Figure 2.

Charge density and cAMP mass density profiles from voltage simulations. (a) Charge density of protein, lipids, total ions, and individual charged groups (K⁺, Cl⁻, cAMP, Mg²⁺) along the channel z axis from the −200 mV simulation. (b) Volumetric mass density of cAMP from −200 mV simulation. Density higher than bulk is shown (green to red color representing low to high). (c) Boltzmann inversion of the cAMP 2D-density (log-density) along the channel z axis and radial distance $R=\sqrt{{\left(x_{cAMP}\right)}^2+{\left(y_{cAMP}\right)}^2}$ from channel center axis (x,y = 0,0). (d) 1D log-density of the cAMP within the pore along z axis. Arrows indicate the direction of cAMP flux at each voltage. Note that a log-density profile is not a PMF (see PMFs under voltage in Fig. 5). To see this figure in color, go online.