A TRANSMEMBRANE HELIX DIMER - STRUCTURE AND IMPLICATIONS

The three-dimensional structure of the dimeric transmembrane domain of glycophorin A (GpA) was determined by solution nuclear magnetic reson ance spectroscopy of a 40-residue peptide solubilized in aqueous deter gent micelles. The GpA membrane-spanning alpha helices cross at an ang le of -40 degrees and form a small but well-packed interface that lack s intermonomer hydrogen bonds. The structure provides an explanation f or the previously characterized sequence dependence of GpA dimerizatio n and demonstrates that van der Waals interactions alone can mediate s table and specific associations between transmembrane helices.