Cryo-EM, X-ray crystallography, and electrophysiology to study ion channels

Electrical signals are the fastest ways to relay information within and across cells. In electrically excitable cells, ion channels are responsible for these signals, playing essential roles in neuronal signaling, the beating of our hearts, the contraction of muscle, the release of hormones, and much more. Ion channel genes are affected by thousands of genetic variants that result in 'channelopathies', a set of severe disorders ranging from inherited cardiac arrhythmias to chronic pain, autism and congenital epilepsy. Faulty regulation of ion channels, through aberrant post-translational modifications, also causes or contributes to non-genetic disorders, including atrial fibrillation and Alzheimer's disease. 

A fascinating property of ion channels is their ability to 'gate': they can open, close, or inactivate under the influence of various stimuli. They can thus sense temperature, mechanial pressure, and differences in membrane potentials, as well as small molecule ligands and post-translational modifications. Many ion channels are part of larger complexes that are either stable or dynamic.  We investigate these properties via various methods, and analyze how disease-causing mutations change their function. 

As ion channels are complex and dynamic proteins, we utilize a combination of structural and functional methods. This includes cryo-electron microscopy and X-ray crystallography to study their 3D structures, and electrophysiology to measure the electrical currents generated when ions permeate open channels.

Visualizing a channelopathy. The Type 1 Ryanodine Receptor is the target for mutations causing malignant hyperthermia (MH) and central core disease (CCD).  The R615C mutation is causative for MH. A cryo-EM study shows how a single point mutation triggers large conformational changes that lead to facilitated channel opening. In combination with volatile anesthetics, such mutations can have deadly consequences. Similar mechanisms underlie cardiac arrhythmias in the Type 2 Ryanodine Receptor.

https://www.nature.com/articles/s41467-021-21141-3

David vs Goliath: How a small 33-residue peptide takes control of a ~20,000-residue membrane protein...

​Pandinus imperator, a.k.a. the emperor scorpion, produces a venomous peptide known as imperacalcin. This peptide can cross the plasma membrane and gain access to an intracellular target: the Ryanodine Receptor. Our cryo-EM study shows imperacalcin (green) binding adjacent to the transmembrane region of this ion channel, where it causes a partial reduction in ionic flow, causing a 'subconductance', easily visible in single channel electrophysiology recordings ('S').  It also holds the channel in an open conformation and breaks the 4-fold symmetry. 

https://www.science.org/doi/10.1126/sciadv.adf4936