Morphology of native and reconstituted biological membranes and their components analysed with atomic force microscopy

The atomic force microscope can image the three-dimensional surface structure of soft biological membranes and their components in a physiological environment. Living macrophages prior to and after particle phagocytosis allowed low-resolution images by AFM. An active change of cell shape by mechanical stimulation is observed. Indentation depths of 1-30 nm were derived as function of cell preparation. High-resolution images were achieved for TexasRed IgG antibodies specifically bound to a mica-supported planar phospholipid bilayer doped with phospholipids containing headgroups of TexasRed. The cloned nicotinic acetylcholine receptor (nAChR) expressed in Xenopus oocytes were m aged at molecular resolution. An unambiguous identification of individual single nAChR proteins is hindered by the pres ence of endogenous membrane proteins. For the first time we introduce a favorable membrane system: the vacuolar membrane of plant cells, which allows the molecular identification of integral endogenous membrane proteins and a structural analysis of the lipid matrix.