Structure of the transmembrane dimer interface of glycophorin A in membrane bilayers

The hydrophobic transmembsane domain of glycophorin A contains a sequence m otif that mediates dimerization in membrane environments. Long-range interh elical distance measurements using magic angle-spinning NMR spectroscopy pr ovide high-resolution structural constraints on the packing of the dimer in terface in membrane bilayers. We show that direct packing contacts occur be tween glycine residues at positions 79 and 83 in the transmembrane sequence . Additional interhelical constraints between Ile76 and Gly79 and between V al80 and Gly83 restrict the rotational orientation and crossing angle of th e interacting helices. These results refine our previously proposed structu re of the glycophorin A dimer [Smith, S. O., and Bormann, B. J. (1995) Proc . Natl. Acad. Sci. U.S.A. 92, 488-491] which revealed that the methyl group s of Val80 and Val84 are packed against Gly79 and Gly83, respectively.