CFN Virtual Colloquium

Cryo-Electron Microscopy (cryo-EM) is a powerful high-resolution structure determination technique. With the hardware and software advancement, atomic resolution structures have been routinely determined by cryo-EM single particle analysis (SPA). Here, cryo-EM SPA has been employed to study structures of voltage-gated ion channels. Voltage-gated ion channels sense the voltage changes across the cell membrane (i.e. membrane potential, membrane voltage) and undergo conformational changes thus to regulate the ion flux across the cell membrane. Due to their critical roles in excitable cells such as nerve and muscle, they are called life's transistors.

To understand how a voltage-gated ion channel carries out its function, it requires at least two conformational states: one with the voltage-sensor domain (VSD) in the activated (i.e. up) state and the other with the VSD in the resting (i.e. down) state. Because the VSD up state is stable in the absence of a membrane potential, many determined voltage-gated ion channel structures were in the VSD up state and only a few structures were in the VSD down state. Here, we inserted voltage-shifting mutations and introduced a disulfide crosslink in the ancestral bacterial sodium channel NaVAb. A cryo-EM structure of the resting state and a complete voltage-dependent gating mechanism has been determined. Meanwhile, we developed a random spherical constrained cryo-EM SPA method to apply membrane voltage to trap voltage-gated ion channels in VSD down state. As a proof of concept, a voltage- and calcium-activated potassium channel (BK) was reconstituted into lipid vesicles and the structure of reconstituted BK channel was determined by cryo-EM. Instead of the common four-fold symmetry observed in other ion channels, a two-fold symmetry was observed in BK, which may shine lights onto the understanding of the dynamic voltage-sensing and ligand-binding process.

Bio-sketch: Dr. Liguo Wang is a Director of Scientific Operations for LBMS of NSLS-II, a state-of-the-art cryo-electron microscopy facility for studies on the building blocks of all living organisms and their behavior. Dr. Wang joined BNL in 2019 from the Department of Biological Structure at the University of Washington, Seattle. He received his B.S. in Chemical and Environmental Engineering from Tsinghua University in 1994 and PhD in Chemical and Biomolecular Engineering from Cornell University in 2003. He conducted his postdoctoral study at Yale University before joining the University of Washington as a faculty member in 2010. He is an expert in the application of cryo-EM on biological materials.