Probing the topological arrangement of the N- and C-terminal residues of bradykinin for agonist activity at the B1 receptor

The conformational features of H-Lys-Arg-Ado-Ser-Pro-Phe-OH (Ado = 12-amino dodecanoic acid), a des-Arg(9) analogue of Lys-bradykinin, have been determ ined by high-resolution NMR in the presence of a zwitterionic lipid environ ment. The analogue is the most active member of a series of analogues desig ned to probe the topological arrangement of the N- and C-termini required f or agonistic activity at the B1 kinin receptor. A novel computational proce dure for the utilization of NOE constraints from cis and trans configuratio nal isomers is illustrated. Only with this computational methodology could the structural features of the N-terminus of the peptide be determined. Usi ng radical-induced relaxation of the H-1 NMR signals, we measured the topol ogical. orientation of the peptide with respect to the zwitterionic lipid i nterface. The results indicate that the long, alkyl chain of the Ado amino acid imbeds into the lipid surface. The structural features of the C-termin us of the B1-selective analogue consist of a well-defined turn. Although re moved from a standard beta-turn, required for activity at the B2 kinin rece ptor, the topological orientation of the side chains of the des-Arg(9) comp ound are surprisingly similar to those previously observed for P-turn-conta ining bradykinin analogues. Therefore, we attribute the high B1 receptor se lectivity, observed upon removal of Arg(9) from bradykinin, solely to the l oss of a charged amino acid and not to altered structural features.