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-m ediated adenylate cyclase activity [Munch, G., Dees, C., Hekman, M., & Palm, D. (1991) Eur. J. Biochem. 198, 357-364]. Circular dichroism an d two-dimensional H-1 NMR techniques were used to investigate the thre e-dimensional structure of the peptide in trifluoroethanol, phospholip id micelles, and small unilamellar phospholipid vesicles. The prepared vesicles were tested for size distribution and stability by using ele ctron microscopy, photon correlation spectroscopy, and P-31 NMR spectr oscopy. The peptide T345-359 adopted a predominantly alpha-helical con formation in either trifluoroethanol or phospholipid micelles and vesi cles. No structural differences were found for the conformation of the peptide in the presence of phospholipid micelles or vesicles, respect ively, using 2D H-1 NMR techniques, suggesting a unique conformation o f T345-359 when associated with model membranes. A computer-aided mode l of the micelle-associated peptide was derived. The relevance of the 3D structure of the intracellular loops of receptors to communicate wi th the G protein in the signal transduction cascade is discussed.