X-ray anomalous diffraction of lipid structures: Lamellar phase and inverted hexagonal phase
Huang, Huey W.
Master of Science
The method of X-ray multi-wavelength anomalous dispersion (MAD) is a phasing method routinely used in protein crystallography, but the same method is difficult for lipid systems for the practical reason that the commonly used lipid samples for diffraction do not have a well-defined thickness. The first chapter is devoted to a practical approach to use the MAD method for lipid structures. The procedure is demonstrated with the lamellar phase of a brominated lipid. In the second chapter, we apply this new MAD method to an inverted hexagonal structure. The bromine distribution obtained from the MAD analysis provides the information for the chain packing in the hexagonal unit cell. The intensity of the bromine distribution is undulated around the unit cell. The analysis shows that the lipid chains pack the hexagonal unit cell at constant volume per chain, with no detectable effect from a high-energy interstitial region.