Thermodynamics Of Voltage Dependent Gating Of Ion Channels PDF Download

Voltage-gated ion channels (VGICs) constitute an evolutionary diverse family of integral membrane proteins that transport ions across the hydrophobic membrane bilayers, when triggered by changes in membrane potential. This thesis examines the manifestations of the fundamental laws of thermodynamics on this family of proteins to understand how they operate at the molecular level. In the first few Chapters of this thesis, I describe an analytical approach to extract the energetics of voltage-dependent activation of ion channels and use it to determine the interaction energies between residues in the exemplar Shaker KV channel. The approach involves extracting a special parameter, the median voltage of activation (VM) from experimentally measured gating-charge displacement vs voltage (QV) curves. Next, I use this approach to determine the interaction energies between residues comprising an intersubunit gating nexus, which is likely to be crucial for the relay of structural and energetic information, from the voltage-sensors to the pore. Additionally, I describe how these thermodynamic principles can be extended to deconstruct the allosteric linkage pathways between voltage and ligand dependent activation pathways of polymodal allosteric channels. In the final chapter of this thesis, I study the mechanism by which temperature modulates voltage-dependent gating of ion channels. Gating of some members of the VGIC superfamily is exquisitely sensitive to changes in temperature, however we lack an understanding of the molecular mechanisms underlying temperature sensation and modulation of voltage-dependent channel function. I use a heuristic approach to systematically engineer mutations into the relatively temperature insensitive Shaker KV channel to design a temperature modulated voltage-dependent channel. From the characterization of the relative open probability vs voltage curves of over fifty mutants of the channel at two different temperatures, I propose that thermal sensitivity is mediated by state dependent changes in the solvation status of critical residues, which governs CP of channel gating. I also demonstrate that voltage-sensing charges play a crucial although indirect role in governing the effect of temperature on channel gating. These principles could be very useful to deconstruct the temperature sensing mechanisms of natively thermosensitive channels, such as the thermoTRPs and other structurally unrelated channels, such as Anoctamins.