Cryo-EM structures of the small-conductance Ca2+-activated KCa2.2 channel
Small-conductance Ca<sup>2+</sup>-activated K<sup>+</sup> (K<sub>Ca</sub>2.1-K<sub>Ca</sub>2.3) channels modulate neuronal and cardiac excitability. We report cryo-electron microscopy structures of the K<sub>Ca</sub>2.2 channel in complex with calmodulin and Ca<sup>2+</sup>, alone or bound to two small molecule inhibitors, at 3.18, 3.50, 2.99 and 2.97 angstrom resolution, respectively. Extracellular S3-S4 loops in β-hairpin configuration form an outer canopy over the pore with an aromatic box at the canopy's center. Each S3-S4 β-hairpin is tethered to the selectivity filter in the neighboring subunit by inter-subunit hydrogen bonds. This hydrogen bond network flips the aromatic residue (Tyr362) in the filter's GYG signature by 180°, causing the outer selectivity filter to widen and water to enter the filter. Disruption of the tether by a mutation narrows the outer selectivity filter, realigns Tyr362 to the position seen in other K<sup>+</sup> channels, and significantly increases unitary conductance. UCL1684, a mimetic of the bee venom peptide apamin, sits atop the canopy and occludes the opening in the aromatic box. AP14145, an analogue of a therapeutic for atrial fibrillation, binds in the central cavity below the selectivity filter and induces closure of the inner gate. These structures provide a basis for understanding the small unitary conductance and pharmacology of K<sub>Ca</sub>2.x channels.
Authors
- Hai M. Nguyen (ORCID: https://orcid.org/0000-0002-1422-7041)
- Young-Woo Nam (ORCID: https://orcid.org/0000-0003-2960-9752)
- Razan Orfali (ORCID: https://orcid.org/0000-0002-0584-4013)
- Grigore Pintilie (ORCID: https://orcid.org/0000-0002-0848-5335)
- Marios Tringides (ORCID: https://orcid.org/0000-0002-3800-2365)
- Diomedes E. Logothetis (ORCID: https://orcid.org/0000-0002-0576-884X)
- Adriana Garcia
- Heike Wulff (ORCID: https://orcid.org/0000-0003-4437-5763)
- Dohyun Im (ORCID: https://orcid.org/0000-0002-6939-7718)
- K. George Chandy (ORCID: https://orcid.org/0000-0002-5237-8756)
- Chih‐Chia Su (ORCID: https://orcid.org/0000-0003-3646-327X)
- Meng Cui (ORCID: https://orcid.org/0000-0002-3895-135X)
- Yan Liu (ORCID: https://orcid.org/0000-0001-5683-8695)
- Miao Zhang (ORCID: https://orcid.org/0000-0002-3099-155X)
- Eunsun Yu (ORCID: https://orcid.org/0000-0001-5912-1227)
- Alena Ramanishka
Institutions
- Northeastern University (US)
- Nanyang Technological University (SG)
- Chapman University (US)
- Kyoto University (JP)
- SLAC National Accelerator Laboratory (US)
- Stanford Synchrotron Radiation Lightsource (US)
- University School (US)
- Case Western Reserve University (US)
- University of California, Davis (US)
- Stanford University (US)
Publication Details
- Journal
- Nature Communications
- Published
- 2025-04-17
- DOI
- https://doi.org/10.1038/s41467-025-59061-1
- Citations
- 13
- Primary Topic
- Ion channel regulation and function
- Type
- article
- Field-Weighted Citation Impact
- 10.48
Funders
- American Heart Association
- National Ataxia Foundation
- Chapman University
- National Institutes of Health
- National Institute of Neurological Disorders and Stroke
- Argonne National Laboratory
- SLAC National Accelerator Laboratory
- Common Fund