Structure of the CLC-1 chloride channel from Homo sapiens.

CLC channels mediate passive Cl- conduction, while CLC transporters mediate active Cl- transport coupled to H+ transport in the opposite direction. The distinction between CLC-0/1/2 channels and CLC transporters seems undetectable by amino acid sequence. To understand why they are different functionally we determined the structure of the human CLC-1 channel. Its 'glutamate gate' residue, known to mediate proton transfer in CLC transporters, adopts a location in the structure that appears to preclude it from its transport function. Furthermore, smaller side chains produce a wider pore near the intracellular surface, potentially reducing a kinetic barrier for Cl- conduction. When the corresponding residues are mutated in a transporter, it is converted to a channel. Finally, Cl- at key sites in the pore appear to interact with reduced affinity compared to transporters. Thus, subtle differences in glutamate gate conformation, internal pore diameter and Cl- affinity distinguish CLC channels and transporters

The mechanosensitive ion channel TRAAK is localized to the mammalian node of Ranvier.

TRAAK is a membrane tension-activated K+ channel that has been associated through behavioral studies to mechanical nociception. We used specific monoclonal antibodies in mice to show that TRAAK is localized exclusively to nodes of Ranvier, the action potential propagating elements of myelinated nerve fibers. Approximately 80 percent of myelinated nerve fibers throughout the central and peripheral nervous system contain TRAAK in what is likely an all-nodes or no-nodes per axon fashion. TRAAK is not observed at the axon initial segment where action potentials are first generated. We used polyclonal antibodies, the TRAAK inhibitor RU2 and node clamp amplifiers to demonstrate the presence and functional properties of TRAAK in rat nerve fibers. TRAAK contributes to the leak K+ current in mammalian nerve fiber conduction by hyperpolarizing the resting membrane potential, thereby increasing Na+ channel availability for action potential propagation. We speculate on why nodes of Ranvier contain a mechanosensitive K+ channel

A Gating Charge Transfer Center in Voltage Sensors

Voltage sensors regulate the conformations of voltage-dependent ion channels and enzymes. Their nearly switchlike response as a function of membrane voltage comes from the movement of positively charged amino acids, arginine or lysine, across the membrane field. We used mutations with natural and unnatural amino acids, electrophysiological recordings, and x-ray crystallography to identify a charge transfer center in voltage sensors that facilitates this movement. This center consists of a rigid cyclic "cap" and two negatively charged amino acids to interact with a positive charge. Specific mutations induce a preference for lysine relative to arginine. By placing lysine at specific locations, the voltage sensor can be stabilized in different conformations, which enables a dissection of voltage sensor movements and their relation to ion channel opening

Pixilated figments

Exploring animation as research creation, this project combines pixilation animation and analogue lenticular printing to explore how film can have a unique in-person viewing experience without screens. For artists working with the moving image as a medium, single-channel installation and projection have become the preferred modes of display. This project seeks to provide an untethered, re-materialized and immersive analogue viewing and making experience in an era of increasing digital interfaces. It reflectively analyzes the links between handmade art practices and the moving image. Personal experiences of time and memory will also be analyzed against the moving image and its mode of display. Although display formats of moving image work have long histories of change, the mode in which they are displayed and produced has largely remained tethered to screens or projections. Lenticulars are one technique I have used to explore this problem. Instead of screens and projections, they serve more as windows, windows into the wonder of discovery that pixilation has previously established in film. This paper questions expectations for experiences, especially pertaining to viewing moving image work in person. It questions people's engagement with moving image work and how this engagement might be made more inviting. It compares the modes in which we can transmit video and offers a contemplative proposal of a new life for the moving image. By using lenticular animation to bring the moving image into plastic practices, the thesis gives the moving image a unique container

The Molecular Basis of Texture in Mashed Potato

Mash production often involves thermal pre-treatments (pre-cooks) that are designed to increase the physical strength and restrict cell separation of cooked potatoes prior to mashing. This improves the mash quality. During pre-cooking, the control of starch swelling pressures during cooking and/or the activation of pectin methylesterase (PME) prior to cooking can occur. The aim of this thesis was to examine changes in texture of cooked potatoes caused by these pre-cook treatments prior to mashing. Cooking was carried out in laboratory conditions. During steam cooking (one-stage cooking) the potatoes quickly reached 60-6

Two Separate Interfaces between the Voltage Sensor and Pore Are Required for the Function of Voltage-Dependent K+ Channels

Voltage-dependent K+ (Kv) channels gate open in response to the membrane voltage. To further our understanding of how cell membrane voltage regulates the opening of a Kv channel, we have studied the protein interfaces that attach the voltage-sensor domains to the pore. In the crystal structure, three physical interfaces exist. Only two of these consist of amino acids that are co-evolved across the interface between voltage sensor and pore according to statistical coupling analysis of 360 Kv channel sequences. A first co-evolved interface is formed by the S4-S5 linkers (one from each of four voltage sensors), which form a cuff surrounding the S6-lined pore opening at the intracellular surface. The crystal structure and published mutational studies support the hypothesis that the S4-S5 linkers convert voltage-sensor motions directly into gate opening and closing. A second co-evolved interface forms a small contact surface between S1 of the voltage sensor and the pore helix near the extracellular surface. We demonstrate through mutagenesis that this interface is necessary for the function and/or structure of two different Kv channels. This second interface is well positioned to act as a second anchor point between the voltage sensor and the pore, thus allowing efficient transmission of conformational changes to the pore's gate

A Gating Charge Transfer Center in Voltage Sensors

Voltage sensors regulate the conformations of voltage-dependent ion channels and enzymes. Their nearly switchlike response as a function of membrane voltage comes from the movement of positively charged amino acids, arginine or lysine, across the membrane field. We used mutations with natural and unnatural amino acids, electrophysiological recordings, and x-ray crystallography to identify a charge transfer center in voltage sensors that facilitates this movement. This center consists of a rigid cyclic "cap" and two negatively charged amino acids to interact with a positive charge. Specific mutations induce a preference for lysine relative to arginine. By placing lysine at specific locations, the voltage sensor can be stabilized in different conformations, which enables a dissection of voltage sensor movements and their relation to ion channel opening