9OA8: KCa3.1/calmodulin channel

Cryo-EM structure of KCa3.1/calmodulin channel in complex with NS309. Determined by electron microscopy at 3.59 Å resolution. Released 18 Jun 2025.

Method: Electron microscopy
Resolution: 3.59 Å
Organisms: Homo sapiens, Rattus norvegicus
Chains: 8
Atoms: 15,255
Mol. weight: 237.84 kDa
Ligands: CA, 1KP
Released: 18 Jun 2025

Explore 9OA8 in 3D Show helices and sheets RCSB PDB PDBe

Secondary structure: helices and β-sheets

9OA8 contains 99 α-helices and 16 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: 17 helices, 0 β-strands

Element	Residues	Length
α-helix	11-28	18
α-helix	31-48	18
α-helix	57-70	14
α-helix	72-91	20
α-helix	102-114	13
α-helix	150-154	5
α-helix	155-161	7
α-helix	162-171	10
α-helix	182-185	4
α-helix	192-202	11
α-helix	204-215	12
α-helix	222-225	4
α-helix	237-248	12
α-helix	266-288	23
α-helix	296-329	34
α-helix	336-367	32
α-helix	372-385	14

Chain B: 16 helices, 0 β-strands

Element	Residues	Length
α-helix	11-49	39
α-helix	56-80	25
α-helix	83-91	9
α-helix	96-99	4
α-helix	102-114	13
α-helix	147-154	8
α-helix	155-161	7
α-helix	162-168	7
α-helix	179-184	6
α-helix	192-202	11
α-helix	204-226	23
α-helix	237-248	12
α-helix	266-287	22
α-helix	296-330	35
α-helix	335-368	34
α-helix	371-385	15

Chain C: 16 helices, 0 β-strands

Element	Residues	Length
α-helix	10-27	18
α-helix	31-48	18
α-helix	61-91	31
α-helix	102-114	13
α-helix	150-154	5
α-helix	155-161	7
α-helix	162-167	6
α-helix	179-184	6
α-helix	192-202	11
α-helix	204-218	15
α-helix	222-226	5
α-helix	237-248	12
α-helix	261-288	28
α-helix	296-327	32
α-helix	335-366	32
α-helix	371-385	15

Chain D: 18 helices, 0 β-strands

Element	Residues	Length
α-helix	10-25	16
α-helix	28-49	22
α-helix	55-67	13
α-helix	72-91	20
α-helix	96-99	4
α-helix	104-114	11
α-helix	147-154	8
α-helix	155-161	7
α-helix	162-168	7
α-helix	179-184	6
α-helix	192-202	11
α-helix	204-226	23
α-helix	237-248	12
α-helix	261-288	28
α-helix	291-292	2
α-helix	296-330	35
α-helix	335-366	32
α-helix	373-385	13

Chains E, F, G and H: 8 helices, 4 β-strands

Element	Residues	Length	Sheet
α-helix	6-19	14
β-strand	27	1	1
α-helix	29-39	11
α-helix	45-53	9
β-strand	63	1	1
α-helix	65-75	11
α-helix	83-90	8
β-strand	100	1	2
α-helix	102-109	8
α-helix	118-128	11
β-strand	136	1	2
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	378	Homo sapiens	O15554 (AlphaFold model)
Calmodulin-1	E, F, G, H	protein	146	Rattus norvegicus	P0DP29 (AlphaFold model)

Sequence of entity 1 (A, B, C, D), FASTA

>9OA8_1 Intermediate conductance calcium-activated potassium channel protein 4 (chains A, B, C, D)
LGALRRRKRLLEQEKSLAGWALVLAGTGIGLMVLHAEMLWFGGCSWALYLFLVKCTISIS
TFLLLCLIVAFHAKEVQLFMTDNGLRDWRVALTGRQAAQIVLELVVCGLHPAPVRGPPCV
QDLGAPLTSPQPWPGFLGQGEALLSLAMLLRLYLVPRAVLLRSGVLLNASYRSIGALNQV
RFRHWFVAKLYMNTHPGRLLLGLTLGLWLTTAWVLSVAERQAVNATGHLSDTLWLIPITF
LTIGYGDVVPGTMWGKIVCLCTGVMGVCCTALLVAVVARKLEFNKAEKHVHNFMMDIQYT
KEMKESAARVLQEAWMFYKHTRRKESHAARRHQRKLLAAINAFRQVRLKHRKLREQVNSM
VDISKMHMILYDLQQNLS

Sequence of entity 2 (E, F, G, H), FASTA

>9OA8_2 Calmodulin-1 (chains E, F, G, H)
DQLTEEQIAEFKEAFSLFDKDGDGTITTKELGTVMRSLGQNPTEAELQDMINEVDADGNG
TIDFPEFLTMMARKMKDTDSEEEIREAFRVFDKDGNGYISAAELRHVMTNLGEKLTDEEV
DEMIREADIDGDGQVNYEEFVQMMTA

Ligands and cofactors

ID	Name	Formula	Copies
CA	Calcium ion	Ca	8
1KP	(3E)-6,7-dichloro-3-(hydroxyimino)-1,3-dihydro-2H-indol-2-one	C8 H4 Cl2 N2 O2	4

Water and common crystallization additives (K) are not listed.

Primary citation

Structural basis for the subtype-selectivity of K Ca 2.2 channel activators. Nam, Y.W., Ramanishka, A., Xu, Y. et al. Nat Commun (2026) 17:531-531. DOI 10.1038/s41467-025-67232-3 · 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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