Structure and orientation of the transmembrane domain of glycophorin A in lipid bilayers.

Rotational resonance (RR) NMR, circular dichroism (CD), and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy are used to establish the secondary structure and orientation of peptides corresponding to the transmembrane domain of human glycophorin A in dimyristoylphosphatidylcholine bilayers. An amide I vibrational frequency of 1650 cm-1 and negative CD absorption bands at 208 and 222 nm indicate that the peptide is largely alpha-helical, while an order parameter of 0.35-0.50 in the ATR-FTIR measurements indicates that the peptide orientation is generally perpendicular to the bilayer plane. High-resolution structural data on the glycophorin A transmembrane (GPA-TM) peptides were obtained by measuring the rate of magnetization exchange between pairs of specific 13C labels using RR NMR. The exchange rates are translated into internuclear distances with a resolution on the order of 0.3 A. These experiments are similar in design to previous experiments on crystalline peptides where the 13C labels were incorporated into amino acids separated by 2-3 residues in the peptide sequence but close together in space due to a helical peptide geometry [Peersen, O.B., Yoshimura, S., Hojo, H., Aimoto, S., & Smith, S.O. (1992) J. Am. Chem. Soc. 114, 4332-4335]. In the GPA-TM peptides, magnetization exchange rates measured between [1-13C]V80 and [2-13C] G83 between [1-13C]M81 and [2-13C]G83 in the middle of the transmembrane sequence correspond to internuclear distances of approximately 4.5 A and are consistent with a helical peptide structure.(ABSTRACT TRUNCATED AT 250 WORDS)