【正文】 ctivity (PCa/PCl) recorded in 1 : M CaCl2 SUMMARY OF RESULTS (1) Conclusions: Taking positive charge out of the constriction zone (?= 3, see control mutant AAA) enhances the cation over anion permeability. Putting in extra negative charge (?= 5, see EAE mutant) further increases the cation selectivity. Henk Mediema Wim Meijberg 110 P Ca /P NaWT 2. 2AAA 3. 7EAE 4. 2Ca2+ over Na+ selectivity (PCa/PNa) recorded in M NaCl : M CaCl2 SUMMARY OF RESULTS (2) Conclusion: Compared to WT, EAE shows just a moderate increase of the Ca2+ over Na+ selectivity. To further enhance PCa/PNa may require additional negative charge and/or a change of the ?dielectric volume?. Work in Progress! Henk Mediema Wim Meijberg 111 Selectivity Differs in Different Types of Channels Wolfgang Nonner Dirk Gillespie Other Types of Channels 112 Ca channel Na channel Cl channel K channel prefers Small ions Ca2+ Na+ prefers Small ions Na+ Ca2+ Na+ over K+ prefers Large ions prefers K+ Na+ Selectivity filter EEEE 4 ? charges Selectivity filter DEKA 2 ?, 1+ charge Selectivity filter hydrophobic partial charges Selectivity filter single filing partial charges PNP/DFT Monte Carlo Bulk Approx Not modeled yet Selectivity of Different Channel Types The same crowded charge mechanism can explain all these different channel properties with surprisingly little extra physics. 113 Sodium Channel (with D. Boda, D. Busath, and D. Henderson) Related to Ca++ channel ? removing the positive lysine (K) from the DEKA locus makes calciumselective channel High Na+ selectivity ? 1 mM CaCl2 in M NaCl gives all Na+ current (pare to calcium channel) ? only 10 mM CaCl2 gives substantial Ca++ current Monte Carlo method is limited (so far) to a uniform dielectric Stay tuned…. Wolfgang Nonner Dirk Gillespie 114 Na+ Ca++ Na+/Ca2+ Competition in the Sodium Channel Biological Region Ca++ in bath (M) Wolfgang Nonner Dirk Gillespie 115 ?Model gives smallion selectivity. ?Result also applies to the calcium channel. Na+/Alkali Metal Competition in Na+ Channel Biological Region Wolfgang Nonner Dirk Gillespie 116 ?New? result from PNP/SPM bined analysis Spatial Nonuniformity in Na+ Channel Wolfgang Nonner Dirk Gillespie 117 Na+ vs K+ Selectivity Na+ K+ Channel Protein Protein Protein Protein Na+ Channel Wolfgang Nonner Dirk Gillespie 118 Na+ Channels Select Small Na+ over Big K+ because (we predict) Protein side chains are small allowing Small Na+ to Pack into Niches K+ is too big for the niches! Wolfgang Nonner Dirk Gillespie Summary of Na+ Channel 119 Sodium Channel Summary Na+ channel is a Poorly Selective Highly Conducting Calcium channel, which is Roughened so it prefers Small Na+ over big K+ Wolfgang Nonner Dirk Gillespie 120 Cl? Selective Channel Selective for Larger Anions The Dilute Channel Wolfgang Nonner Dirk Gillespie 121 Chloride Channel Channel prefers large anions in experiments, Low Density of Charge (several partial charges in nm3) Selectivity Filter contains hydrophobic groups ? these are modeled to (slightly) repel water ? this results in largeion selectivity Conducts only anions at low concentrations ? Conducts both anions and cations at high concentration Current depends on anion type and concentration Wolfgang Nonner Dirk Gillespie Doug Henderson Dezso Boda 122 Biological Case Chloride Channel Selectivity depends Qualitatively on concentration Wolfgang Nonner Dirk Gillespie 123 The Dilute Channel: Anion Selective Channel protein creates a Pressure difference between bath and channel Large ions like Cl– are Pushed into the channel more than smaller ions like F– Wolfgang Nonner Dirk Gillespie 124 Key: Hydrophobic Residues Repel Water giving ? Largeion selectivity (in both anion and cation channels). ? Peculiar nonmonotonic conductance properties and IV curves observed in experiments Hydrophobic repulsion can give gating. ?Vacuum lock? model of gating (M. Green, D. Henderson。 . Hansen。 Mark Sansom。 Sergei Sukarev) Chloride Channel Wolfgang Nonner Dirk Gillespie 125 Conclusion Each channel type is a variation on a theme of Crowded Charge and Electrostatics, Each channel types uses particular physics as a variation. Wolfgang Nonner Dirk Gillespie 126 Function can be predicted From Structure given Fundamental Physical Laws (sometimes, in some cases). 127 More? DFT 128 Density Functional and Poisson Nernst Planck model of Ion Selectivity in Biological Ion Channels Dirk Gillespie Wolfgang Nonner Department of Physiology and Biophysics University of Miami School of Medicine Bob Eisenberg Department of Molecular Biophysics and Physiology Rush Medical College, Chicago 129 We (following many others) have used Many Theories of Ionic Solutions as Highly Compressible Plasma of Ions with similar results MSA, SPM, MC and DFT MSA: Mean Spherical Approximation SPM: Solvent Primitive Model MC: Monte Carlo Simulation DFT: Density Functional Theory of Solutions Most Accurate Atomic Detail Inhomogeneous Systems 130 Density Functional Theory HS excess chemical potential is from free energy functional ? ?? ?? ? ? ?? ?? ? H S k H S nd?? ??? ? ??x x xEnergy density depends on “nonlocal densities” Nonner, Gillespie, Eisenberg 131 ? ?? ?? ?? ?? ?? ?? ?? ? ? ? ? ? H S kHSiiHSik T n dn????????????????? ? ???? ?xxxx x x xHS excess chemical potent