Concentration Dependent Ion Selectivity in VDAC: A Molecular Dynamics Simulation Study

The voltage-dependent anion channel (VDAC) forms the major pore in the outer mitochondrial membrane. Its high conducting open state features a moderate anion selectivity. There is some evidence indicating that the electrophysiological properties of VDAC vary with the salt concentration. Using a theoretical approach the molecular basis for this concentration dependence was investigated. Molecular dynamics simulations and continuum electrostatic calculations performed on the mouse VDAC1 isoform clearly demonstrate that the distribution of fixed charges in the channel creates an electric field, which determines the anion preference of VDAC at low salt concentration. Increasing the salt concentration in the bulk results in a higher concentration of ions in the VDAC wide pore. This event induces a large electrostatic screening of the charged residues promoting a less anion selective channel. Residues that are responsible for the electrostatic pattern of the channel were identified using the molecular dynamics trajectories. Some of these residues are found to be conserved suggesting that ion permeation between different VDAC species occurs through a common mechanism. This inference is buttressed by electrophysiological experiments performed on bean VDAC32 protein akin to mouse VDAC

3rd US-European Competition and Workshop on Micro Air Vehicle Systems (MAV07) European Micro Air Vehicle Conference and Flight Competition B-UAV tracking control integrating planned yaw and longitudinal/lateral inputs

In this study the tracking controller solution for the cartesian position and orientation (yaw) of the IBISC Bidirectional-Unmanned Arial Vehicle (B-UAV) is addressed in the cartesian coordinates. With respect to velocities based control, the cartesian accelerationbased model involves some difficulties in the conception of the tracking controller. Controlling the vehicle velocities (typical example from mobile robots) leads to a stabilizing/tracking of vehicle's positions. However, the problem is not straightforward when one considers acceleration-based motion. The aim of this work was to steer the B-UAV using the yaw attitude and two inclined rotor forces. The tracking control problem considers the dynamic model in accelerations and integrates some kinematic transformations. In neighborhood of the reference path, the transformed model in errors is linearized. Hence, the tracking results are local of nature but lead to a satisfactory simulation tracking tests. The planned yaw and longitudinal/lateral inputs are also considered in the tracking control design

Lipid Dynamics and Protein–Lipid Interactions in 2D Crystals Formed with the β-Barrel Integral Membrane Protein VDAC1

We employ a combination of [superscript 13]C/[superscript 15]N magic angle spinning (MAS) NMR and [superscript 2]H NMR to study the structural and functional consequences of different membrane environments on VDAC1 and, conversely, the effect of VDAC1 on the structure of the lipid bilayer. MAS spectra reveal a well-structured VDAC1 in 2D crystals of dimyristoylphosphatidylcholine (DMPC) and diphytanoylphosphatidylcholine (DPhPC), and their temperature dependence suggests that the VDAC structure does not change conformation above and below the lipid phase transition temperature. The same data show that the N-terminus remains structured at both low and high temperatures. Importantly, functional studies based on electrophysiological measurements on these same samples show fully functional channels, even without the presence of Triton X-100 that has been found necessary for in vitro-refolded channels. [superscript 2]H solid-state NMR and differential scanning calorimetry were used to investigate the dynamics and phase behavior of the lipids within the VDAC1 2D crystals. [superscript 2]H NMR spectra indicate that the presence of protein in DMPC results in a broad lipid phase transition that is shifted from 19 to ~27 °C and show the existence of different lipid populations, consistent with the presence of both annular and bulk lipids in the functionally and structurally homogeneous samples.National Institutes of Health (U.S.) (Grant EB001960)National Institutes of Health (U.S.) (Grant EB002026)National Institutes of Health (U.S.) (Grant GM075879