Imaging and manipulation of reconstituted high-density lipoproteins under physiological conditions using atomic force microscopy

We have used atomic force microscopy (AFM) under physiological conditions to study discoidal reconstituted high density lipoproteins (rHDL). AFM can be used to obtain novel information about the structure, behavior, and function of these lipoproteins. Imaging under physiological conditions does not result in the rouleaux artifact seen in negative stain transmission electron microscopy: The thickness and structure we observe is consistent with a phospholipid bilayer. Careful high resolution measurements of particle diameters has indicated that rHDL rearrange when adsorbed to the mica surface, resulting in a mixed population consisting of the initial, reconstituted disks and larger products. The size of the larger products is consistent with a continued role for apoA-I in stabilizing certain discoidal sizes over others. The combination of AFM with monoclonal antibodies has revealed new information about the lipid bound structure of apolipoprotein A-I. Supported by grants from the National Institutes of Health GM31756 (SGS) and HL16059 (AJ) and a Molecular Biophysics Training Grant (JWC).