Structural, biochemical, and functional characterization of the cyclic nucleotide binding homology domain from the mouse EAG1 potassium channel.
KCNH channels are voltage-gated potassium channels with important physiological functions. In these channels, a C-terminal cytoplasmic region, known as the cyclic nucleotide binding homology (CNB-homology) domain displays strong sequence similarity to cyclic nucleotide binding (CNB) domains. However, the isolated domain does not bind cyclic nucleotides. Here, we report the X-ray structure of the CNB-homology domain from the mouse EAG1 channel. Through comparison with the recently determined structure of the CNB-homology domain from the zebrafish ELK (eag-like K(+)) channel and the CNB domains from the MlotiK1 and HCN (hyperpolarization-activated cyclic nucleotide-gated) potassium channels, we establish the structural features of CNB-homology domains that explain the low affinity for cyclic nucleotides. Our structure establishes that the "self-liganded" conformation, where two residues of the C-terminus of the domain are bound in an equivalent position to cyclic nucleotides in CNB domains, is a conserved feature of CNB-homology domains. Importantly, we provide biochemical evidence that suggests that there is also an unliganded conformation where the C-terminus of the domain peels away from its bound position. A functional characterization of this unliganded conformation reveals a role of the CNB-homology domain in channel gating.
Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
Maria J
MJ
Marques-Carvalho
Nirakar
N
Sahoo
Frederick W
FW
Muskett
Ricardo S
RS
Vieira-Pires
Guillaume
G
Gabant
Martine
M
Cadene
Roland
R
Schönherr
João H
JH
Morais-Cabral
D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D051638:Ether-A-Go-Go Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D009712:Nucleotides, Cyclic / Q000737:chemistry*; D011188:Potassium / Q000378:metabolism; D017434:Protein Structure, Tertiary
D051638:Ether-A-Go-Go Potassium Channels; C496885:Kcnh1 protein, mouse; D009712:Nucleotides, Cyclic; D011188:Potassium