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.
