Cornell

Basilio D, Noack K, Picollo A, Accardi A. Conformational changes required for H(+)/Cl(-) exchange mediated by a CLC transporter. Nat Struct Mol Biol 2014; 21(5):456-63

The CLC-type H+/Cl- exchangers of the CLC family of Cl- channels and transporters play key roles in the acidification of intracellular compartments such as endosomes and lysosomes. Mutations in several human CLC genes impair Cl- transport causing genetic diseases. However, the transport mechanism of the CLCs remains poorly understood. Most transporters undergo large-scale conformational changes that result in the alternate opening of two “gates” to expose substrate to either side of the membrane, the alternating-access paradigm. In contrast, the CLCs are thought to undergo extremely limited conformational rearrangements: a single glutamate side chain moves in and out of the transport pathway, suggesting that in the CLCs this residue serves as the sole gate. We show that the CLC transporters have two gates: the external gate is formed by the glutamate and the internal gate is formed by a conserved tyrosine. The presence of a non-protonatable inner gate is necessary to allow the CLCs to sustain tight coupling at the acidic pHs encountered during the acidification of intracellular compartments.

Herold KF, Sanford RL, Lee W, Schultz MF, Ingólfsson HI, Andersen OS, Hemmings HC Jr. Volatile anesthetics inhibit sodium channels without altering bulk lipid bilayer properties. J Gen Physiol 2014; 144(6):545-60
A major debate has divided the anesthesia research community into two camps: one believing that anesthetics act primarily on the cell membrane (the lipid bilayer) of nerve cells, perhaps altering it to the point that embedded proteins cannot function normally, and the other that the membrane proteins themselves are altered directly by anesthetics. This report provides new evidence supporting the latter position that it is the proteins that are affected by commonly used anesthetics. This is the first demonstration that anesthetics alter the function of ion channels without altering properties of the cell membranes.

Hudson AE, Calderon DP, Pfaff DW, Proekt A. Recovery of consciousness is mediated by a network of discrete metastable activity states. Proc Natl Acad Sci USA 2014; 111(25):9283-8
How does the brain recover consciousness after significant perturbations such as anesthesia? The simplest answer is that as the anesthetic washes out, the brain follows a steady and monotonic path toward consciousness. We show that this simple intuition is incorrect. We varied the anesthetic concentration to parametrically control the magnitude of perturbation to brain dynamics while analyzing the characteristics of neuronal activity during recovery of consciousness. We find that, en route to consciousness, the brain passes through several discrete activity states. Although transitions between certain of these activity states occur spontaneously, transitions between others are not observed. Thus, the network formed by these state transitions gives rise to an ordered sequence of states that mediates recovery of consciousness.

McCoy JG, Rusinova R, Kim DM, Kowal J, Banerjee S, Jaramillo Cartagena A, Thompson AN, Kolmakova-Partensky L, Stahlberg H, Andersen OS, Nimigean CM. A KcsA/MloK1 chimeric ion channel has lipid-dependent ligand-binding energetics. J Biol Chem 2014; 289(14):9535-46
Pacemaker activity and visual and olfactory signaling are directly controlled through HCN and CNG ion channels. Channel activity is regulated by cAMP and cGMP binding to cytoplasmic cyclic nucleotide-binding domains. The mechanism by which this process occurs is poorly understood due to the inability to produce and purify these channels. We have shown that a chimeric construct combining the well-studied pH-gated potassium channel KcsA and the cyclic nucleotide binding domains of a prokaryotic cyclic nucleotide-modulated channel MloK1 results in a high yield protein which features both cAMP- and pH-induced activation. Using this construct we were able to show that the cyclic nucleotide-binding domains and pore helices are sufficient for cAMP-induced activation and that cAMP binding is a bilayer-dependent process.

Platholi J, Herold KF, Hemmings HC Jr, Halpain S. Isoflurane reversibly destabilizes hippocampal dendritic spines by an actin-dependent mechanism. PLoS One 2014; 9(7):e102978.
Although commonly used in a clinical setting, the mechanism of action of isoflurane or other general anesthetics is unknown. Increasing evidence suggests that general anesthesia may be associated with persistent cognitive impairments in early development or postoperatively in maturity. This study investigates the effects of isoflurane on morphology and stability of dendritic spines, a structure critical for synaptic plasticity. We show that a clinically relevant concentration and duration of isoflurane results in transient reductions in spine area and spine number, and that these changes are mediated by destabilization of the underlying actin cytoskeleton. These findings implicate dendritic spines as a pharmacological substrate for the synaptic actions of isoflurane. Actin filament destabilization provides a molecular and structural basis for anesthetic effects on synaptic transmission and function consistent with emerging concepts of synaptic plasticity. A fundamental understanding of isoflurane action will have both clinical and pharmacological significance to anesthesia, learning and memory, and consciousness.