9ZRQ: KCa2.2/calmodulin channel

Cryo-EM structure of KCa2.2/calmodulin channel in complex with SKA31. Determined by electron microscopy at 2.77 Å resolution. Released 14 Jan 2026.

Method: Electron microscopy
Resolution: 2.77 Å
Organism: Homo sapiens
Chains: 8
Atoms: 15,981
Mol. weight: 231.82 kDa
Ligands: A1C3Q, CA
Released: 14 Jan 2026

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

Secondary structure: helices and β-sheets

9ZRQ contains 87 α-helices and 24 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, 2 β-strands

Element	Residues	Length	Sheet
α-helix	121-156	36
α-helix	167-201	35
α-helix	212-225	14
β-strand	235-241	7	1
β-strand	248-254	7	1
α-helix	256-260	5
α-helix	261-268	8
α-helix	269-276	8
α-helix	284-292	9
α-helix	299-309	11
α-helix	311-334	24
α-helix	346-357	12
α-helix	370-397	28
α-helix	402-434	33
α-helix	446-477	32

Chain B: 14 helices, 2 β-strands

Element	Residues	Length	Sheet
α-helix	119-156	38
α-helix	167-200	34
α-helix	212-225	14
β-strand	235-241	7	2
β-strand	248-254	7	2
α-helix	256-260	5
α-helix	261-268	8
α-helix	269-276	8
α-helix	284-293	10
α-helix	299-309	11
α-helix	311-334	24
α-helix	346-357	12
α-helix	370-397	28
α-helix	400-401	2
α-helix	402-439	38
α-helix	446-477	32

Chain C: 13 helices, 2 β-strands

Element	Residues	Length	Sheet
α-helix	119-156	38
α-helix	167-200	34
α-helix	212-225	14
β-strand	235-241	7	3
β-strand	248-254	7	3
α-helix	256-260	5
α-helix	261-268	8
α-helix	269-276	8
α-helix	284-293	10
α-helix	299-309	11
α-helix	311-334	24
α-helix	346-357	12
α-helix	370-397	28
α-helix	402-438	37
α-helix	446-477	32

Chain D: 13 helices, 2 β-strands

Element	Residues	Length	Sheet
α-helix	119-156	38
α-helix	167-200	34
α-helix	212-225	14
β-strand	235-241	7	4
β-strand	248-254	7	4
α-helix	256-260	5
α-helix	261-268	8
α-helix	269-276	8
α-helix	284-290	7
α-helix	299-309	11
α-helix	311-334	24
α-helix	346-357	12
α-helix	370-397	28
α-helix	402-439	38
α-helix	446-477	32

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

Element	Residues	Length	Sheet
α-helix	6-17	12
β-strand	27	1	5
α-helix	31-38	8
α-helix	45-55	11
β-strand	63	1	5
α-helix	65-75	11
α-helix	81-91	11
β-strand	100-101	2	6
α-helix	102-111	10
α-helix	118-128	11
β-strand	135-136	2	6
α-helix	140-144	5

Chains F and H: 9 helices, 4 β-strands

Element	Residues	Length	Sheet
α-helix	6-17	12
β-strand	27	1	7
α-helix	29-38	10
α-helix	45-55	11
β-strand	63	1	7
α-helix	65-75	11
α-helix	81-92	12
β-strand	99-101	3	8
α-helix	102-107	6
α-helix	118-127	10
β-strand	135-137	3	8
α-helix	138-140	3
α-helix	142-145	4

Molecules and chains

Molecule	Chains	Type	Length	Organism	UniProt
Small conductance calcium-activated potassium channel protein 2	A, B, C, D	protein	361	Homo sapiens	Q9H2S1 (AlphaFold model)
Calmodulin-1	E, F, G, H	protein	146	Homo sapiens	P0DP23 (AlphaFold model)

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

>9ZRQ_1 Small conductance calcium-activated potassium channel protein 2 (chains A, B, C, D)
IGYKLGHRRALFEKRKRLSDYALIFGMFGIVVMVIETELSWGAYDKASLYSLALKCLISL
STIILLGLIIVYHAREIQLFMVDNGADDWRIAMTYERIFFICLEILVCAIHPIPGNYTFT
WTARLAFSYAPSTTTADVDIILSIPMFLRLYLIARVMLLHSKLFTDASSRSIGALNKINF
NTRFVMKTLMTICPGTVLLVFSISLWIIAAWTVRACERYHDQQDVTSNFLGAMWLISITF
LSIGYGDMVPNTYCGKGVCLLTGIMGAGCTALVVAVVARKLELTKAEKHVHNFMMDTQLT
KRVKNAAANVLRETWLIYKNTKLVKKIDHAKVRKHQRKFLQAIHQLRSVKMEQRKLNDQA
N

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

>9ZRQ_2 Calmodulin-1 (chains E, F, G, H)
DQLTEEQIAEFKEAFSLFDKDGDGTITTKELGTVMRSLGQNPTEAELQDMINEVDADGNG
TIDFPEFLTMMARKMKDTDSEEEIREAFRVFDKDGNGYISAAELRHVMTNLGEKLTDEEV
DEMIREADIDGDGQVNYEEFVQMMTA

Ligands and cofactors

ID	Name	Formula	Copies
A1C3Q	naphtho[1,2-d][1,3]thiazol-2-amine	C11 H8 N2 S	4
CA	Calcium ion	Ca	8

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

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 Q9H2S1 (AlphaFold model), which also has an AlphaFold model), best resolution first:

5V03 1.58 Å, A positive allosteric modulator binding pocket in SK2 ion channels is shared by Riluzole…
5V02 1.78 Å, A positive allosteric modulator binding pocket in SK2 ion channels is shared by Riluzole…
5WBX 1.9 Å, Structural insights into the potency of SK/IK channel positive modulators
5WC5 2.3 Å, Structural insights into the potency of SK/IK channel positive modulators
6ALE 2.5 Å, A V-to-F substitution in SK2 channels causes Ca2+ hypersensitivity and improves…
9VUC 2.96 Å, channel B complex with 2
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…
9VUA 3.23 Å, channel A complex with 1
9O53 3.3 Å, Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex bound to a small…
9ZRR 3.31 Å, Cryo-EM structure of KCa2.2/calmodulin channel in complex with SKA111.

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