Designing an Integrated Nanoscale System for Ion Channel Structure-Function Study

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DESCRIPTION (provided by applicant): Overall goal of this application is to design and develop nanotechnology to study key nanoscale biostructures - Ion channels and receptors that are essential for all living functions. Changes in their three-dimensional (3D) structure and activity, in response to stimuli related to life style, including drug addiction, trigger severe health abnormalities. Understanding 3D structure-activity relationship of these nano-biostructures has been a central and yet elusive goal. 3D structure is currently examined with time and resource limiting X-ray diffraction and EM. Ion channel activity is analyzed by patch clamping and fluorescence microscopy. However, there is no integrated system for a direct 3D structure-activity study of these nano-biostructures in aqueous buffer. Atomic force microscopy (AFM) provides high resolution structural information, in aqueous medium, for many macromolecular complexes, including channels and receptors. AFM is ideally suited to image the surface topology - the primary structural domain where external stimuli, including drug molecules would normally interact. Open architecture of AFM permits integration of other techniques. An integrated multimodal AFM would allow real-time imaging of channel (or receptor)-stimuli (or perturbants) complex, their physicochemical properties and resulting channel conformations. We propose to design a state-of-the-art double chamber AFM integrated with high resolution imaging and permeability assay tools. As a test of its applications related to NIDA's mission, a potential supporter of this application, we will study two important ion channels: hemichannels and Acetyl choline receptor (AChR) that are intimately related to drug addiction. Their 3D structure and their permeability to ions and signaling molecules, in response to drug addiction-inducing stimuli will be examined. Hemichannels connect a cell to its extracellular milieu or its neighbor cells. They are linked to smoking-induced cell pathology and their presence is modulated by drug addiction-related cell receptors (e.g., dopamine receptor) and stimuli. Specific Aims of the application are: 1. Design a combined AFM, Support silicon Chip with a nanopore, TIRF, Single molecule FRET and voltage-sensitive dye imaging systems. As a test of this system, image 3D structure of hemichannels and AChR. 2a. Examine molecular permeability and ionic conductance, in response to physiological and drug addiction-related stimuli. This includes, a) measuring channel permeability to ions, sensor dyes and signaling molecules and b) examining role of defined gating agents and drug addiction-related perturbations, including smoking condensate, nicotine and ROS on the channel permeability, and 2b. Examine density, distribution and turnover of hemichannels and AChR (a drug addiction related receptor) in single cell plasma membrane in response to drugs (e.g., cocaine, nicotine) and pathological agents. The integrated imaging system developed in this study will be first of its kind and will have far reaching and broader role in defining our understanding of the molecular determinants of drug addiction, their pathological consequences as well as in development of therapeutics for drug addiction and treatment. PUBLIC HEALTH RELEVANCE: Consequences of drug addictions on human health and society at large are considerable, yet there is a limited understanding of the underlying mechanism(s) of the cause and/or deleterious effects of these addictions. Most of the drug addiction stimuli possibly induce their effects through them modulating the structure and activity of ion channels and receptors such as acetyl choline receptor (AChR) and gap junctional hemichannels. Currently there is no experimental tool to measure simultaneously an ion channel activity while imaging its 3D molecular structure, the 3D conformations; yet this is the kind of information that is essential to advance our understanding of the molecular mechanism underlying drug addiction and/or their pathological consequences. Advances in nanoscience and technology provide perhaps, the best avenue to explore complex pathological processes that are mediated by nanoscale biostructures, such as ion channels and receptors. Here we intend to implement the most advanced integrated multimodal tools and test their applications on two major classes of ion channels, hemichannels and AChR. Our successful completion of the proposed undertaking will be like combining EM with patch clamping and single molecule imaging that fill the void as well as will provide viable avenues for development of therapeutics for drug addiction and treatment.