Water permeation through gramicidin A: desformylation and the double helix: a molecular dynamics study.
Multinanosecond molecular dynamics simulations of gramicidin A embedded in a dimyristoylphosphatidylcholine bilayer show a remarkable structural stability for both experimentally determined conformations: the head-to-head helical dimer and the double helix. Water permeability was found to be much higher in the double helical conformation, which is explained by lower hydrogen bond-mediated enthalpic barriers at the channel entrance and its larger pore size. Free-energy perturbation calculations show that the double helical structure is stabilized by the positive charges at the N termini introduced by the desformylation, whereas the helical dimer is destabilized. Together with the recent experimental observation that desformyl gramicidin conducts water hundredfold better than gramicidin, this suggests that desformyl gramicidin A predominantly occurs in the double helical conformation.
de Groot
Bert L
BL
Theoretical Molecular Biophysics Group, Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. bgroot@gwdg.de
Tieleman
D Peter
DP
Pohl
Peter
P
Grubmüller
Helmut
H
D055592:Biophysical Phenomena; D001703:Biophysics; D004134:Dimyristoylphosphatidylcholine; D004355:Drug Stability; D006096:Gramicidin / Q000737:chemistry*; D006860:Hydrogen Bonding; D007473:Ion Channels / Q000737:chemistry; D008051:Lipid Bilayers; D008958:Models, Molecular; D010539:Permeability; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
D007473:Ion Channels; D008051:Lipid Bilayers; D014867:Water; D006096:Gramicidin; D004134:Dimyristoylphosphatidylcholine