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in. 1 nm. Water in Nanopores. CCP5 Summer School 2002. Oliver Beckstein Laboratory of Molecular Biophysics, Oxford. Gating and Water Transport. Hydrophobic rings ( MscL , KcsA , nAChR ). Water pores ( Aqp , GlpF ). N. Unwin (2000). Model System. R M =10 Å. z. L M = 4 Å. L p =8 Å.

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1 nm

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  1. in

  2. 1 nm

  3. Water in Nanopores CCP5 Summer School 2002 Oliver Beckstein Laboratory of Molecular Biophysics, Oxford

  4. Gating and Water Transport Hydrophobic rings (MscL, KcsA, nAChR) Water pores (Aqp, GlpF) N. Unwin (2000)

  5. Model System RM=10 Å z LM=4 Å Lp=8 Å Rp Molecular Dynamics • CH4 spheres (hydrophobic) • RMSD  1 Ă • GROMACS

  6. Pore Occupancy Fluctuations Rp=5 Å Rp=6 Å Middle: Rp=5.5 Å

  7. Open state  w=1 Closed state  w=0 Openness

  8. Pore Occupancy Fluctuations Rp=5 Å <w>=0.17 Rp=5.5 Å<w>=0.28 Rp=6 Å<w>=0.77

  9. “Capillary Condensation” empty, closed filled, open

  10. Water in Narrow Pores • Dynamics (diffusion) • Kinetics (open/close times) • Free energy, chemical potential

  11. open closed Disruption of open state: topen Disruption of closed state: tclose Kinetics b=1/kBT

  12. Pore Occupancy Distribution

  13. Free Energy of Water in a Nanopore

  14. Pore, Bulk

  15. Pore, Bulk, Vapour

  16. F (Rpore=6.0 Å)

  17. F (Rpore=5.5 Å)

  18. F (Rpore=5.0 Å)

  19. F (Rpore=4.5 Å)

  20. Free Energy F

  21. Free Energy Density f

  22. Chemical Potential m • (neq) = 0: neq= 1.035 n0

  23. open closed Equilibrium and Geometry

  24. What happens? • Two independent processes: • Filling (ends the closed state): tclose • Emptying (ends the open state): topen  Occupancy fluctuations • Filling water evaporation • R independent • Emptying rupture of hydrogen- bond network by water fluctuations (“bubbles”) • volume dependent

  25. Summary/Biology… nAChRHydrophobic Gating N. Unwin (2000) R  1.4 Å Aqp/GlpF Water transport • “bulk” stabilisation: amphipathic pore • Fast diffusion • (“greasy slide”) ~20 Å

  26. The Future… With the help of… Mark Sansom José Faraldo Gómez Phil Biggin • Long term water behaviour in more complex geometries: approximating aqp, nAChR • Theoretical understanding (thermodynamics) • Behaviour of ions?

  27. RM Rp R R Hydrophobic Gating… z Geometry

  28. Pore lining apolar polar …+ Hydrophilic Pore Lining… Dipole strength peptide bond dipole

  29. R R Geometry Pore lining apolar polar …+ Hydrophobic Pore Lining Dipole strength peptide bond dipole open closed GATED OB, P. C. Biggin, M.S.P. Sansom, J. Phys. Chem. B 105 (2001)

  30. Water in Narrow Pores • Dynamics (diffusion) • Kinetics (open/close times) • Free energy z

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