title: Preferred orientations of LDL in vitreous ice indicate a discoid shape of the lipoprotein particle.
abstract: The structure of the human low-density lipoprotein (LDL) was analyzed in vitreous ice using cryo-electron microscopy (cryo-EM). In relatively thick cryo-EM preparations, random orientation of LDL particles produced various types of projections on the microscope screen, including circular projections with a high-density ring and rectangular projections with two high-density bands. However, in especially thin preparations, preferred, non-random orientations of the LDL particle produced only circular projections of the lipoprotein structure. In preparations with high LDL concentrations, ordered two-dimensional arrays, including hexagonal arrangements of circular projections and short stacks of rectangular projections, were observed. These observations are consistent with a discoid shape of the LDL particle, and suggest that surface tension forces may influence orientation of the LDL disc in thin aqueous films. Face-on orientation of LDL in especially thin cryo-EM preparations may explain earlier difficulties in identifying discoid features of the lipoprotein particle, and illustrates that some caution is warranted when attempts are made to reconstruct the three-dimensional structure of LDL from cryo-electron micrographs.
authors.affiliation: Department of Biochemistry, Medical College of Virginia Campus, Virginia Commonwealth University, P.O. Box 980614, Richmond, VA 23298, USA. hgvanant@hsc.vcu.edu
authors.forename: Rik
authors.initials: R
authors.lastname: van Antwerpen
mesh_terms: D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000737:chemistry; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D006801:Humans; D007053:Ice; D008074:Lipoproteins / Q000737:chemistry; D008075:Lipoproteins, HDL / Q000737:chemistry; D008077:Lipoproteins, LDL / Q000737:chemistry* / Q000648:ultrastructure; D013696:Temperature
chemical_list: D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D007053:Ice; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL