Atomic Force Microscopy of Reconstituted Ion Channels
Ion channels and receptors are specialized biomembrane structures that serve as the interface between opposing compartments (e.g., cytoplasm and extracellular region, cytoplasm and intravesicular region) and toward which most of the regulatory signals are directed. Molecular three-dimensional (3D) structure of channels and receptors are studied primarily by high-resolution imaging techniques, including electron microscopy, electron and Xray diffractions, and infra-red spectroscopy. These techniques provide insufficient information about the surfaces of channels and receptors, the very sites of molecular interactions with external perturbations, and are usually unsuitable for combining biochemical, electrophysiological, and molecular biological techniques for simultaneous structure-function analyses. An atomic force Microscope (AFM) (1) can image the 3D-surface structure of a wide variety of native biological specimens, including reconstituted channels and receptors, in an aqueous medium and with subnanometer resolution (for reviews, see refs. 2, 3, 4). An AFM can also manipulate surfaces with molecular precision, i.e., it can nanodissect, translocate, and reorganize molecules on surfaces. AFM imaging in the hydrated condition provides an opportunity for observing biochemical and physiological processes in real time at molecular level and thus can be used for direct molecular structure-function studies. 3D surface topography has been imaged for several ion channels, pumps, and receptors that were: 1) present in isolated native membranes, 2) reconstituted in artificial membrane or, 3) expressed in an appropriate expression system. The present chapter provides a brief summary of imaging molecular structure and function of reconstituted channels and receptors using AFM.
KeywordsAtomic Force Microscope Atomic Force Microscope Imaging Bordetella Pertussis Molecular Resolution OmpF Porins
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