The solution structures of the first and second transmembrane-spanning segments of band 3

We have studied the structures of synthetic peptides which correspond to the proposed first and second membrane-spanning segments of the human red cell anion transporter (band 3). The peptides, which were acetylated at their N-termini and amidated at the C-termini, comprise the 20 amino acids of residues 405-424 and 21 amino acids of residues 436-456 of the human band 3 sequence. The solution structures of the peptides in trifluoroethanol were studied by two-dimensional NMR spectroscopy. Characteristic NOEs were observed indicating that the peptides adopted a predominantly alpha-helical structure in trifluoroethanol solution. Dynamical simulated annealing using the program XPLOR was employed for the structure calculations. The amide exchange rates in trifluoroethanol have also been measured and are consistent with an alpha-helical structure for the peptides.