PDBsum entry 2ovc

Transport protein

PDB id

2ovc

Contents

			Protein chain

					30 a.a.

			Waters ×18

References listed in PDB file

Key reference

Title

Structural insight into kcnq (kv7) channel assembly and channelopathy.

Authors

R.J.Howard, K.A.Clark, J.M.Holton, D.L.Minor.

Ref.

Neuron, 2007, 53, 663-675. [DOI no: 10.1016/j.neuron.2007.02.010]

PubMed id

17329207

Abstract

Kv7.x (KCNQ) voltage-gated potassium channels form the cardiac and auditory I(Ks) current and the neuronal M-current. The five Kv7 subtypes have distinct assembly preferences encoded by a C-terminal cytoplasmic assembly domain, the A-domain Tail. Here, we present the high-resolution structure of the Kv7.4 A-domain Tail together with biochemical experiments that show that the domain is a self-assembling, parallel, four-stranded coiled coil. Structural analysis and biochemical studies indicate conservation of the coiled coil in all Kv7 subtypes and that a limited set of interactions encode assembly specificity determinants. Kv7 mutations have prominent roles in arrhythmias, deafness, and epilepsy. The structure together with biochemical data indicate that A-domain Tail arrhythmia mutations cluster on the solvent-accessible surface of the subunit interface at a likely site of action for modulatory proteins. Together, the data provide a framework for understanding Kv7 assembly specificity and the molecular basis of a distinct set of Kv7 channelopathies.



	Figure 2. Figure 2. Hydrophobic and Electrostatic Contacts in the Kv7.4 Coiled-Coil Domain (A) Hydrophobic layers of the coiled-coil core. Van der Waals spheres depicting the side chains of the “a” (blue) and “d” (pink) layers on a ribbon backbone (gray) are shown. The N- and C-terminal ends of the coiled coil are indicated. (B) Geometry of individual coiled-coil “a” and “d” layers. Top pictograms represent “a” (right) and “d” layers (left). Arrows show the direction from the N to C terminus, open circles represent the C[α] atoms, and black circles the C[β] atoms. Ball-and-stick representations show each layer of the core. Van der Waals spheres indicate core residues, colored as in (A). (C) Intra- and intermolecular electrostatic interactions. Ribbon diagram of tetramer with helices colored as in Figure 1D shows network 1 and network 2 interactions between the side chains (shown as sticks) of the green and orange subunits. Salt bridges (black lines) and hydrogen bonds (dotted lines) are indicated. Side chain labels are color coded to indicate the subunit of origin.		Figure 4. Figure 4. Comparing Interactions in Alternate Kv7 Subtypes (A) Stoichiometry of coiled-coil assembly domains in all five Kv7 subtypes shown by Superdex200 (Amersham Biosciences) size exclusion chromatography. Normalized absorbance is plotted against elution volume V[E] corrected for void elution volume V[0] as in Figure 3B. All samples were loaded at a concentration of 50 μM. Vertically displaced chromatograms show traces for, from top to bottom, Kv7.1 (black), Kv7.2 (orange), Kv7.3 (purple), Kv7.4 (green), Kv7.5 (pink), and MBP (gray). Vertical dotted lines indicate the predicted elution volumes of tetrameric (red) and monomeric (blue) fusion proteins. (Inset) Standard curve used to calculate molecular weight of eluted proteins on the Superdex200 column. Molecular weights for each are as follows (observed ± SD, expected monomer, expected tetramer); Kv7.1 (180 ± 2 kD, 49.4 kD, 198 kD); Kv7.2 (203 ± 6 kD, 49.3 kD, 197 kD); Kv7.3 (90.3 ± 2 kD, 49.9 kD, 200 kD); Kv7.4 (207 ± 6 kD, 48.8 kD, 195 kD); Kv7.5 (191 ± 6 kD, 48.9 kD, 196 kD). (B) Comparative interaction mapping in all subtypes. Column labels identify residue types involved in hydrophobic “a” (blue) and “d” (pink) layer contacts and electrostatic interactions (green) observed in the Kv7.4 coiled-coil structure. Filled boxes in table indicate entirely conserved interactions; shaded boxes indicate nonconserved residues that are still capable of interacting as predicted; white boxes indicate unfavorable contacts. Electrostatic interactions involved in networks 1 and 2 are indicated below the alignment. (C) Stoichiometry of mutant coiled-coil assembly domains as determined by size exclusion. Kv7.3 A-domain Tail mutants F622L and D631S/G633E restore tetramerization. Molecular weights for each are as follows (observed, expected monomer, expected tetramer); Kv7.3 (90.3 kD, 49.9 kD, 200 kD); Kv7.3 F622L (212 kD, 49.9 kD, 200 kD); Kv7.3 D631S/G633E (208 kD, 49.9 kD, 200 kD). All samples were loaded onto the column at a concentration of 50 μM.

PROCHECK

	Headers