Strange et al. review recent advances in our understanding of the molecular and structural basis of volume-regulated anion channel function within the framework of classical biophysical and physiological studies.
The lumenal protein tPA modulates fusion pore expansion as chromaffin granules undergo exocytosis. Abbineni et al. show that other lumenal proteins, including chromogranin A, also regulate the lifetime of fusion pores and that protein overexpression downregulates endogenous lumenal proteins.
Phosphorylation of the ryanodine receptor 2 at serine 2030 is required for a complete β-adrenergic response
Phosphorylation is thought to play a role in modulation of the ryanodine receptor 2 channel. Using a S2030A knock-in mouse model, Potenza et al. reveal that phosphorylation of RyR2-S2030 mediates channel regulation during the β-adrenergic response.
The intracellular amino and carboxyl termini of the P2X1 receptor associate to form a cytoplasmic cap on the open state. Fryatt et al. use cysteine-reactive cross linking and molecular modeling to demonstrate structural organization of the intracellular termini in the apo and desensitized states.
Glutamate activates individual subunits of AMPA receptors in a stepwise manner. Shi et al. reveal that two noncompetitive antagonists disrupt this gating pattern and that their binding sites at the boundary between the transmembrane and extracellular linker domains is a tunable locus for gating.
Voltage-gated sodium channels have a conserved multiphase slow-inactivation process. Gamal El-Din et al. show that the early phase involves conformational changes at a critical threonine in the S6 segment, which are followed by a late phase mediated by the intracellular C-terminal domain.
Batrachotoxin (BTX) causes paralysis and death by activating “pseudosymmetric” eukaryotic sodium (Nav) channels. Finol-Urdaneta et al. investigate its action on the prokaryotic homotetrameric homologues NaChBac and NavSp1, revealing use-dependent facilitation of activation, and inhibition of deactivation, caused by BTX binding to the symmetric pore.
Mammalian hyperpolarization-activated cyclic-nucleotide–modulated (HCN) channels bind cAMP preferably in the open state. Using sea urchin HCN channels, Idikuda et al. reveal less cAMP binding to the closed state and further reduced binding to the inactivated state and thus demonstrate intricate communication between the gate and ligand-binding domain.
Some hERG channel blockers are clinically safe, but others cause fatal cardiac arrhythmias. Furutani et al. show that safe blockers facilitate channel opening in ventricular myocytes and provide a repolarization reserve at precisely the voltages and times needed to suppress arrhythmias.
Extracellular protons accelerate hERG channel deactivation by destabilizing voltage sensor relaxation
The human ether-à-go-go–related gene (hERG) encodes a delayed rectifier K+ channel with slow deactivation gating. Shi et al. find that acidic residues on S3 contribute to slow deactivation kinetics by stabilizing the relaxed state of the voltage sensor, which can be mitigated by extracellular protons.
Epilepsy-associated mutations in the voltage sensor of KCNQ3 affect voltage dependence of channel opening
KCNQ2 and KCNQ3 are subunits of the M channel, which regulates neuronal excitability. Using voltage clamp fluorometry, Barro-Soria reveals that the R230C mutation in KCNQ3, which causes hyperexcitability, shifts the voltage dependence of the open/closed transition to negative potentials.
Reinterpretation of the substrate specificity of the voltage-sensing phosphatase during dimerization
Ciona intestinalis voltage-sensing phosphatase (VSP) has lipid 5- and 3-phosphatase activity, but 3-phosphatase is evident only at high VSP concentrations. Using kinetic modeling including endogenous lipid metabolizing enzymes and VSP phosphatase activities, Kruse et al. show how apparent activation of 3-phosphatase at high concentrations arises.
Methods and Approaches
Xenopus laevis oocytes are used to study membrane proteins because of their ability to translate exogenous mRNA, but their high intrinsic fluorescence limits fluorescence recordings. Lee and Bezanilla present two methods to increase the amount of melanin and reduce background fluorescence in oocytes.