Influence of methylation of the histidine ring of [Sar1]angiotensin II on conformation and biological activity.
[Sar1His(1-Me)6]ANG II and [Sar1His(3-Me)6]ANG II were synthesized by the solid-phase method and purified by reversed-phase HPLC. 1H-NMR spectroscopy at 400 MHz demonstrated the presence of two major conformers for both peptides in DMSO, representing cis and trans isomers (ratio 1:3 and 1:4, respectively) due to restricted rotation at the His-Pro bond. The contractile activities of these peptides in the rat isolated uterus assay were < 0.1 and 27% of that of ANG II, respectively. The bioactivities of these analogues were mirrored in their NMR spectra: the inactive analogue [Sar1His(1-Me)6]ANG II showed perturbations of the Sar and His residues which were not present for [Sar1His(3-Me)6]ANG II and the reference agonist [Sar1]ANG II. The high activity of the analogue methylated at His N3 suggests that an ionizable imidazole proton is not an absolute requirement for expression of biological activity by angiotensin ligands, and that the imidazole group in the molecule may function in an ion dipole-based mechanism when an intramolecular proton transfer (charge relay) mechanism is not available. The biological activity of the ligand appears to depend on the degree of proton transfer from Tyr-OH to the imidazole acceptor, wherein complete (formal) proton transfer represents 100% activity.
Moore
G J
GJ
Department of Pharmacology and Therapeutics, University of Calgary, Health Sciences Centre, Alberta, Canada.
Goghari
M H
MH
Franklin
K J
KJ
D000804:Angiotensin II / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D001681:Biological Assay; D005260:Female; D006639:Histidine / Q000737:chemistry*; D008745:Methylation; D011487:Protein Conformation; D051381:Rats; D013237:Stereoisomerism
D000804:Angiotensin II; D006639:Histidine; C074793:angiotensin II, Sar(1)-