Part II: Diffraction from Two-Dimensional Cholera Toxin Crystals Bound to Their Receptors in a Lipid Monolayer

The structure of cholera toxin (CTAB 5) bound to its putative ganglioside receptor, galactosyl- N-acetylgalactosaminyl ( N-acetyl-neuraminyl) galactosylglucosylceramide (GM 1), in a lipid monolayer at the air-water interface has been studied utilizing grazing incidence x-ray diffraction. Cholera tox...

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Bibliographic Details
Published in:Biophysical journal 2008-07, Vol.95 (2), p.641-647
Main Authors: Miller, C.E., Majewski, J., Watkins, E.B., Weygand, M., Kuhl, T.L.
Format: Article
Language:English
Subjects:
Cholera
Cholera Toxin - chemistry
Diffraction
Galactosylceramides - chemistry
Grazing incidence
Lipid Bilayers - chemistry
Lipids
Membrane Fluidity
Membranes
Molecular Conformation
Order disorder
Phase Transition
Proteins
Reduction
Toxins
X-Ray Diffraction
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Summary:The structure of cholera toxin (CTAB 5) bound to its putative ganglioside receptor, galactosyl- N-acetylgalactosaminyl ( N-acetyl-neuraminyl) galactosylglucosylceramide (GM 1), in a lipid monolayer at the air-water interface has been studied utilizing grazing incidence x-ray diffraction. Cholera toxin is one of very few proteins to be crystallized in two dimensions and characterized in a fully hydrated state. The observed grazing incidence x-ray diffraction Bragg peaks indicated cholera toxin was ordered in a hexagonal lattice and the order extended 600–800 Å. The pentameric binding portion of cholera toxin (CTB 5) improved in-plane ordering over the full toxin (CTAB 5) especially at low pH. Disulfide bond reduction (activation of the full toxin) also increased the protein layer ordering. These findings are consistent with A-subunit flexibility and motion, which cause packing inefficiencies and greater disorder of the protein layer. Corroborative out-of-plane diffraction (Bragg rod) analysis indicated that the scattering units in the cholera layer with CTAB 5 shortened after disulfide bond reduction of the A subunit. These studies, together with Part I results, revealed key changes in the structure of the cholera toxin-lipid system under different pH conditions.
ISSN:0006-3495
1542-0086
DOI:10.1529/biophysj.107.120808