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Determination of helix-helix interactions in membranes by rotational resonance NMR.

Dimerization of human glycophorin A in erythrocyte membranes is mediated by specific interactions within the helical transmembrane domain of the protein. Rotational resonance NMR provides a unique approach for obtaining high-resolution structural data in membrane systems and has been used to establish intermolecular contacts in the glycophorin A dimer by using hydrophobic peptides that correspond to the transmembrane sequence. Magnetization exchange rates were measured between [13C]methyl labels in the hydrophobic sequence -G79-V80-M81-A82-G83-V84- located in the middle of the transmembrane domain and specific [13C]carbonyl labels along the peptide backbone across the dimer interface. Significant magnetization exchange was observed only between V80 (13CH3) and G79 (13C = O) and between V84 (13CH3) and G83 (13C = O), indicating that these residues are packed in the dimer interface in a "ridges-ingrooves" arrangement.