Dresden 2006 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 28: Biological Systems
CPP 28.1: Vortrag
Freitag, 31. März 2006, 10:30–10:45, ZEU Lich
Can hydrophobically lined channels be gated by water? — •K. Myriam Kroll1,2 and Roland Roth1,2 — 1Max-Planck-Institut für Metallforschung, Heisenbergstr. 3, 70569 Stuttgart — 2ITAP, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart
Pores of KcsA ion channels possess a hydrophobic region which changes its conformation between a wide pore, when open, to a narrower pore, when closed. Recent studies indicate that a hydrophobic pore can "gate" by capillary evaporation. With this mechanism water is expelled from the permeation pathway and ion flow is thereby stopped although the pore remains wider than the water or ion diameters. We study the connection between geometrical change of a hydrophobic pore and capillary evaporation to estimate the energetics of this gating mechanism in a realistic pore geometry, e.g. the energy it takes to remove the water from the pore and the force exerted by the water on the wall of the pore.
To this end we perform, in a first step, microscopic density functional theory (DFT) calculations, in which we focus on the density profile of water as capillary evaporation takes place. The insight gained from these DFT calculations we transfer and exploit, in a second step, in our mesoscopic morphometric approach. In morphometry the free energy of a liquid confined in a pore is expressed by four terms that describe the geometry of the pore and corresponding thermodynamic coefficients. This separation of geometry and thermodynamics makes calculations very efficient so that effects due to change in geometry can be studied in depth. Both DFT and morphometry have been applied with great success in studies of the physics of confined fluids.