3FFQ: Hcn2i 443-640 Apo-State

Visualizing conformational dynamics in proteins has been difficult, and the atomic-scale motions responsible for the behavior of most allosteric proteins are unknown. Here we report that fluorescence resonance energy transfer (FRET) between a small fluorescent dye and a nickel ion bound to a dihistidine motif can be used to monitor small structural rearrangements in proteins. This method provides several key advantages over classical FRET, including the ability to measure the dynamics of close-range interactions, the use of small probes with short linkers, a low orientation dependence, and the ability to add and remove unique tunable acceptors. We used this 'transition metal ion FRET' approach along with X-ray crystallography to determine the structural changes of the gating ring of the mouse hyperpolarization-activated cyclic nucleotide-regulated ion channel HCN2. Our results suggest a general model for the conformational switch in the cyclic nucleotide-binding site of cyclic nucleotide-regulated ion channels.
PDB ID: 3FFQDownload
MMDB ID: 73838
PDB Deposition Date: 2008/12/4
Updated in MMDB: 2012/09
Experimental Method:
x-ray diffraction
Resolution: 2.4  Å
Source Organism:
Similar Structures:
Biological Unit for 3FFQ: tetrameric; determined by author and by software (PISA)
Molecular Components in 3FFQ
Label Count Molecule
Proteins (4 molecules)
Potassium/sodium Hyperpolarization-activated Cyclic Nucleotide-gated Channel 2(Gene symbol: Hcn2)
Molecule annotation
Chemicals (20 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB