Fluid bilayer structure determination: Joint refinement in composition space using X-ray and neutron diffraction data
- Univ. of California, Irvine, CA (United States)
- Univ. of California, San Francisco, CA (United States)
Experimentally-determined structural models of fluid lipid bilayers are essential for verifying molecular dynamics simulations of bilayers and for understanding the structural consequences of peptide interactions. The extreme thermal motion of bilayers precludes the possibility of atomic-level structural models. Defining {open_quote}the structure{close_quote} of a bilayer as the time-averaged transbilayer distribution of the water and the principal lipid structural groups such as the carbonyls and double-bonds (quasimolecular fragments), one can represent the bilayer structure as a sum of Gaussian functions referred to collectively as the quasimolecular structure. One method of determining the structure is by neutron diffraction combined with exhaustive specific deuteration. This method is impractical because of the expense of the chemical syntheses and the limited amount of neutron beam time currently available. We have therefore developed the composition space refinement method for combining X-ray and minimal neutron diffraction data to arrive at remarkably detailed and accurate structures of fluid bilayers. The composition space representation of the bilayer describes the probability of occupancy per unit length across the width of the bilayer of each quasimolecular component and permits the joint refinement of X-ray and neutron lamellar diffraction data by means of a single quasimolecular structure that is fitted simultaneously to both data sets. Scaling of each component by the appropriate neutron or X-ray scattering length maps the composition-space profile to the appropriate scattering length space for comparison to experimental data. The difficulty with the method is that fluid bilayer structures are generally only marginally determined by the experimental data. This means that the space of possible solutions must be extensively explored in conjunction with a thorough analysis of errors.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- OSTI ID:
- 381085
- Report Number(s):
- LA-UR-96-634; CONF-9410223-; ON: DE96006681; TRN: 96:005198-0018
- Resource Relation:
- Conference: 3. conference on neutrons in biology, Santa Fe, NM (United States), 24-28 Oct 1994; Other Information: PBD: [1994]; Related Information: Is Part Of Proceedings of the neutrons in biology conference, Santa Fe, NM, October 1994; Schoenborn, B.P.; PB: 354 p.
- Country of Publication:
- United States
- Language:
- English
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