Fukuta S, Magnani J L, Twiddy E M, Holmes R K, Ginsburg V
Laboratory of Structural Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Infect Immun. 1988 Jul;56(7):1748-53. doi: 10.1128/iai.56.7.1748-1753.1988.
The heat-labile enterotoxins of Vibrio cholerae and Escherichia coli are related in structure and function. They are oligomers consisting of A and B polypeptide subunits. They bind to gangliosides, and they activate adenylate cyclase. The toxins form two antigenically distinct groups; members of each group cross-react but are not necessarily identical. Serogroup I includes cholera toxin (CT) and type I heat-labile enterotoxin (LT-I) of E. coli. LTh-I and LTp-I are antigenic variants of LT-I produced by strains of E. coli from humans and pigs, respectively. Serogroup II contains the type II heat-labile enterotoxin (LT-II) of E. coli. Two antigenic variants designated LT-IIa and LT-IIb have been described. The binding of CT, LTh-I, LT-IIa, and LT-IIb to gangliosides was analyzed by immunostaining thin-layer chromatograms and by solid-phase radioimmunoassay. The four toxins have different glycolipid-binding specificities. LTh-I and CT bind strongly to ganglioside GM1 and less strongly to ganglioside GD1b. However, LTh-I, unlike CT, also binds weakly to GM2 and asialo GM1. LTh-I, like CT, probably binds to the terminal sugar sequence Gal beta 1-3GalNAc beta 1-4(NeuAc alpha 2-3)Gal . . ., where GalNAc is N-acetylgalactosamine and NeuAc is N-acetylneuraminic acid. LT-IIa probably binds to the same sugar sequence to which CT and LTh-I bind, with the additional contribution to binding of a second NeuAc as in GD1b and GD2. Also, LT-IIa must bind the Gal beta 1-3GalNAc . . . sequence in such a way that its binding is relatively unaffected by attachment of NeuAc to the terminal galactose residue as in GD1a, GT1b, and GQ1b. LT-IIb probably binds to the terminal sugar sequence NeuAc alpha 2-3Gal beta 1-4GalNAc . . ., as it binds to gangliosides GD1a and GT1b but not to GM1.
霍乱弧菌和大肠杆菌的不耐热肠毒素在结构和功能上相关。它们是由A和B多肽亚基组成的寡聚体。它们与神经节苷脂结合，并激活腺苷酸环化酶。这些毒素形成两个抗原性不同的组；每组的成员会发生交叉反应，但不一定完全相同。血清群I包括霍乱毒素（CT）和大肠杆菌的I型不耐热肠毒素（LT-I）。LTh-I和LTp-I分别是由来自人类和猪的大肠杆菌菌株产生的LT-I的抗原变体。血清群II包含大肠杆菌的II型不耐热肠毒素（LT-II）。已描述了两种名为LT-IIa和LT-IIb的抗原变体。通过免疫染色薄层色谱法和固相放射免疫分析法分析了CT、LTh-I、LT-IIa和LT-IIb与神经节苷脂的结合。这四种毒素具有不同的糖脂结合特异性。LTh-I和CT与神经节苷脂GM1强烈结合，与神经节苷脂GD1b的结合较弱。然而，与CT不同，LTh-I也与GM2和脱唾液酸GM1弱结合。LTh-I与CT一样，可能与末端糖序列Galβ1-3GalNAcβ1-4（NeuAcα2-3）Gal...结合，其中GalNAc是N-乙酰半乳糖胺，NeuAc是N-乙酰神经氨酸。LT-IIa可能与CT和LTh-I结合的相同糖序列结合，如在GD1b和GD2中一样，第二个NeuAc对结合有额外贡献。此外，LT-IIa必须以这样一种方式结合Galβ1-3GalNAc...序列，即其结合相对不受NeuAc连接到末端半乳糖残基（如在GD1a、GT1b和GQ1b中）的影响。LT-IIb可能与末端糖序列NeuAcα2-3Galβ1-4GalNAc...结合，因为它与神经节苷脂GD1a和GT1b结合，但不与GM1结合。
