Biological Assembly 1  

 3D View: Structure | Electron Density | Ligand Interaction

Global Symmetry: Asymmetric - C1 
Global Stoichiometry: Hetero 2-mer - A1B1 

Biological assembly 1 assigned by authors and generated by PISA (software)

Macromolecule Content

• Total Structure Weight: 24.71 kDa 
• Atom Count: 1360 
• Residue Count: 168 
• Unique protein chains: 2

4GOW

Crystal Structure of Ca2+/CaM:Kv7.4 (KCNQ4) B helix complex

• DOI: 10.2210/pdb4GOW/pdb

• Classification: PROTEIN BINDING
• Organism(s): Homo sapiens
• Expression System: Escherichia coli
• Mutation(s): No 


• Deposited: 2012-08-20 Released: 2012-12-12 
• Deposition Author(s): Xu, Q., Chang, A., Tolia, A., Minor Jr., D.L.

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Experimental Data Snapshot

• Method: X-RAY DIFFRACTION
• Resolution: 2.60 Å
• R-Value Free: 0.268 
• R-Value Work: 0.236 
• R-Value Observed: 0.238 

Literature

Structure of a Ca(2+)/CaM:Kv7.4 (KCNQ4) B-helix complex provides insight into M current modulation.

Xu, Q., Chang, A., Tolia, A., Minor, D.L.

(2013) J Mol Biol 425: 378-394

• PubMed: 23178170 
• DOI: 10.1016/j.jmb.2012.11.023
• Primary Citation of Related Structures:  
  4GOW


• PubMed Abstract: 
  

Calmodulin (CaM) is an important regulator of Kv7.x (KCNQx) voltage-gated potassium channels. Channels from this family produce neuronal M currents and cardiac and auditory I(KS) currents and harbor mutations that cause arrhythmias, epilepsy, and deafness. Despite extensive functional characterization, biochemical and structural details of the interaction between CaM and the channel have remained elusive. Here, we show that both apo-CaM and Ca(2+)/CaM bind to the C-terminal tail of the neuronal channel Kv7.4 (KCNQ4), which is involved in both hearing and mechanosensation. Interactions between apo-CaM and the Kv7.4 tail involve two C-terminal tail segments, known as the A and B segments, whereas the interaction between Ca(2+)/CaM and the Kv7.4 C-terminal tail requires only the B segment. Biochemical studies show that the calcium dependence of the CaM:B segment interaction is conserved in all Kv7 subtypes. X-ray crystallographic determination of the structure of the Ca(2+)/CaM:Kv7.4 B segment complex shows that Ca(2+)/CaM wraps around the Kv7.4 B segment, which forms an α-helix, in an antiparallel orientation that embodies a variation of the classic 1-14 Ca(2+)/CaM interaction motif. Taken together with the context of prior studies, our data suggest a model for modulation of neuronal Kv7 channels involving a calcium-dependent conformational switch from an apo-CaM form that bridges the A and B segments to a Ca(2+)/CaM form bound to the B-helix. The structure presented here also provides a context for a number of disease-causing mutations and for further dissection of the mechanisms by which CaM controls Kv7 function.

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Organizational Affiliation: 

Cardiovascular Research Institute, University of California, San Francisco, CA 94158-2156, USA.

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
Calmodulin	D	144	Homo sapiens	Mutation(s): 0  Gene Names:  CALM1, CALM, CAM, CAM1, CALM2, CAM2, CAMB, CALM3, CALML2, CAM3, CAMC, CAMIII
Find proteins for P0DP23 (Homo sapiens) Explore P0DP23  Go to UniProtKB:  P0DP23
NIH Common Fund Data Resources
PHAROS:  P0DP23 GTEx:  ENSG00000198668

Entity ID: 2
Molecule	Chains	Sequence Length	Organism	Details	Image
Potassium voltage-gated channel subfamily KQT member 4	A	72	Homo sapiens	Mutation(s): 0  Gene Names: KCNQ4
Find proteins for P56696 (Homo sapiens) Explore P56696  Go to UniProtKB:  P56696
NIH Common Fund Data Resources
PHAROS:  P56696 GTEx:  ENSG00000117013

Small Molecules

Ligands 1 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram
CA	D	CALCIUM ION Ca BHPQYMZQTOCNFJ-UHFFFAOYSA-N

Experimental Data & Validation

Experimental Data

• Method: X-RAY DIFFRACTION
• Resolution: 2.60 Å
• R-Value Free: 0.268 
• R-Value Work: 0.236 
• R-Value Observed: 0.238 
• Space Group: P 6₅ 2 2

Unit Cell:

Length ( Å )	Angle ( ˚ )
a = 104.075	α = 90
b = 104.075	β = 90
c = 113.729	γ = 120

Software Package:

Software Name	Purpose
MOSFLM	data reduction
SCALA	data scaling
PHENIX	refinement
PDB_EXTRACT	data extraction
HKL-2000	data collection
PHASER	phasing

Structure Validation

Entry History 

Deposition Data

• Deposited Date: 2012-08-20 
• Released Date: 2012-12-12 
Deposition Author(s): Xu, Q., Chang, A., Tolia, A., Minor Jr., D.L.

Revision History 

• Version 1.0: 2012-12-12
  Type: Initial release
  
• Version 1.1: 2013-05-22
  Changes: Database references