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Structural studies of receptor binding by cholera toxin mutants.
- Source :
-
Protein science : a publication of the Protein Society [Protein Sci] 1997 Jul; Vol. 6 (7), pp. 1516-28. - Publication Year :
- 1997
-
Abstract
- The wide range of receptor binding affinities reported to result from mutations at residue Gly 33 of the cholera toxin B-pentamer (CTB) has been most puzzling. For instance, introduction of an aspartate at this position abolishes receptor binding, whereas substitution by arginine retains receptor affinity despite the larger side chain. We now report the structure determination and 2.3-A refinement of the CTB mutant Gly 33-->Arg complexed with the GM1 oligosaccharide, as well as the 2.2-A refinement of a Gly 33-->Asp mutant of the closely related Escherichia coli heat-labile enterotoxin B-pentamer (LTB). Two of the five receptor binding sites in the Gly 33-->Arg CTB mutant are occupied by bound GM1 oligosaccharide; two other sites are involved in a reciprocal toxin:toxin interaction; one site is unoccupied. We further report a higher resolution (2.0 A) determination and refinement of the wild-type CTB:GM1 oligosaccharide complex in which all five oligosaccharides are seen to be bound in essentially identical conformations. Saccharide conformation and binding interactions are very similar in both the CTB wild-type and Gly 33-->Arg mutant complexes. The protein conformation observed for the binding-deficient Gly 33-->Asp mutant of LTB does not differ substantially from that seen in the toxin:saccharide complexes. The critical nature of the side chain of residue 33 is apparently due to a limited range of subtle rearrangements available to both the toxin and the saccharide to accommodate receptor binding. The intermolecular interactions seen in the CTB (Gly 33-->Arg) complex with oligosaccharide suggest that the affinity of this mutant for the receptor is close to the self-affinity corresponding to the toxin:toxin binding interaction that has now been observed in crystal structures of three CTB mutants.
- Subjects :
- Animals
Carbohydrates chemistry
Cholera Toxin metabolism
Crystallography, X-Ray
Escherichia coli chemistry
Escherichia coli pathogenicity
G(M1) Ganglioside metabolism
Humans
Hydrogen Bonding
Models, Molecular
Mutagenesis, Site-Directed
Protein Binding
Protein Conformation
Receptors, Cell Surface metabolism
Surface Properties
Swine
Bacterial Toxins chemistry
Cholera Toxin chemistry
Cholera Toxin genetics
Enterotoxins chemistry
Escherichia coli Proteins
G(M1) Ganglioside chemistry
Mutation
Receptors, Cell Surface chemistry
Subjects
Details
- Language :
- English
- ISSN :
- 0961-8368
- Volume :
- 6
- Issue :
- 7
- Database :
- MEDLINE
- Journal :
- Protein science : a publication of the Protein Society
- Publication Type :
- Academic Journal
- Accession number :
- 9232653
- Full Text :
- https://doi.org/10.1002/pro.5560060716