Calcium-binding properties and molecular organization of bradykinin - A solution H-1-NMR study

The NMR features of bradykinin were investigated in dimethylsulfoxide conta ining 1% water. The temperature dependence of chemical shifts and ROESY map s were monitored for the major species where all X-Pro bonds are trans. The occurrence of a head-to-tail ionic interaction and intramolecular hydrogen bends stabilizing a pseudo cyclic arrangement was inferred, a beta turn at the C-terminus being the main feature of the secondary structure. Calcium was shown to bind to the peptide with a dissociation constant K-d = 2.8 +/- 0.2 mM. (2)Pro and (3)Pro carbonyls, as well as the (9)Arg carboxyl, were assigned as the metal-binding sites. A molecular model of the 1 : 1 metal-c omplex was obtained. In light of conformational changes experienced by the peptide upon interaction with calcium, a role for the metal was hypothesize d in the process of conformational selection from the free to the receptor- bound state of bradykinin.