Hydrogen exchange in the lipid bilayer-bound gramicidin channel

Hydrogen exchange experiments for a membrane-bound polypeptide could lead to interesting functional and structural insights. Here, hydrogen/deuterium exchange, saturation transfer and differential relaxation experiments have been performed on oriented lipid bilayer-bound polypeptide samples to measure the exchange lifetimes. The polypeptide, gramicidin A, forms a monovalent cation selective channel across membranes. The pH dependent results suggest that the indole N epsilon 1-H groups show base catalyzed hydrogen exchange, but that the backbone amide sites are not base catalyzed, consistent with the exclusion of anions from this channel. Furthermore, the recently described [1] orientational distribution of the individual peptide carbonyls (i.e. carbonyls either tipped slightly in toward or away from the channel axis) is consistent with the observed difference in odd- and even-numbered amide residue exchange lifetimes.