Conformational diversity of T-kinin in DMSO, water and HFA.

T-kinin (Ile-Ser-BK) is related to BK in its biological profile, but unlike BK, is more resistant to the action of ACE. A detailed NMR and molecular modeling study of T-kinin has been carried out in three diverse media: water (pH 4.0), DMSO-d(6) and HFA solution. In DMSO-d(6), T-kinin adopts a structure with two tandem beta-turns: the first at the mid segment tetrad Pro(4)-Pro(5)-Gly(6)-Phe(7) (type I) and the C-terminal end Ser(8)-Pro(9)-Phe(10)-Arg(11) harbors the second turn (also type I). While the first beta-turn is lost in presence of water, the second persists. In HFA, NMR reveals a alpha-helix like structure spanning residues Arg(3) to Arg(11). Structures with cis peptide bonds (XX-Pro) have been observed for T-kinin in DMSO-d(6) but not in water and HFA. Differences in the structures of BK and T-kinin in water may explain their susceptibility/resistance to the action of ACE.