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 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 A. 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.
Miller
C E
CE
Manuel Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico, USA.
Majewski
J
J
Watkins
E B
EB
Weygand
M
M
Kuhl
T L
TL
D002772:Cholera Toxin / Q000737:chemistry*; D005699:Galactosylceramides / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008968:Molecular Conformation; D044367:Phase Transition; D014961:X-Ray Diffraction
D005699:Galactosylceramides; D008051:Lipid Bilayers; D002772:Cholera Toxin