AN NMR, CD, MOLECULAR-DYNAMICS, AND FLUOROMETRIC STUDY OF THE CONFORMATION OF THE BRADYKININ ANTAGONIST B-9340 IN WATER AND IN AQUEOUS MICELLAR SOLUTIONS

A detailed NMR, CD, fluorometry, and molecular modeling study of a nov el bradykinin antagonist B-9340, containing a novel amino acid D-Igl ( alpha-(2-indanyl)glycine) at position 7, was carried out. The sequence of B-9340 is yp(3)-Gly(4)-Thi(5)-Ser(6)-D-Igl(7)-Oic(8)-Arg(9), where Hyp is hydroxyproline, Thi is beta-(2-thienyl)alanine, and Oic is (3a S,7aS)-octahydroindole-2-carboxylic acid. The CD results exhibit a str iking effect of SDS on the spectrum of the BK antagonist, indicating t hat interaction with the surfactant induces a folded peptide structure . The interaction of this antagonist with phosphatidylinositol was mon itored by fluorometry, indicating that the interaction of the peptide with the lipid is cooperative, and gives a Hill coefficient of 2.3. Th e two-dimensional proton NMR measurements indicate that B-9340 has no stable secondary structure in water solution and contains about 10-15% cis peptide bonds arising from Pro(2), Hyp(3), and Oic(8). In SDS mic elles, NMR reveals the existence of two beta-turns based on a number o f medium-range connectivities that were useful for molecular modeling. The actual molecular modeling and dynamic runs were performed on B-93 40 in an environment consisting of a layer of octyl sulfate anions and water. The results indicate that the structure of B-9340 in a micella r environment is characterized by a nonideal PII-turn comprising resid ues Pro(2) to Thi(5), a nonideal beta II'-turn comprising residues Ser (6)-Arg(9), and broad folding in the middle part of the molecule. The structure is stabilized by several hydrogen bonds and by a salt bridge between the guanidine moiety of Arg(1) and the carboxyl group of Arg( 9), whereas the middle part of the peptide is buried in the micelle. T he structure is deposited as Brookhaven PDB file 1 BDK.