J. Biol. Chem., Vol. 262, Issue 11, 5100-5105, Apr, 1987
Neutron scattering analysis of bacterial lipopolysaccharide phase structure. Changes at high pH
JB Hayter, M Rivera and EJ McGroarty
The aggregate structure of lipopolysaccharide isolated from an Re strain of
Escherichia coli was examined at different pH values using small angle
neutron scattering. At pH values of 6 and 7.4, angle- averaged scattering
of the sodium salt of this isolate was consistent with randomly coiled
tubular micelles approximately 100 A in diameter. At pH 9.1, however,
Kratky analysis of the scattering data was distinctly different and
consistent with pairing of uniform tubular micelle sections of length 1440
and 110 A in diameter. Contrast variation measurements of the micelles
yielded an average micellar weight of the sample at pH 9.1 of approximately
1.11 X 10(7) daltons and suggested that the aggregates were tubular
micelles of size and length similar to that derived from the scattering
intensity data. Anisotropic scattering patterns of samples under shear
indicated a rigidification of the micelles as the pH was increased to 9.1
and the temperature decreased from 25 to 10 degrees C. The rotational
diffusion constants deduced from the observed shear anisotropy indicate
that the structure at pH 9.1 must have smallest and largest dimensions
which differ by at least an order of magnitude, ruling out spherical or
moderately ellipsoidal structures. Analysis of the shear rate needed to
induce anisotropic scattering indicated that the stiffness length of the
micelles at pH 9.1 was approximately 1000 A and decreased at higher and
lower pH values.
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