9ZPO: KCa3.1_I/calmodulin channel
Cryo-EM structure of KCa3.1_I/calmodulin channel in complex with SKA31. Determined by electron microscopy at 3.67 Å resolution. Released 14 Jan 2026.
- Method
- Electron microscopy
- Resolution
- 3.67 Å
- Organism
- Homo sapiens
- Chains
- 8
- Atoms
- 13,966
- Mol. weight
- 217.21 kDa
- Ligands
- CA, A1C3Q
- Released
- 14 Jan 2026
Explore 9ZPO in 3D
Show helices and sheets
RCSB PDB
PDBe
Secondary structure: helices and β-sheets
9ZPO contains 92 α-helices and 20 β-strands across 8 chains. Residue ranges use author residue numbering, as in the PDB file, from PDBe. To see them in 3D, choose the Cartoon representation with Secondary structure coloring: helices, sheets and coils get different colors.
Chain A: 13 helices, 0 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 14-33 | 20 | |
| α-helix | 35-46 | 12 | |
| α-helix | 57-59 | 3 | |
| α-helix | 61-91 | 31 | |
| α-helix | 102-115 | 14 | |
| α-helix | 162-170 | 9 | |
| α-helix | 182-185 | 4 | |
| α-helix | 192-202 | 11 | |
| α-helix | 206-225 | 20 | |
| α-helix | 262-288 | 27 | |
| α-helix | 293-330 | 38 | |
| α-helix | 334-365 | 32 | |
| α-helix | 375-383 | 9 | |
Chain B: 15 helices, 0 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 14-33 | 20 | |
| α-helix | 35-46 | 12 | |
| α-helix | 57-91 | 35 | |
| α-helix | 102-115 | 14 | |
| α-helix | 155-158 | 4 | |
| α-helix | 162-170 | 9 | |
| α-helix | 182-185 | 4 | |
| α-helix | 192-202 | 11 | |
| α-helix | 206-226 | 21 | |
| α-helix | 261-288 | 28 | |
| α-helix | 296-330 | 35 | |
| α-helix | 334-363 | 30 | |
| α-helix | 364-368 | 5 | |
| α-helix | 370-373 | 4 | |
| α-helix | 375-383 | 9 | |
Chain C: 15 helices, 0 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 14-33 | 20 | |
| α-helix | 35-47 | 13 | |
| α-helix | 57-91 | 35 | |
| α-helix | 96-98 | 3 | |
| α-helix | 102-115 | 14 | |
| α-helix | 162-169 | 8 | |
| α-helix | 182-185 | 4 | |
| α-helix | 192-202 | 11 | |
| α-helix | 206-225 | 20 | |
| α-helix | 262-288 | 27 | |
| α-helix | 296-330 | 35 | |
| α-helix | 334-363 | 30 | |
| α-helix | 364-368 | 5 | |
| α-helix | 370-373 | 4 | |
| α-helix | 375-383 | 9 | |
Chain D: 13 helices, 0 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 14-33 | 20 | |
| α-helix | 35-47 | 13 | |
| α-helix | 57-90 | 34 | |
| α-helix | 102-116 | 15 | |
| α-helix | 154-156 | 3 | |
| α-helix | 162-170 | 9 | |
| α-helix | 177-180 | 4 | |
| α-helix | 192-202 | 11 | |
| α-helix | 206-225 | 20 | |
| α-helix | 262-288 | 27 | |
| α-helix | 296-330 | 35 | |
| α-helix | 336-365 | 30 | |
| α-helix | 375-383 | 9 | |
Chain E: 9 helices, 6 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 6-19 | 14 | |
| β-strand | 27 | 1 | 1 |
| α-helix | 29-38 | 10 | |
| α-helix | 45-55 | 11 | |
| β-strand | 63 | 1 | 1 |
| α-helix | 65-75 | 11 | |
| α-helix | 81-84 | 4 | |
| α-helix | 87-90 | 4 | |
| β-strand | 100 | 1 | 2 |
| α-helix | 102-106 | 5 | |
| β-strand | 112 | 1 | 3 |
| β-strand | 114 | 1 | 3 |
| α-helix | 118-128 | 11 | |
| β-strand | 136 | 1 | 2 |
| α-helix | 138-146 | 9 | |
Chain F: 9 helices, 4 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 6-17 | 12 | |
| β-strand | 27 | 1 | 4 |
| α-helix | 29-39 | 11 | |
| α-helix | 45-55 | 11 | |
| β-strand | 63 | 1 | 4 |
| α-helix | 66-75 | 10 | |
| α-helix | 81-84 | 4 | |
| α-helix | 87-92 | 6 | |
| β-strand | 100 | 1 | 5 |
| α-helix | 102-106 | 5 | |
| α-helix | 118-128 | 11 | |
| β-strand | 136 | 1 | 5 |
| α-helix | 138-146 | 9 | |
Chain G: 10 helices, 4 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 6-19 | 14 | |
| β-strand | 27 | 1 | 6 |
| α-helix | 29-38 | 10 | |
| α-helix | 45-55 | 11 | |
| β-strand | 63 | 1 | 6 |
| α-helix | 65-75 | 11 | |
| α-helix | 81-84 | 4 | |
| α-helix | 87-90 | 4 | |
| α-helix | 91-93 | 3 | |
| β-strand | 100 | 1 | 7 |
| α-helix | 102-108 | 7 | |
| α-helix | 118-128 | 11 | |
| β-strand | 136 | 1 | 7 |
| α-helix | 138-146 | 9 | |
Chain H: 8 helices, 6 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 6-17 | 12 | |
| β-strand | 27 | 1 | 8 |
| α-helix | 29-38 | 10 | |
| α-helix | 45-55 | 11 | |
| β-strand | 63 | 1 | 8 |
| α-helix | 65-75 | 11 | |
| α-helix | 81-91 | 11 | |
| β-strand | 100 | 1 | 9 |
| α-helix | 102-108 | 7 | |
| β-strand | 112 | 1 | 10 |
| β-strand | 114 | 1 | 10 |
| α-helix | 118-128 | 11 | |
| β-strand | 136 | 1 | 9 |
| α-helix | 138-146 | 9 | |
Molecules and chains
| Molecule | Chains | Type | Length | Organism | UniProt |
|---|
| Intermediate conductance calcium-activated potassium channel protein 4 | A, B, C, D | protein | 329 | Homo sapiens | O15554 (AlphaFold model) |
| Calmodulin-1 | E, F, G, H | protein | 146 | Homo sapiens | P0DP23 (AlphaFold model) |
Sequence of entity 1 (A, B, C, D), FASTA
>9ZPO_1 Intermediate conductance calcium-activated potassium channel protein 4 (chains A, B, C, D)
LGALRRRKRLLEQEKSLAGWALVLAGTGIGLMVLHAEMLWFGGCSWALYLFLVKCTISIS
TFLLLCLIVAFHAKEVQLFMTDNGLRDWRVALTGRQAAQIVLELVVCGLHPAPVRPGFLG
QGEALLSLAMLLRLYLVPRAVLLRSGVLLNASYRSIGALNQVRFRHWFVAKLYMNTHPGR
LLLGLTLGLWLTTAWVLSVAERTMWGKIVCLCTGVMGVCCTALLVAVVARKLEFNKAEKH
VHNFMMDIQYTKEMKESAARVLQEAWMFYKHTRRKESHAARRHQRKLLAAINAFRQVRLK
HRKLREQVNSMVDISKMHMILYDLQQNLS
Sequence of entity 2 (E, F, G, H), FASTA
>9ZPO_2 Calmodulin-1 (chains E, F, G, H)
DQLTEEQIAEFKEAFSLFDKDGDGTITTKELGTVMRSLGQNPTEAELQDMINEVDADGNG
TIDFPEFLTMMARKMKDTDSEEEIREAFRVFDKDGNGYISAAELRHVMTNLGEKLTDEEV
DEMIREADIDGDGQVNYEEFVQMMTA
Ligands and cofactors
| ID | Name | Formula | Copies |
|---|
| CA | Calcium ion | Ca | 8 |
| A1C3Q | naphtho[1,2-d][1,3]thiazol-2-amine | C11 H8 N2 S | 4 |
Primary citation
Structural basis for the subtype-selective activation of K Ca 3.1 channels. Ramanishka, A., Nasburg, J.A., Xu, Y. et al. Structure (2026) 34:1040-1049.e3. DOI 10.1016/j.str.2026.04.010 · PubMed
Other PDB entries of the same protein (UniProt O15554 (AlphaFold model), which also has an AlphaFold model), best resolution first:
- 6D42 1.75 Å, Crystal structure of the KCa3.1 C-terminal four-helix bundle (with copper)
- 9ZRK 2.99 Å, Cryo-EM structure of KCa3.1_I/calmodulin channel in complex with SKA111.
- 9O48 3.1 Å, Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex in the Ca2+…
- 9O5O 3.1 Å, Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex bound to a small…
- 9O52 3.18 Å, Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex bound to the bee…
- 9O53 3.3 Å, Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex bound to a small…
- 9ZRL 3.38 Å, Cryo-EM structure of KCa3.1_II/calmodulin channel in complex with SKA111.
- 9ZPT 3.39 Å, Cryo-EM structure of KCa3.1_II/calmodulin channel in complex with SKA31.
- 6CNM 3.4 Å, Cryo-EM structure of the human SK4/calmodulin channel complex
- 9O51 3.4 Å, Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex in the Ca2+ free…
- 9YDZ 3.4 Å, Cryo EM structure of KCa3.1_R355K_II/calmodulin channel in complex with rimtuzalcap
- 6CNN 3.5 Å, Cryo-EM structure of the human SK4/calmodulin channel complex in the Ca2+ bound state I
Browse structure collections
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