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- PDB-9ydz: Cryo EM structure of KCa3.1_R355K_II/calmodulin channel in comple... -

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Basic information

Entry
Database: PDB / ID: 9ydz
TitleCryo EM structure of KCa3.1_R355K_II/calmodulin channel in complex with rimtuzalcap
Components
  • Calmodulin-1
  • Intermediate conductance calcium-activated potassium channel protein 4
KeywordsTRANSPORT PROTEIN / Ion channel / Intermediate conductance calcium-activated potassium channel / Calmodulin binding protein
Function / homology
Function and homology information


intermediate conductance calcium-activated potassium channel activity / saliva secretion / Ca2+ activated K+ channels / small conductance calcium-activated potassium channel activity / stabilization of membrane potential / macropinocytosis / calcium-activated potassium channel activity / regulation of calcium ion import across plasma membrane / positive regulation of potassium ion transmembrane transport / cell volume homeostasis ...intermediate conductance calcium-activated potassium channel activity / saliva secretion / Ca2+ activated K+ channels / small conductance calcium-activated potassium channel activity / stabilization of membrane potential / macropinocytosis / calcium-activated potassium channel activity / regulation of calcium ion import across plasma membrane / positive regulation of potassium ion transmembrane transport / cell volume homeostasis / CaM pathway / Cam-PDE 1 activation / Sodium/Calcium exchangers / Calmodulin induced events / Reduction of cytosolic Ca++ levels / phospholipid translocation / Activation of Ca-permeable Kainate Receptor / CREB1 phosphorylation through the activation of CaMKII/CaMKK/CaMKIV cascasde / Loss of phosphorylation of MECP2 at T308 / CREB1 phosphorylation through the activation of Adenylate Cyclase / negative regulation of high voltage-gated calcium channel activity / PKA activation / CaMK IV-mediated phosphorylation of CREB / Glycogen breakdown (glycogenolysis) / CLEC7A (Dectin-1) induces NFAT activation / Activation of RAC1 downstream of NMDARs / negative regulation of ryanodine-sensitive calcium-release channel activity / organelle localization by membrane tethering / mitochondrion-endoplasmic reticulum membrane tethering / autophagosome membrane docking / negative regulation of calcium ion export across plasma membrane / regulation of cardiac muscle cell action potential / presynaptic endocytosis / Synthesis of IP3 and IP4 in the cytosol / regulation of cell communication by electrical coupling involved in cardiac conduction / Phase 0 - rapid depolarisation / calcineurin-mediated signaling / Negative regulation of NMDA receptor-mediated neuronal transmission / Unblocking of NMDA receptors, glutamate binding and activation / positive regulation of T cell receptor signaling pathway / RHO GTPases activate PAKs / Ion transport by P-type ATPases / Uptake and function of anthrax toxins / regulation of ryanodine-sensitive calcium-release channel activity / Long-term potentiation / protein phosphatase activator activity / Calcineurin activates NFAT / Regulation of MECP2 expression and activity / DARPP-32 events / Smooth Muscle Contraction / immune system process / detection of calcium ion / potassium channel activity / regulation of cardiac muscle contraction / catalytic complex / RHO GTPases activate IQGAPs / regulation of cardiac muscle contraction by regulation of the release of sequestered calcium ion / calcium channel inhibitor activity / Activation of AMPK downstream of NMDARs / cellular response to interferon-beta / presynaptic cytosol / Protein methylation / regulation of release of sequestered calcium ion into cytosol by sarcoplasmic reticulum / eNOS activation / titin binding / Ion homeostasis / Tetrahydrobiopterin (BH4) synthesis, recycling, salvage and regulation / regulation of calcium-mediated signaling / sperm midpiece / voltage-gated potassium channel complex / potassium ion transmembrane transport / FCERI mediated Ca+2 mobilization / calcium channel complex / substantia nigra development / regulation of heart rate / Ras activation upon Ca2+ influx through NMDA receptor / FCGR3A-mediated IL10 synthesis / Antigen activates B Cell Receptor (BCR) leading to generation of second messengers / calyx of Held / adenylate cyclase activator activity / sarcomere / protein serine/threonine kinase activator activity / VEGFR2 mediated cell proliferation / VEGFR2 mediated vascular permeability / regulation of cytokinesis / positive regulation of protein secretion / spindle microtubule / positive regulation of receptor signaling pathway via JAK-STAT / Translocation of SLC2A4 (GLUT4) to the plasma membrane / calcium channel regulator activity / establishment of localization in cell / RAF activation / defense response / Transcriptional activation of mitochondrial biogenesis / response to calcium ion / potassium ion transport / cellular response to type II interferon / G2/M transition of mitotic cell cycle / Stimuli-sensing channels / ruffle membrane
Similarity search - Function
Calmodulin-binding domain / Potassium channel, calcium-activated, SK / SK, calmodulin-binding domain superfamily / Calmodulin binding domain / Calcium-activated SK potassium channel / Calmodulin binding domain / Potassium channel domain / Ion channel / : / EF-hand domain pair ...Calmodulin-binding domain / Potassium channel, calcium-activated, SK / SK, calmodulin-binding domain superfamily / Calmodulin binding domain / Calcium-activated SK potassium channel / Calmodulin binding domain / Potassium channel domain / Ion channel / : / EF-hand domain pair / EF-hand, calcium binding motif / EF-Hand 1, calcium-binding site / EF-hand calcium-binding domain. / EF-hand calcium-binding domain profile. / EF-hand domain / EF-hand domain pair
Similarity search - Domain/homology
: / Intermediate conductance calcium-activated potassium channel protein 4 / Calmodulin-1
Similarity search - Component
Biological speciesHomo sapiens (human)
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 3.4 Å
AuthorsNam, Y.W. / Zhang, M.
Funding support United States, 4items
OrganizationGrant numberCountry
American Heart Association23AIREA1039423 United States
American Heart Association24CDA1260237 United States
National Institutes of Health/National Institute of Neurological Disorders and Stroke (NIH/NINDS)4R33 NS101182-03 United States
National Institutes of Health/National Institute of Neurological Disorders and Stroke (NIH/NINDS)R15 NS130420-01A1 United States
CitationJournal: Nat Commun / Year: 2026
Title: Structural basis for the subtype-selectivity of K2.2 channel activators.
Authors: Young-Woo Nam / Alena Ramanishka / Yang Xu / Rose Marie Haynes Yasuda / Joshua A Nasburg / Dohyun Im / Meng Cui / K George Chandy / Heike Wulff / Miao Zhang /
Abstract: Small-conductance (K2.2) and intermediate-conductance (K3.1) Ca-activated K channels are gated by a Ca-calmodulin dependent mechanism. NS309 potentiates the activity of both K2.2 and K3.1, while ...Small-conductance (K2.2) and intermediate-conductance (K3.1) Ca-activated K channels are gated by a Ca-calmodulin dependent mechanism. NS309 potentiates the activity of both K2.2 and K3.1, while rimtuzalcap selectively activates K2.2. Rimtuzalcap has been used in clinical trials for the treatment of spinocerebellar ataxia and essential tremor. We report cryo-electron microscopy structures of NS309-bound K2.2 and K3.1, in addition to structures of rimtuzalcap-bound K2.2 and mutant K3.1_R355K. The different conformations of calmodulin and the cytoplasmic HC helices in the two channels underlie the subtype-selectivity of rimtuzalcap for K2.2. NS309 binds to pre-existing pockets in both channels, while the bulkier rimtuzalcap binds in an induced-fit pocket in K2.2 requiring conformational changes. In K2.2, calmodulin's N-lobes are sufficiently far apart to enable conformational changes to accommodate either NS309 or rimtuzalcap. In K3.1, calmodulin's N-lobes are closer to each other and constrained by K3.1's HC helices, which allows binding of NS309 but not rimtuzalcap. Replacement of arginine-355 in K3.1's HB helix with lysine (K3.1_R355K) allows the binding of rimtuzalcap and renders the mutant channel sensitive to rimtuzalcap. These structures provide a framework for structure-based drug design targeting K2.2 channels.
History
DepositionSep 23, 2025Deposition site: RCSB / Processing site: RCSB
Revision 1.0Oct 1, 2025Provider: repository / Type: Initial release
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Structure visualization

Structure viewerMolecule:
MolmilJmol/JSmol

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Assembly

Deposited unit
A: Intermediate conductance calcium-activated potassium channel protein 4
B: Intermediate conductance calcium-activated potassium channel protein 4
C: Intermediate conductance calcium-activated potassium channel protein 4
D: Intermediate conductance calcium-activated potassium channel protein 4
E: Calmodulin-1
F: Calmodulin-1
G: Calmodulin-1
H: Calmodulin-1
hetero molecules


Theoretical massNumber of molelcules
Total (without water)191,81712
Polymers191,6618
Non-polymers1564
Water00
1


  • Idetical with deposited unit
  • defined by author
  • Evidence: electron microscopy, not applicable
TypeNameSymmetry operationNumber
identity operation1_5551

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Components

#1: Protein
Intermediate conductance calcium-activated potassium channel protein 4 / SKCa 4 / SKCa4 / hSK4 / Gardos channel / IKCa1 / hIK1 / KCa3.1 / Putative Gardos channel / hKCa4


Mass: 40219.852 Da / Num. of mol.: 4 / Mutation: R355K
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Homo sapiens (human) / Gene: KCNN4, IK1, IKCA1, KCA4, SK4 / Production host: Homo sapiens (human) / References: UniProt: O15554
#2: Protein
Calmodulin-1


Mass: 7695.366 Da / Num. of mol.: 4 / Fragment: residues 82-148
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Homo sapiens (human) / Gene: CALM1, CALM, CAM, CAM1 / Production host: Homo sapiens (human) / References: UniProt: P0DP23
#3: Chemical
ChemComp-K / POTASSIUM ION


Mass: 39.098 Da / Num. of mol.: 4 / Source method: obtained synthetically / Formula: K
Has ligand of interestN
Has protein modificationN

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Experimental details

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Experiment

ExperimentMethod: ELECTRON MICROSCOPY
EM experimentAggregation state: PARTICLE / 3D reconstruction method: single particle reconstruction

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Sample preparation

ComponentName: Human KCa3.1_R355K_II/calmodulin channel in complex with rimtuzalcap
Type: COMPLEX / Entity ID: #1-#2 / Source: RECOMBINANT
Molecular weightValue: 0.23166 MDa / Experimental value: NO
Source (natural)Organism: Homo sapiens (human)
Source (recombinant)Organism: Homo sapiens (human) / Strain: HEK293s / Cell: HEK293 / Plasmid: pGEBacMam
Buffer solutionpH: 8
SpecimenConc.: 2 mg/ml / Embedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES
VitrificationCryogen name: ETHANE

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Electron microscopy imaging

Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company
MicroscopyModel: TFS KRIOS
Electron gunElectron source: FIELD EMISSION GUN / Accelerating voltage: 300 kV / Illumination mode: FLOOD BEAM
Electron lensMode: BRIGHT FIELD / Nominal defocus max: 2200 nm / Nominal defocus min: 600 nm
Specimen holderSpecimen holder model: FEI TITAN KRIOS AUTOGRID HOLDER
Image recordingElectron dose: 50 e/Å2 / Film or detector model: FEI FALCON IV (4k x 4k)

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Processing

EM software
IDNameVersionCategory
1cryoSPARCparticle selection
7Coot0.9.8.95 ELmodel fitting
9PHENIX1.21.1_5286model refinement
13cryoSPARC3D reconstruction
CTF correctionType: PHASE FLIPPING AND AMPLITUDE CORRECTION
3D reconstructionResolution: 3.4 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 80295 / Symmetry type: POINT
RefinementHighest resolution: 3.4 Å
Stereochemistry target values: REAL-SPACE (WEIGHTED MAP SUM AT ATOM CENTERS)
Refine LS restraints
Refine-IDTypeDev idealNumber
ELECTRON MICROSCOPYf_bond_d0.00212451
ELECTRON MICROSCOPYf_angle_d0.46216889
ELECTRON MICROSCOPYf_dihedral_angle_d3.5891746
ELECTRON MICROSCOPYf_chiral_restr0.0351989
ELECTRON MICROSCOPYf_plane_restr0.0022101

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