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

Abstract

The conformational properties of the octapeptide [Sar 1]ANG II in dimethylsulfoxide-d 6 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 γ protons, and also between His C α and Pro C δ protons. A weak connectivity was also observed between the Sar N-CH 3 protons and a Tyr ortho proton. Intraresidue interactions between α and β protons in Tyr, His and Phe indicated restricted rotation for the side-chains of the three aromatic residues. These findings suggest that [Sar 1]ANG II takes up a folded conformation in DMSO in which the three aromatic rings form a cluster. Connectivities between the His C α proton and the two Pro C δ 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.