21 research outputs found
Electron density modeling and reconstruction of infinite periodic minimal surfaces (IPMS) based phases in lipid-water systems. II. Reconstruction of D surface based phases
This is the second of two papers dealing with the structure of
lipid-water phases based on Infinite Periodic Minimal Surfaces
(IPMS). The first paper describes mathematical modeling of such
phases. In this paper, a new reconstruction method, called the
methyl trough search, is described and used to solve the
structures based on powder pattern X-ray diffraction data.
Structures are derived for both a single chain lipid-water system
(mono-olein) and a diacyl phospholipid-water system (2-2 methyl
butyl 16:0 phosphatidylcholine). The methyl trough search uses
the low electron density of the lipid methyl tails to determine
the correct phasing for the electron density reconstruction. The
data are consistent with a structure based on the IPMS D surface.
The results are compared to other methods used to solve the
mono-olein structure; the structure of the diacyl lipid has never
before been solved. We discuss the subtleties involved in
reconstruction of D surface based phases and the substantial
artifacts that arise in low-resolution reconstructions of
hydrocarbon lipids lacking heavy-atom sites