectivity. This simple switch in the position of a single amide group alters the binding activity of the domain so that galactose becomes the preferred ligand.

Chick hepatic lectins: an electron microscopic study on isolated hepatocytes during development

We studied the carbohydrate recognition systems of hepatocytes isolated from 16-day-old embryos, 19-day-old embryos and chicks within 24 h of hatching. We localized and quantified at the ultrastructural level the binding sites for glycoproteins exposing terminal N-acetylglucosamine (GlcNAc), mannose and N-acetylgalactosamine (GalNAc) residues by means of protein-gold complexes. Binding sites specific for GlcNAc and mannose residues are present on hepatocytes from embryos and chicks. On the contrary GalNAc specific binding sites are exclusively observed on cells from 16-day-old embryos. The number and distribution of gold particles on hepatocyte cell surfaces depend on the binding sites and the age considered. We describe a modulation in the number of GlcNAc, and mannose specific receptors present on the cell surface between the embryonal stage and neonatal life.

Carbohydrate recognition systems in avian sinusoidal liver cells

We studied the carbohydrate recognition systems on liver sinusoidal cells of adult chicken and 20-day-old embryos. We localized and quantified the binding sites for glycoproteins exposing terminal N-acetylglucosamine (GlcNAc), mannose and galactose (Gal) residues. Sinusoidal liver cells from animals of both ages express on their cell surfaces binding sites for GlcNAc, mannose and galactose residues, while hepatocytes bind glycoproteins with GlcNAc residues. The gold particles distribution on Kupffer cells depend on the binding sites and the age considered. Binding sites for GlcNAc and Gal residues are generally present as clusters of gold granules, while mannose-specific binding sites are always as single gold granules. Ligand-gold complexes bound on endothelial cells are always present on the coated regions of the cell surface. The number of GlcNAc and Gal-specific receptors expressed on the cell surface of Kupffer cells undergoes modifications between embryonal and adult life.

Isolation and characterization of mannan-binding proteins from chicken liver

Two binding proteins which recognize and bind mannose and N-acetylglucosamine (mannan-binding proteins, MBP) have been isolated from chicken liver to near homogeneity mainly by affinity chromatography on a column of Sepharose 4B-mannan. The neutral binding protein (pI 7.0), which has a high glycine content, is an analog of mammalian liver MBP (F-I). F-I consists of a series of proteins composed of two subunits of 28,000 (A) and 32,000 (B) Da. The proteins have molecular weights ranging from 280,000 to 740,000 and subunit compositions ranging from 6A + 4B to 5A + 19B. With increasing molecular weight the specific activity of mannan binding increases gradually, accompanied by a slight change in specificity to a preference for mannose rather than N-acetylglucosamine. The acidic binding protein (pI 5.1) is a glycoprotein with a high glutamic acid content (F-II). The molecular weight of F-II was estimated to be 640,000, and it is composed of single subunits of 41,000 Da. The two MBPs isolated in this study are distinct from the liver lectin specific for N-acetylglucosamine-terminated glycoproteins isolated from the same source [T. Kawasaki and G. Ashwell (1977) J. Biol. Chem. 252, 6536-6543] in chemical properties and binding specificities.