Ion channel structure, function, regulation, disease mechanisms and drug discovery
Ion channels are multi-subunit membrane protein complexes. They are present in every cell type and selectively conduct ions across cell membranes when activated, resulting in electrical and chemical changes in cells. As such, ion channels are essential for all our body functions. Genetic mutations in and misregulation of ion channels cause numerous human diseases and disorders, such as heart diseases, epilepsy, autism, and cancer, to name just a few.
We focus on voltage-gated calcium channels (VGCCs), transient receptor potential (TRP) channels, and cyclic nucleotide-gated (CNG) channels. Upon activation, these channels produce membrane depolarization and calcium influx; thus, they not only increase cell excitability but also affect cellular calcium signaling. VGCCs are present in neurons, muscles and other excitable cells, and they open in response to membrane depolarization. They are vital for diverse biological processes including muscle contraction, neurotransmission, neurodevelopment and gene expression. TRP channels are more ubiquitous and are activated by more diverse mechanisms, including intracellular or extracellular ligands, mechanical stretch, temperature as well as changes in membrane voltage. TRP channels are involved in virtually all physiological processes and play an especially important role in sensory physiology and immune responses. CNG channels convert light- and odorant-induced chemical signals into electrical signals in the eye and nose and are indispensable for vision and smell.
We use a combination of techniques including molecular biology, biochemistry, patch-clamp, cryo-EM and optical imaging to study the structure, function, regulation and channelopathy of VGCCs, TRP channels and CNG channels. Our objectives are to better understand how these ion channels work as molecular machines, how they function to control cell excitability and signaling, and how their mutations and malfunction cause human diseases. We also screen for compounds from traditional Chinese medicines that activate or inhibit these (and other) channels, elucidate their action mechanisms, and aim to develop new drugs targeting the channels.
Current and Future Research Projects
CNG channel structures, activation mechanisms, and disease mechanisms
In recent years we have obtained the first cryo-EM structures of a full-length eukaryotic CNG channel (TAX-4 from the nematode C. elegans) in both closed and open states and elucidated its activation mechanisms, obtained the first cryo-EM structure of the human cone photoreceptor CNG channel, and characterized a cone CNG channel disease mutation. Building on these advances, we are studying the structural basis of cooperativity of CNG channel activation and structurally and functionally elucidating the pathogenic mechanisms of a diverse set of CNG channel mutations that cause blindness or color blindness.
Structural basis of TRPML channel activation and regulation
TRPML channels function as calcium channels in endosomes and lysosomes and are crucial for cellular physiology. Mutations in TRPML1 cause mucolipidosis type IV, a rare but devastating lysosomal storage disorder in humans, and mutations in TRPML3 cause deafness and pigmentation defects in mice. In recent years we have determined high-resolution X-ray crystal structures of a functionally important domain of TRPML1 and cryo-EM structures of the full-length TRPML3 under various conditions or in different states. We are now determining the structures of TRPML2 in different conditions. Our results reveal that human TRPML2, which plays a unique role in immune responses and is much less studied, exhibits features and properties that are distinct from TRPML1 and TRPML3 channels. This study will help a better understanding of TRPML2 and further investigation of its physiological functions.
Novel regulation of VGCCs
The activity of VGCCs is regulated by numerous signaling pathways and proteins, including phosphorylation/dephosphorylation, membrane lipids, G proteins and calmodulin (CaM). We have uncovered a novel regulation of VGCCs by proteolysis: the pore-forming 1 subunit of L- and P/Q-type VGCCs is cleaved by proteases in the middle of the protein, producing two or more channel fragments that dissociate and traffic to different subcellular compartments. This midchannel proteolysis is age dependent and is regulated by calcium and channel activity through negative-feedback mechanisms. We are studying the molecular and cellular mechanisms of midchannel proteolysis, its physiological importance, and its relevance to human diseases. The tools we use include biochemistry, electrophysiology, mouse genetics, and confocal and high-resolution microscopy. This work may lead to the discovery of new molecules and pathways that inform new means to modulate VGCC activities and new therapeutic strategies for VGCC channeopathies.
Structures of native brain VGCCs
To fully understand how VGCCs in the brain work, are regulated, and function physiologically, it is necessary to obtain high-resolution structures of native channels, alone and in complex with their regulatory proteins. We are developing methods to purify native VGCC complexes and will strive to determine their structures. Further work will be geared toward structure-based elucidation of the pathophysiological role of VGCCs in the brain.
Representative Publications (* indicates equal-contribution first authors; # indicates co-corresponding authors):
- Zheng, X.*, Li, H.*, Hu, Z.*, Su, D. and Yang, J. (2022). Structural and functional characterization of an achromatopsia-associated mutation in a phototransduction channel. Commun. Biol. 5, 190. https://doi.org/10.1038/s42003-022-03120-6
- Zheng, X., Hu, Z., Li, H., and Yang, J. (2022). Structure of the human cone photoreceptor cyclic nucleotide-gated channel. Nat. Struc. Mol. Biol. 29, 40-46.
- Jia, Q.*, Tian, W.*, Li, B.*, Chen, W.*, Zhang, W.*, Xie, Y., Cheng, N., Chen, Q., Xie, J.#, Zhang, Y.#, Yang, J.#, and Wang, S.# (2021) Transient Receptor Potential channels, TRPV1 and TRPA1 in melanocytes synergize UV-dependent and UV-independent melanogenesis. Br. J. Pharmacol. 178, 4646-4662.
- Zheng, X.*, Fu, Z.*, Su, D.*, Zhang Y., Li, M., Pan, Y., Li, H., Li, S., Grassucci, R.A., Ren, Z, Hu, Z., Li, X., Zhou, M., Li, G. #, Frank, J. #, and Yang, J. # (2020). Mechanism of ligand activation of a eukaryotic cyclic nucleotide-gated channel. Nat. Struc. Mol. Biol. 27, 625-634. (PMCID: PMC7354226)
- Zhou, X.*, Li, M-H.*, Su, D.*, Li, H., Jia, Q., Li, X.#, and Yang, J.# (2017). Cryo-EM structures of the human endolysosomal TRPML3 channel in three distinct states. Nat. Struc. Mol. Biol. 24, 1146-1154. (PMCID: PMC5747366)
- Wang, S.*#, Zhang, D.*, Hu, J.*, Xu, W.*, Su, D., Xu, Z., Cui, J., Zhou, M., Yang, J.#, and Xiao, J.# (2017). Clinical and mechanistic study of Bingpian, a topical analgesic in traditional Chinese medicine. EMBO Mol. Med. 9, 205-213. (PMCID: PMC5452010)
- Li, M-H.*, Zhang, W,K.*, Benvin, N*., Zhou, X., Su, D., Wang, S., Michailidis, I.E., Tong, L., Li, X., and Yang, J. (2017). Structural basis of Ca2+/pH dual regulation of the endolysosomal Ca2+ channel TRPML1. Nat. Struc. Mol. Biol. 24, 205-213. (PMCID: PMC5336481)
- Li, M.*, Zhou, X.*, Wang, S.*, Michailidis, I.E., Gong, Y., Su, D., Li, H., Li, X.#, and Yang, J.# (2017). Structure of a eukaryotic cyclic nucleotide-gated channel. Nature 542, 60-65. (PMCID: PMC5783306)
- Michailidis, I.E., Abele, K., Zhang, W.K., Lin, B., Yu, Y., Geyman, L., Ehlers, M.D., Pnevmatikakis, E.A., and Yang J. (2014). Age-related homeostatic midchannel proteolysis of L-type voltage-gated Ca2+ channels. Neuron 82, 1045-1057. (PMCID: PMC4052215)