Studies of the receptor-bound conformation of αIIbβ3 antagonists by 15N-edited NMR spectroscopy

We report the results of NMR studies and computer simulations of potent antagonists reflective of the αIIbβ3 receptor‐bound conformations. The peptides c[Mpa–15N‐Arg1–15N‐Gly2–15N‐Asp3–15N‐Phe4–15N‐Arg5–Cys]‐NH2 (Phe–Arg analog) (Mpa: 3‐mercaptopropionic acid) and c[Mpa–15N‐Arg1–15N‐Gly2–15N‐Asp3–15N‐Asp4–15N‐Val5–Cys]‐NH2 (Asp–Val analog) were subjected to 15N‐edited NMR experiments to study the conformations of these peptides in the absence and in the presence of αIIbβ3 receptor. The NMR studies of the Phe–Arg analog, a selective αIIbβ3 antagonist, resulted in distinctly different experimental data in the presence and absence of the receptor. The computer simulations for this peptide resulted in one large family of structures consistent with the experimental data. This conformation suggests a type I β‐turn spanning residues Arg1 and Gly2 when bound to the receptor and we were able to establish a model for the three dimensional arrangement of the pharmacophores. The studies on the Asp–Val analog, an αvβ3 antagonist that binds to the αIIbβ3 with moderate affinity, resulted in conformations that are not as well defined as those for the Phe–Arg analog but are consistent with the model established for this analog. These results are important for the design of novel αIIbβ3 antagonists. © 2003 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 66: 326–338, 2002