Cryo-EM, X-ray crystallography, and electrophysiology to study ion channelsElectrical 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.
The Type 3 Ryanodine Receptor (RyR3) is a large ER-resident calcium channel that plays a critical role various tissues, including neurons where it is involved in learning and memory. We solved high-resolution cryo-EM structures of RyR3 in different conformational states. RyR3 has unique functional properties leading to a high gain of calcium release. We identified binding sites for chloride and ATP in the N-terminal region and an altered interface with an auxiliary protein known as FKBP12/12.6. Our work suggests a direct link with epileptic encephalopathy, likely caused by mutations in RyR3.
https://www.nature.com/articles/s41467-024-52998-9 
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