This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Potassium channels conduct K+ ions across the membrane of cells. Potassium conduction mediates a wide range of cellular processes including cell volume regulation, hormone secretion, and electrical signal production by nerve and muscle cells. We are focused on the mechanisms by which K+ channels open and close, the process know as gating, by external stimuli such as changes in the cell membrane voltage. We have recently determined the structure of a eukaryotic voltage-dependent K+ channel in the open conformation. We aim to determine the structure of the closed state to further our understanding of how membrane voltage controls opening in this kind of channel. In addition, we would like to determine structures with various ligands including toxins and voltage sensor inhibitors that will advance our understanding of the pharmacology of voltage-dependent potassium channels. We also have developed crystals of a G-protein regulated ion channel. The voltage-gated channel and the G-protein regulated channel will be the main foci of our synchrotron work.