Conformation of a beta-adrenoceptor-derived signal transducing peptide as inferred by circular dichroism and H-1 NMR spectroscopy

The peptide T345-359 representing the fourth intracellular loop of the avian beta-adrenoceptor has been shown to strongly inhibit receptor-mediated adenylate cyclase activity [Munch, G., Dees, C., Hekman, M., & Palm, D. (1991) Eur. J. Biochem. 198, 357-364]. Circular dichroism and two-dimensional H-1 NMR techniques were used to investigate the three-dimensional structure of the peptide in trifluoroethanol, phospholipid micelles, and small unilamellar phospholipid vesicles. The prepared vesicles were tested for size distribution and stability by using electron microscopy, photon correlation spectroscopy, and P-31 NMR spectroscopy. The peptide T345-359 adopted a predominantly alpha-helical conformation in either trifluoroethanol or phospholipid micelles and vesicles. No structural differences were found for the conformation of the peptide in the presence of phospholipid micelles or vesicles, respectively, using 2D H-1 NMR techniques, suggesting a unique conformation of T345-359 when associated with model membranes. A computer-aided model of the micelle-associated peptide was derived. The relevance of the 3D structure of the intracellular loops of receptors to communicate with the G protein in the signal transduction cascade is discussed.