HYDROGEN-EXCHANGE IN THE LIPID BILAYER-BOUND GRAMICIDIN CHANNEL

Hydrogen exchange experiments for a membrane-bound polypeptide could l ead to interesting functional and structural insights. Here, hydrogen/ deuterium exchange, saturation transfer and differential relaxation ex periments have been performed on oriented lipid bilayer-bound polypept ide samples to measure the exchange lifetimes. The polypeptide, gramic idin 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 sit es are not base catalyzed, consistent with the exclusion of anions fro m this channel. Furthermore, the recently described [1] orientational distribution of the individual peptide carbonyls (i.e. carbonyls eithe r tipped slightly in toward or away from the channel axis) is consiste nt with the observed difference in odd- and even-numbered amide residu e exchange lifetimes.