title: Biochemical and structural characterization of the novel sialic acid-binding site of Escherichia coli heat-labile enterotoxin LT-IIb.
abstract: The structurally related AB5-type heat-labile enterotoxins of Escherichia coli and Vibrio cholerae are classified into two major types. The type I group includes cholera toxin (CT) and E. coli LT-I, whereas the type II subfamily comprises LT-IIa, LT-IIb and LT-IIc. The carbohydrate-binding specificities of LT-IIa, LT-IIb and LT-IIc are distinctive from those of cholera toxin and E. coli LT-I. Whereas CT and LT-I bind primarily to the GM1 ganglioside, LT-IIa binds to gangliosides GD1a, GD1b and GM1, LT-IIb binds to the GD1a and GT1b gangliosides, and LT-IIc binds to GM1, GM2, GM3 and GD1a. These previous studies of the binding properties of type II B-subunits have been focused on ganglio core chain gangliosides. To further define the carbohydrate binding specificity of LT-IIb B-subunits, we have investigated its binding to a collection of gangliosides and non-acid glycosphingolipids with different core chains. A high-affinity binding of LT-IIb B-subunits to gangliosides with a neolacto core chain, such as Neu5Gcα3- and Neu5Acα3-neolactohexaosylceramide, and Neu5Gcα3- and Neu5Acα3-neolactooctaosylceramide was detected. An LT-IIb-binding ganglioside was isolated from human small intestine and characterized as Neu5Acα3-neolactohexaosylceramide. The crystal structure of the B-subunit of LT-IIb with the pentasaccharide moiety of Neu5Acα3-neolactotetraosylceramide (Neu5Ac-nLT: Neu5Acα3Galβ4GlcNAcβ3Galβ4Glc) was determined providing the first information for a sialic-binding site in this subfamily, with clear differences from that of CT and LT-I.
authors: Institute of Biomedicine, Department of Medical Biochemistry and Cell Biology, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden.
authors: Dani
authors: D
authors: Zalem
authors: Centre de Recherches sur les Macromolécules Végétales (UPR5301, CNRS and University Grenoble Alpes), BP53, F-38041 Grenoble Cedex 09, France.
authors: João P
authors: JP
authors: Ribeiro
authors: Centre de Recherches sur les Macromolécules Végétales (UPR5301, CNRS and University Grenoble Alpes), BP53, F-38041 Grenoble Cedex 09, France.
authors: Annabelle
authors: A
authors: Varrot
authors: Institute of Biomedicine, Department of Medical Microbiology and Immunology, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden.
authors: Michael
authors: M
authors: Lebens
authors: Centre de Recherches sur les Macromolécules Végétales (UPR5301, CNRS and University Grenoble Alpes), BP53, F-38041 Grenoble Cedex 09, France.
authors: Anne
authors: A
authors: Imberty
authors: Institute of Biomedicine, Department of Medical Biochemistry and Cell Biology, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden.
authors: Susann
authors: S
authors: Teneberg
mesh_terms: D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D004768:Enterotoxins / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D005732:Gangliosides / Q000737:chemistry / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012794:Sialic Acids / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D005732:Gangliosides; D012794:Sialic Acids; C027538:heat-labile enterotoxin, E coli
keywords: carbohydrate-binding site; sialic acid binding; toxin B-subunit