Crystallization of human low density lipoprotein (LDL), a large lipid-protein complex : collection of X-ray data at very low resolution

Abstract

Human LDL subfractions LDL-2 (d=1.031-1.034 g/ml) and LDL-5 (d=1.040-1.044 g/ml) were crystallized in different crystal forms using polyethylene glycol as a precipitant. Both fractions were from one donor. Crystals of LDL-5 were yellow, hexagonal, and showed no dichroism. Of LDL-2 two dichroitic crystal forms were obtained. One had a rod-like shape with deep notches at both ends (form A), the other was a more compact form with plain surfaces (form B). To be able to measure low order reflections down to 300 Å a special experimental setup was developed. One single crystal was used to obtain a complete native data set of LDL-2 (form A) with an overall internal R-factor of 4.5% for reflections from 100 to 28 Å. Data were collected under cryogenic conditions using synchrotron radiation. The space group is most probably C2 with unit cell dimensions of a=183 Å, b=421 Å, c=385 Å, α=γ=90°, β≈90°. Further optimization of the crystallization conditions and the search for heavy metal derivatives are in progress.