title: Alterations at the carboxyl terminus change assembly and secretion properties of the B subunit of Escherichia coli heat-labile enterotoxin.
abstract: The gene encoding the B subunit of heat-labile enterotoxin (etxB) was mutated at its 3' end by targeted addition of random nucleotide sequences. Gene products from five mutated etxB genes, all of which were shown to encode B subunits with short carboxy-terminal amino acid extensions, were analyzed with respect to a range of functional and structural properties. One class of altered B subunits, exemplified by EtxB124 and EtxB138, which both have seven extra amino acid residues, were found to be specifically defective in their ability to stably associate with A subunits and form holotoxin. Other altered B subunits were less subtlely affected by extensions at their C termini and were, in addition to their failure to associate with A subunits, unable to translocate into the periplasm of Escherichia coli, to pentamerize, or to bind to GM1 ganglioside. This suggests that the carboxy-terminal domain of EtxB mediates A subunit-B subunit interaction.
authors.affiliation: Institute for Applied Cell and Molecular Biology, Umeå University, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Sandkvist
authors.forename: T R
authors.initials: TR
authors.lastname: Hirst
authors.forename: M
authors.initials: M
authors.lastname: Bagdasarian
mesh_terms: D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002772:Cholera Toxin / Q000276:immunology; D004262:DNA Restriction Enzymes; D004269:DNA, Bacterial / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D004768:Enterotoxins / Q000235:genetics* / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D005677:G(M1) Ganglioside / Q000378:metabolism; D005798:Genes, Bacterial; D006801:Humans; D007118:Immunoassay; D008969:Molecular Sequence Data
chemical_list: D001427:Bacterial Toxins; D004269:DNA, Bacterial; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D005677:G(M1) Ganglioside; D002772:Cholera Toxin; C027538:heat-labile enterotoxin, E coli; D004262:DNA Restriction Enzymes