A combined spectroscopic study of the solution conformation of bradykinin

CD, NMR and laser Raman spectroscopy have been used in a complementary fashion to study the conformation of bradykinin and related peptides. The results are interpreted to mean that the secondary structure of bradykinin in aqueous solution is a time average of two interconverting structures - one disordered and the other partially ordered. The peptide evidently spends a maximum of about 20% of its time in the partially ordered conformation which features a hydrogen-bonded structure at the C-terminus, most likely a gamma-turn with Pro7 as the second residue. Bradykinin and its analogs enjoy considerable conformational adaptability in terms of response to changes in temperature and solvent composition. Thus, dioxane favors the hydrogen-bonded structure, while aqueous NaCl0(4) and methanol favor the trans Pro7 isomer. The pronounced CD changes caused by increasing the temperature are attributed to a conformational transition, which is reflected in the CD of the Phe residues and possibly also the Arg-Pro-Pro moiety. The magnitude of the thermodynamic functions for the presumed transition are interpreted to mean that the structure of water plays a dominant role in determining the conformation of the peptide.