1H-NMR studies of [Sar1]angiotensin II conformation by nuclear Overhauser effect spectroscopy in the rotating frame (ROESY): clustering of the aromatic rings in dimethylsulfoxide

The conformational properties of the octapeptide Sar1]ANG II in dimethylsulfoxide-d6 were investigated by rotating frame nuclear Overhauser effect spectroscopy (ROESY). Interresidue ROESY interactions were observed between Tyr ortho and Phe ring protons, between Phe ring and Pro C gamma protons, and also between His C alpha and Pro C delta protons. A weak connectivity was also observed between the Sar N-CH3 protons and a Tyr ortho proton. Intraresidue interactions between alpha and beta protons in Tyr, His and Phe indicated restricted rotation for the side-chains of the three aromatic residues. These findings suggest that Sar1]ANG II takes up a folded conformation in DMSO in which the three aromatic rings form a cluster. Connectivities between the His C alpha proton and the two Pro C delta protons illustrated a preferred conformation for angiotensin II in DMSO in which the His-Pro bond exists as the trans isomer. The NMR spectroscopic evidence is consistent with the presence of a Tyr charge relay system in the biologically active conformation of angiotensin II and with the postulated role of the Tyr hydroxyl group in angiotensin II for receptor activation.