Table 1. Ion selectivity values and conductance asymmetry ratios of the OccD proteins. a.
gO1 and gO2 represent single-channel conductance values corresponding to the open sub-states O1 and O2, respectively. The single-channel conductance that corresponds to the most probable open sub-state is shown in bold. These parameters were calculated using a transmembrane applied potential of +60 mV. g’s were given in pS. The asymmetry conductance ratios of the most probable sub-state (g80/g−80) at +80 mV to that at −80 mV were determined in 1M KCl, 10 mM potassium phosphate, pH=7.4. The reversal potential (Vr) is the applied transmembrane potential that offsets the resting potential of the channel under KCl concentration gradient conditions. The reversal potential values were measured when the concentrations of KCl in cis and trans were 0.2 M and 1M, respectively, under similar conditions of buffer and pH (10 mM potassium phosphate, pH=7.4). Permeability ratios (Pk/PCl) were calculated based upon the reversal potential Vr, as discussed in the main text [31; 32; 49]. The reversal potential of the OccD1 and OccD2 channels were determined by eliminating the high-conductance state.
| Protein | g01 (pS) | g02 (pS) | g80/g−80 | Vr (mV) | Pk/PCl | Selectivity |
|---|---|---|---|---|---|---|
| OccD1 | 21 ± 3 | 889 ± 102 | 2.58 ± 0.97 | −15 ± 7 | 2.5 ± 1.0 | Cation-selective |
| OccD2 | NAb | NAb | 0.99 ± 0.30 | −20 ± 8 | 3.5 ± 1.5 | Cation-selective |
| OccD3 | 3.0 ± 3.0 | 667 ± 71 | 2.55 ± 0.26 | −18 ± 1 | 3.0 ± 0.2 | Cation-selective |
| OccD4 | 3.0 ± 0.1 | 159 ± 8 | 1.11 ± 0.08 | −20 ± 2 | 3.5 ± 0.5 | Cation-selective |
| OccD5 | 24 ± 11 | 239 ± 34 | 0.42 ± 0.08 | −32 ± 3 | 12 ± 4 | Cation-selective |
| OccD6 | 417 ± 117 | 1889 ± 151 | 0.99 ± 0.16 | −24 ± 4 | 5.0 ± 1.4 | Cation-selective |
The crystal structures of the OccD4, OccD5 and OccD6 proteins are not available.
The baseline that corresponds to the O1 open sub-state in various single-channel experiments varied between 2 and 17 pA when the applied transmembrane potential of +60 mV. Therefore, were not able to determine these values with satisfactory accuracy.