From Flux to Function: Extracting Mechanistic Insights from Ion Channels via I-V and I-μ Analyses

Figures

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  Figure 1.. Intermediates states (nodes) and transitions (edges) highlighting kinetic network connectivity for channels with (A) 2 binding sites (2-site model) and (B) 3 binding sites (3-site model).

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  Figure 2.. Two types of mirror symmetric systems. (A) Protein with two binding sites. (B) Rate mirror symmetry with different binding, release, and transfer barriers that are the same in the two directions. (C) Mirror symmetry of voltage sensitivity showing Δφ values for inward flux. Black filled circles represent binding sites and red circles represent transition states.

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  Figure 3.. (A) Conductance curves, (B) I-V curves, and (C-F) corresponding populations for the three distinct conductance shapes. Conductance shape 1 (black) is the result of relatively equal fluxes resulting in increasing partial occupancy populations (C). Conductance shape 2 (red) reflects either a binding FLS (D) or a release FLS. Conductance shape 3 (green) reflects either a transfer FLS (E) or simultaneous binding and release FLSs (F). All population plots are equally scaled (y axis between 0 and 1).

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  Figure 4.. The influence of (A) binding, (B) transfer, and (C) release rate constants on concentration-driven (I-μ) flux (top) and chemical conductance (bottom). The black line shows the flux of a perfectly rate-symmetric system. 0.01x, 1x, and 100x refer to the scaling of the named rates relative to the other rates. Note the scale of release (C) is magnified to capture the subtle difference between 0.01x and 100x.

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  Figure 5.. Rectification due to rate asymmetry when the stability of S1 is increased by 2 kcal/mol (solid) relative to symmetric rates (dashed). Rectification is apparent in I-μ curves (yellow), but hidden in I-V curves where symmetric and asymmetric overlap, indicating negligible voltage rectification. x-axis is voltage for I-V curves and equivalent voltage for I-μ curves.

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  Figure 6.. (A) Voltage-induced rectification due to moving extracellular binding site (S2) towards intracellular side, increasing voltage coupling for extracellular binding and release while decreasing it for transfer from S1 to S2. (B) Representative site and Δφ locations depicted on model membrane with the S2 location colors matching the colors of the resulting I-V curves in (A).

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  Figure 7.. (A) Voltage-induced rectification due to moving transition state between S2 and extracellular bulk towards S2, progressively increasing voltage coupling of binding. (B) Representative transition state depicted on model membrane with colors matching the colors of the resulting I-V curves in (A).

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  Figure 8.. I-V (blue) and I-μ (yellow) curves for (A) solution 9 and (B) solution 12.

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  Figure 9.. Conductance of the ion flux (Figure 8 blue) for solution 9 (black) and solution 12 (red dashed) at (A) low magnitudes of the voltage and (B) an extended voltage range.