Crystallographic analysis of freeze-fracture electron micrographs: application to the structure determination of cubic lipid-water phases

摘要

An original approach combining freeze-fracture electron microscopy and quantitative image processing has been developed as an alternative to X-ray analysis. It has been applied to the crystallographic study of different lipid-water cubic phases [bicontinuous or micellar and of type I (oil-in-water) or type II (water-in-oil)] and has enabled significant advances in the study of these phases, Freeze-fracture electron microscopy has revealed that the cubic phases fracture preferentially along a few crystallographic directions which appeared on the images as noisy planar fracture surfaces containing periodic information. The visibility of the corresponding unit cells has been considerably improved by image-filtering techniques based on correlation averaging, allowing a quantitative analysis of the fracture images to be made. This analysis yielded faithful information on the symmetries of the cubic structure (rotation axes and mirror planes) as well as on the structure of the cubic phase itself, Eventually, the different parameters that determine the most favourable fracture pathways within the structures were established. This novel approach constitutes a powerful tool of general interest, complementary to X-ray diffraction, for solving complex ordered macromolecular structures at low resolution. [References: 39]