Water structure in the Gramicidin A transmembrane channel.

The interaction energy and the structure of water molecules either inside the Gramicidin A transmembrane channel or at its two extremities is examined with the use of iso-energy maps and Monte Carlo simulations. The shape of the channel as experienced by water is analyzed in detail. Variations in the hydration structure due to the presence of a Na+ ion placed at several positions along the channel are simulated, analyzed and discussed. Preliminary data on Li+ and K+ interacting with Gramicidin A and the system of water molecules are reported. The Gramicidin A atomic coordinates have been taken from Urry's recent papers.