title: Escherichia coli heat-labile enterotoxin binds to glycosylated proteins with lactose by amino carbonyl reaction.
abstract: The binding of Escherichia coli heat-labile enterotoxin (LT) type I to glycosylated proteins with lactose (Gal beta 1-4Glc) by amino carbonyl reaction was studied by the Western blot assay and by the microtiter well binding assay. LT bound to a lactose-alpha-lactalbumin amino carbonyl product (Lac-LA), whereas cholera toxin did not. The binding ability of Lac-LA was abolished by beta-galactosidase treatment, indicating that the terminal galactose is essential for the binding of LT. The binding of LT to Lac-LA was inhibited by galactose and lactose, and most effectively inhibited by lactulose (Gal beta 1-4Fru), which is a structural analog of the Amadori rearrangement product of the amino carbonyl reaction between lactose and an epsilon-amino group of a lysine residue (lactuloselysine). The results suggest that LT recognizes the portion of lactuloselysine in Lac-LA. LT also bound to a melibiose (Gal alpha 1-6Glc)-alpha-lactalbumin amino carbonyl product (Mel-LA), but the binding ability of Mel-LA was weaker than that of Lac-LA, suggesting that the beta 1-4 linked terminal galactose is dispensable but preferable for the binding. Furthermore, LT bound to the amino carbonyl products of lactose with beta-lactoglobulin, caseins, bovine serum albumin, and ovalbumin. These results indicate that LT binds to the amino carbonyl products between proteins and sugars containing the terminal galactose, such as lactose.
authors.affiliation: Yakult Central Institute for Microbiological Research, Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Shida
authors.forename: K
authors.initials: K
authors.lastname: Takamizawa
authors.forename: M
authors.initials: M
authors.lastname: Nagaoka
authors.forename: T
authors.initials: T
authors.lastname: Tsuji
authors.forename: T
authors.initials: T
authors.lastname: Osawa
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D015153:Blotting, Western; D002772:Cholera Toxin / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004768:Enterotoxins / Q000378:metabolism*; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D006023:Glycoproteins / Q000378:metabolism*; D006031:Glycosylation; D007768:Lactalbumin / Q000378:metabolism; D007785:Lactose / Q000378:metabolism*; D011817:Rabbits
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D006023:Glycoproteins; D002772:Cholera Toxin; D007768:Lactalbumin; C027538:heat-labile enterotoxin, E coli; D007785:Lactose