Voltage-dependent ion channels are instrumental in the generation of membrane potential, receptor potential, and action potential. They are implicated in the physiology and pathophysiology of all excitable tissues. These proteins underlie many disease processes including arrhythmias and epilepsies and are major targets of essential drugs used in clinical medicine. Despite the obvious biological and clinical importance of these proteins, very little is known about their structure. Obtaining this structural information is of paramount importance to a mechanistic understanding of their function. This proposal presents a new approach toward addressing the structure and function of these proteins. Bacterial model systems will be studied by two complimentary techniques: site-directed spin labeling and electrophysiology. The study will address two key properties of potassium channels: permeation and gating. It is thought that the structural elements underlying permeation and, to some extent, gating have been identified. All cation selective voltage-dependent ion channels share a common core domain that is sufficient for ion permeation. Also, a highly unusual transmembrane segment known as S4 has been implicated as part of the structural element responsible for voltage-dependent gating. These two structural elements will be studied with the two techniques. It is anticipated that the results of the spin labeling study will provide sufficient constraints to determine the structure of these two elements to the level of the backbone fold. The resulting folding model will provide the basis for a mechanistically inspired functional study using electrophysiology. The long-term goal of this proposal is to understand functional properties of ion channels at a structural level.
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