The interactions of human angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) with Eu3+, La3+, and Gd3+ are monitored in H2O and D2O by 1H nmr. The peptide forms 1:1 complexes with the trivalent lanthanide ions in which the carboxyl groups of Asp-1 and Phe-8 form the metal binding site. Addition of La3+ induces no significant perturbations in the CαH-NH coupling constants or chemical shifts of the low field resonances of the peptide, indicating that the conformation of the interior residues of the peptide backbone is unchanged upon metal complexation. The addition of Gd3+ induces differential line-broadening of the resonances of the angiotensin II spectrum. These perturbations are discussed qualitatively in terms of the relative distance of each residue from the metal-binding site, and calculations are performed to estimate the absolute metal-proton distances for six of the hydrogens in the hormone (the NH's of Val-2, Tyr-4, Ile-5, His-6, and Phe-8, and the C2-H of the His-6 imidazole). Various literature models for the conformation of the hormone is aqueous solution are discussed in terms of their consistency with these distances.
ASJC Scopus subject areas
- Inorganic Chemistry