PMID:7768810

Citation	Jemal, C, Haddad, JE, Begum, D and Jackson, MP (1995) Analysis of Shiga toxin subunit association by using hybrid A polypeptides and site-specific mutagenesis. J. Bacteriol. 177:3128-32
Abstract	Shiga toxin (STX), a bacterial toxin produced by Shigella dysenteriae type 1, is a hexamer composed of five receptor-binding B subunits which encircle an alpha-helix at the carboxyl terminus of the enzymatic A polypeptide. Hybrid toxins constructed by fusing the A polypeptide sequences of STX and Shiga-like toxin type II were used to confirm that the carboxyl terminus of the A subunits governs association with the B pentamers. The alpha-helix of the 293-amino-acid STX A subunit contains nine residues (serine 279 to methionine 287) which penetrate the nonpolar pore of the B-subunit pentamer. Site-directed mutagenesis was used to establish the involvement of two residues bordering this alpha-helix, aspartic acid 278 and arginine 288, in coupling the C terminus of StxA to the B pentamer. Amino acid substitutions at StxB residues arginine 33 and tryptophan 34, which are on the membrane-contacting surface of the pentamer, reduced cytotoxicity without affecting holotoxin formation. Although these B-subunit mutations did not involve receptor-binding residues, they may have induced an electrostatic repulsion between the holotoxin and the mammalian cell membrane or disrupted cytoplasmic translocation.
Links	PubMed PMC177002
Keywords	Amino Acid Sequence; Bacterial Toxins/chemistry; Base Sequence; DNA Primers/chemistry; Genetic Complementation Test; Molecular Sequence Data; Mutagenesis, Site-Directed; Protein Binding; Recombinant Proteins; Shiga Toxins; Shigella dysenteriae/pathogenicity; Structure-Activity Relationship
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
SHIDY:STXB		GO:0009405: pathogenesis	ECO:0000315:		P		Table 4.	complete

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