Cover picture: Molecular dynamics simulations of water permeation through gramicidin A. Water permeation was found to occur at a higher rate through the double helical conformation (right) than through the helical dimer conformation (left). The simulations further show that desformylation of the peptide, resulting in a positive charge on the N termini, shifts the equilibrium between the two conformations towards the double helical conformation (bottom). Together, these results rationalize the 100-fold experimentally observed increased water permeability of desformylated compared to native gramicidin A. See the article by de Groot et al. on p. 2934.