Biophysical Journal 60: 1178-1189 (1991)
© 1991 the Biophysical Society

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Orienting rigid and flexible biological assemblies in ferrofluids for small-angle neutron scattering studies

T. Sosnick ^*, S. Charles , G. Stubbs , P. Yau ^||, E. M. Bradbury ^* ||, P. Timmins ^¶ and J. Trewhella ^*

Life Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
Department of Chemistry, University College of North Wales, Bangor Gwynedd, Wales
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee
Department of Biological Chemistry, University of California at Davis, California USA
Institut Laue-Langevin, Grenoble Cedex, France

ABSTRACT

Small-angle scattering from macromolecules in solution is widely used to study their structures, but the information content is limited because the molecules are generally randomly oriented and hence the data are spherically averaged. The use of oriented rodlike structures for scattering, as in fiber diffraction, greatly increases the amount of structural detail that can be obtained. A new technique using a ferromagnetic fluid has been developed to align elongated structures independent of their intrinsic magnetic properties. This technique is ideal for small-angle neutron scattering because the scattering from the ferrofluid particles can be reduced significantly by matching the neutron scattering length density of the particles to a D₂O solvent ("contrast matching"). The net result is scattering primarily from the ordered biological assembly in a solution environment that can be adjusted to physiological pH and ionic strength. Scattering results from ordered tobacco mosaic virus, tobacco rattle virus, and chromain fibers are presented.