Low-resolution data analysis for low-density lipoprotein particle

The knowledge of the molecular structure of LDL, a large lipoprotein comple x, is of great interest for medical investigations. Currently available LDL crystals do not diffract to high resolution and do not allow the applicati on of standard crystallographic techniques. Additional difficulties arise b ecause of a very dense crystal packing and the presence of several componen ts with quite different mean densities. Several ab initio phasing methods p reviously reported by the authors have been successfully applied to rnd a c rystallographic image of LDL at a resolution of 27 Angstrom. The most promi sing results have been obtained using direct phasing with a connectivity an alysis of the electron-density maps. The current image makes it possible to discern a single particle covered by a layer of relatively high density th at is asymmetrically distributed on the particle surface. It shows a partit ion of high and low densities inside the particle and, in particular, strip s of varying density in the lipid core.