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Protein Structures and Oligomeric States

Enter a protein name, UniProt accession or PDB ID. Name searches ask you to confirm the protein identity before related structures are queried.

Current Protein Identity：O15554 New Search
17PDB entries
18Biological assembly
86chain/assembly records
Main Difference Dimensions in This Set
Different construct Different mutation/modification Different assembly state Different ligand/ion Different experimental method Different experimental conditions Different structure-quality metrics

Difference tags compare only the current result set; every original PDB and assembly record remains separate.

Related-Structure Differences

Each row represents one biological assembly in one PDB entry; multiple monomers of the same protein are listed separately.

PDB Entry Assembly / Oligomeric State Construct Mutations and Modifications Ligands, Ions and Non-polymers Experimental Method Experimental Conditions Structure Quality
6CNM Cryo-EM structure of the human SK4/calmodulin channel complex Deposited 2018-03-08 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 1–427（427 aa）
Chain B 1–427（427 aa）
Chain C 1–427（427 aa）
Chain D 1–427（427 aa）
Not recorded K POTASSIUM ION × 5 POV (2S)-3-(hexadecanoyloxy)-2-[(9Z)-octadec-9-enoyloxy]propyl 2-(trimethylammonio)ethyl phosphate × 4 LMT DODECYL-BETA-D-MALTOSIDE × 8 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 3.40 Å
6CNN Cryo-EM structure of the human SK4/calmodulin channel complex in the Ca2+ bound state I Deposited 2018-03-08 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 1–427（427 aa）
Chain B 1–427（427 aa）
Chain C 1–427（427 aa）
Chain D 1–427（427 aa）
Not recorded K POTASSIUM ION × 4 POV (2S)-3-(hexadecanoyloxy)-2-[(9Z)-octadec-9-enoyloxy]propyl 2-(trimethylammonio)ethyl phosphate × 4 LMT DODECYL-BETA-D-MALTOSIDE × 8 CA CALCIUM ION × 12 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 3.50 Å
6CNO Cryo-EM structure of the human SK4/calmodulin channel complex in the Ca2+ bound state II Deposited 2018-03-08 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 1–427（427 aa）
Chain B 1–427（427 aa）
Chain C 1–427（427 aa）
Chain D 1–427（427 aa）
Not recorded CA CALCIUM ION × 12 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 4.70 Å
6D42 Crystal structure of the KCa3.1 C-terminal four-helix bundle (with copper) Deposited 2018-04-17 Assembly 1 Protein homooligomer Homooligomer；Protein × 4 PDB declaration: tetrameric（4） Consistent with protein count
Chain A 376–415（40 aa）
Non-standard monomer：Yes (specific site not provided by mmCIF) CU COPPER (II) ION × 4 X-RAY DIFFRACTION
X-ray crystallization conditions VAPOR DIFFUSION, HANGING DROP；pH 6.5；290 K；0.1 M imidazole, pH 6.5 1.0 M sodium acetate
Resolution 1.75 Å R-free 0.323
6D42 Crystal structure of the KCa3.1 C-terminal four-helix bundle (with copper) Deposited 2018-04-17 Assembly 2 Protein homooligomer Homooligomer；Protein × 4 PDB declaration: tetrameric（4） Consistent with protein count
Chain B 376–415（40 aa）
Non-standard monomer：Yes (specific site not provided by mmCIF) CU COPPER (II) ION × 4 X-RAY DIFFRACTION
X-ray crystallization conditions VAPOR DIFFUSION, HANGING DROP；pH 6.5；290 K；0.1 M imidazole, pH 6.5 1.0 M sodium acetate
Resolution 1.75 Å R-free 0.323
9ED1 Cryo-EM structure of the human KCa3.1/calmodulin channel in complex with Ca2+ and 1,4-dihydropyridine (DHP-103) Deposited 2024-11-15 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 9–386（378 aa）
Chain B 9–386（378 aa）
Chain C 9–386（378 aa）
Chain D 9–386（378 aa）
Not recorded K POTASSIUM ION × 5 CA CALCIUM ION × 12 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 3.50 Å
9O48 Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex in the Ca2+ bound state Deposited 2025-04-08 Assembly 1 Insufficient information Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain A 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Not recorded K POTASSIUM ION × 2 CA CALCIUM ION × 16 ELECTRON MICROSCOPY
cryo-EM buffer pH 8；20 mM Tris pH 8, 150 mM KCl, 2 mM CaCl2, 0.005% GDN, 0.0005% CHS
cryo-EM vitrification conditions Cryogen ETHANE；5 uL of sample was applied to grids at 4 degree temperature with 100% humidity. After 30 seconds, grids were blotted for 5 seconds with blot force 25 and plunged into liquid ethane.
Resolution 3.10 Å
9O51 Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex in the Ca2+ free state Deposited 2025-04-09 Assembly 1 Insufficient information Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain A 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Not recorded K POTASSIUM ION × 2 CA CALCIUM ION × 4 ELECTRON MICROSCOPY
cryo-EM buffer pH 8；20 mM Tris pH 8, 150 mM KCl, 5 mM EGTA, 0.005% GDN, 0.0005% CHS
cryo-EM vitrification conditions Cryogen ETHANE；5 uL of sample was applied to grids at 4 degree temperature with 100% humidity. After 30 seconds, grids were blotted for 5 seconds with blot force 25 and plunged into liquid ethane.
Resolution 3.40 Å
9O52 Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex bound to the bee toxin apamin Deposited 2025-04-09 Assembly 1 Insufficient information Heteromer；Protein × 9 PDB declaration: nonameric（9） Consistent with protein count
Chain A 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain A 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Not recorded K POTASSIUM ION × 4 CA CALCIUM ION × 16 ELECTRON MICROSCOPY
cryo-EM buffer pH 8；20 mM Tris pH 8, 150 mM KCl, 2 mM CaCl2, 0.005% GDN, 0.0005% CHS
cryo-EM vitrification conditions Cryogen ETHANE；5 uL of sample was applied to grids at 4 degree temperature with 100% humidity. After 30 seconds, grids were blotted for 5 seconds with blot force 25 and plunged into liquid ethane.
Resolution 3.18 Å
9O53 Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex bound to a small molecule inhibitor Deposited 2025-04-09 Assembly 1 Insufficient information Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain A 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Not recorded A1B8D N-(2,1,3-benzoxadiazol-4-yl)-3-(4-methoxybenzene-1-sulfonamido)benzamide × 4 K POTASSIUM ION × 4 CA CALCIUM ION × 16 ELECTRON MICROSCOPY
cryo-EM buffer pH 8；20 mM Tris pH 8, 150 mM KCl, 2 mM CaCl2, 0.005% GDN, 0.0005% CHS
cryo-EM vitrification conditions Cryogen ETHANE；5 uL of sample was applied to grids at 4 degree temperature with 100% humidity. After 30 seconds, grids were blotted for 5 seconds with blot force 25 and plunged into liquid ethane.
Resolution 3.30 Å
9O5O Cryo-EM structure of the human SK2-4 chimera/calmodulin channel complex bound to a small molecule activator Deposited 2025-04-10 Assembly 1 Insufficient information Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain A 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain B 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain C 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 1–14（14 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Chain D 305–427（123 aa） Fragment：SK4 residues 1-15 + SK2 residues 124-412 + SK4 residues 306-428
Not recorded A1B8G N-(2,1,3-benzoxadiazol-4-yl)-4-(trifluoromethyl)benzamide × 4 K POTASSIUM ION × 2 CA CALCIUM ION × 16 ELECTRON MICROSCOPY
cryo-EM buffer pH 8；20 mM Tris pH 8, 150 mM KCl, 2 mM CaCl2, 0.005% GDN, 0.0005% CHS
cryo-EM vitrification conditions Cryogen ETHANE；5 uL of sample was applied to grids at 4 degree temperature with 100% humidity. After 30 seconds, grids were blotted for 5 seconds with blot force 25 and plunged into liquid ethane.
Resolution 3.10 Å
9OA8 Cryo-EM structure of KCa3.1/calmodulin channel in complex with NS309 Deposited 2025-04-19 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 9–386（378 aa）
Chain B 9–386（378 aa）
Chain C 9–386（378 aa）
Chain D 9–386（378 aa）
Not recorded K POTASSIUM ION × 3 1KP (3E)-6,7-dichloro-3-(hydroxyimino)-1,3-dihydro-2H-indol-2-one × 4 CA CALCIUM ION × 8 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 3.59 Å
9Y5Q Cryo EM structure of KCa3.1_R355K_I/calmodulin channel in complex with rimtuzalcap Deposited 2025-09-05 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 9–386（378 aa）
Chain B 9–386（378 aa）
Chain C 9–386（378 aa）
Chain D 9–386（378 aa）
Mutation：R355K Mutation：R355K Mutation：R355K Mutation：R355K K POTASSIUM ION × 1 A1B92 Rimtuzalcap × 4 CA CALCIUM ION × 4 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 4.73 Å
9YDZ Cryo EM structure of KCa3.1_R355K_II/calmodulin channel in complex with rimtuzalcap Deposited 2025-09-23 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 9–366（358 aa）
Chain B 9–366（358 aa）
Chain C 9–366（358 aa）
Chain D 9–366（358 aa）
Mutation：R355K Mutation：R355K Mutation：R355K Mutation：R355K K POTASSIUM ION × 4 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 3.40 Å
9ZPO Cryo-EM structure of KCa3.1_I/calmodulin channel in complex with SKA31. Deposited 2025-12-16 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 9–386（378 aa）
Chain B 9–386（378 aa）
Chain C 9–386（378 aa）
Chain D 9–386（378 aa）
Not recorded A1C3Q naphtho[1,2-d][1,3]thiazol-2-amine × 4 CA CALCIUM ION × 8 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 3.67 Å
9ZPT Cryo-EM structure of KCa3.1_II/calmodulin channel in complex with SKA31. Deposited 2025-12-17 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 9–366（358 aa）
Chain B 9–366（358 aa）
Chain C 9–366（358 aa）
Chain D 9–366（358 aa）
Not recorded K POTASSIUM ION × 4 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 3.39 Å
9ZRK Cryo-EM structure of KCa3.1_I/calmodulin channel in complex with SKA111. Deposited 2025-12-20 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 9–386（378 aa）
Chain B 9–386（378 aa）
Chain C 9–386（378 aa）
Chain D 9–386（378 aa）
Not recorded A1C3U 5-methylnaphtho[1,2-d][1,3]thiazol-2-amine × 4 K POTASSIUM ION × 4 CA CALCIUM ION × 16 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 2.99 Å
9ZRL Cryo-EM structure of KCa3.1_II/calmodulin channel in complex with SKA111. Deposited 2025-12-20 Assembly 1 Protein heterocomplex Heteromer；Protein × 8 PDB declaration: octameric（8） Consistent with protein count
Chain A 9–369（361 aa）
Chain B 9–369（361 aa）
Chain C 9–369（361 aa）
Chain D 9–369（361 aa）
Not recorded K POTASSIUM ION × 4 ELECTRON MICROSCOPY
cryo-EM buffer pH 8
cryo-EM vitrification conditions Cryogen ETHANE
Resolution 3.38 Å

This page presents structural evidence recorded in PDB/mmCIF.“No recorded non-water small molecule” does not prove that the experimental sample was ligand-free; experimental conditions belong to the PDB experiment, while ligands and copy counts are shown for each biological assembly.