Synthesis, characterization, and conformational analysis of the D/L-Tic7 stereoisomers of the bradykinin receptor antagonist D-Arg0[Hyp3,Thi5,D-Tic7,Oic8]bradykinin.
D-Arg0[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (HOE-140) is a potent (Ki = 0.11 nM) inhibitor of [3H]bradykinin binding to bradykinin B2 receptors found on human IMR-90 fetal lung fibroblasts. During the synthesis of this compound, we isolated and unambiguously identified the L-Tic7 stereoisomer (WIN 65365), which exhibits a 2000-fold lower binding affinity (Ki = 130 nM) than HOE-140 to the bradykinin receptor. A similar decrease in potency is observed for WIN 65365 inhibition of bradykinin-stimulated 45Ca2+ efflux from IMR-90 cells. Both HOE-140 and WIN 65365 appear to be competitive antagonists at the IMR-90 bradykinin receptor. This is the first documentation of bradykinin binding and functional antagonist activity by a bradykinin peptide analogue with an L amino acid replacing Pro7. In an attempt to rationalize the differences in binding affinities of HOE-140 and WIN 65365, a conformational analysis of the peptides was undertaken using annealed molecular dynamics (AMD). Conformational analysis of HOE-140 reveals a strong preference for the formation of a type II' beta-turn in the carboxy-terminal region. Analogous modeling of WIN 65365 reveals that its conformation is strikingly different from HOE-140 in that the four carboxy-terminal residues of WIN 65365 do not form a beta-turn. These differences in low-energy conformations between the two peptides may lead to a better understanding of the molecular interaction of antagonists with the bradykinin receptor.
Sawutz
D G
DG
Department of Enzymology, Sterling Winthrop Pharmaceuticals Research Division, Collegeville, Pennsylvania 19426.
Salvino
J M
JM
Seoane
P R
PR
Douty
B D
BD
Houck
W T
WT
Bobko
M A
MA
Doleman
M S
MS
Dolle
R E
RE
Wolfe
H R
HR
D000595:Amino Acid Sequence; D001920:Bradykinin / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors* / Q000138:chemical synthesis / Q000737:chemistry; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D066298:In Vitro Techniques; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D018002:Receptors, Bradykinin / Q000378:metabolism*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D018002:Receptors, Bradykinin; C065679:icatibant; D001920:Bradykinin; D002118:Calcium