Conformations of Arg-Gly-Asp containing heterodetic cyclic peptides: solution and crystal studies

Abstract

Peptides containing the sequence Arg-Gly-Asp antagonize binding of fibrinogen to its platelet GPIIb/IIIa receptor, thereby inhibiting platelet aggregation. Incorporation of the sequence into cyclic pentapeptide disulfides has been reported to yield effective antagonists. The conformations in solution of two such antagonists, (2-mercaptobenzoy1)-Na-methylArgGly-Asp-2-mercaptoanilide cyclic disulfide (1) and Ac-Cys-Na-methylArg-Gly-A~p-Pen-NH~ cyclic disulfide (2), have been studied using a constrained distance geometry search procedure in conjunction with proton NMR data, and a structure of 1 has been determined from single-crystal X-ray diffraction data. NMR spectra of the cyclic diaryl disulfide 1 at 203 K in methanol show two slowly exchanging conformations. The Arg-Gly-Asp region of the major form is characterized, inter alia, by an extended Gly residue flanked by an Na-methylArg residue in a conformation roughly consistent with the i + 2 position of a &turn and an Asp residue in a C7 like conformation. In the minor component, the Asp residue is near the aR conformation. The bamer to exchange between the two forms is estimated at 11 kcal/mol. NMR data and analysis of the constrained distance geometry search results suggest that, at room temperature in dimethyl sulfoxide-sulfolane, the dominant conformation of the Arg-Gly-Asp regions of both 1 and 2 is like that in the major component of 1 at 203 K. (2-Mercaptobenzoy1)-Na-methylArg-Gly-Asp-2-mercaptoanilide cyclic disulfide (1) was crystallized from aqueous ethanol as a solvated nitrate salt in a cell of dimensions a = 27.919 (16) A, b = 7.552 (3) A, c = 16.3131 (10) A, and j 3 = 108.79 (5)' with four formula units in space group C2. The structure was solved by direct methods and refined to R = 0.057 for 2869 observations (I 2 340). The crystal structure of 1 and the most probable conformation of its minor form in solution agree closely.

Pharmacophore refinement of gpIIb/IIIa antagonists based on comparative studies of antiadhesive cyclic and acyclic RGD peptides

“…This finding is not in agreement with a recently published comparative study of a series of homo-and heterodetic cyclic Arg-Gly-Asp peptides, refined by means of NMR spectroscopy and X-ray crystallography [63,67,68]. In this investigation the authors defined four structurally distinct categories, according to the conformational preference of the recognition tripeptide backbone.…”

What have snakes taught us about integrins?

“…The RGD region was found to be highly flexible, and the side chains of Arg and Asp with positive and negative charges, respectively, are separated by glycine and turned in opposite directions. Based on this information on their steric structure, a series of RGD-and KGD-containing peptides, including cyclic peptides, were designed by computer modelling; some derivatives were found to be as potent as intact kistrin in a platelet aggregation assay [64][65][66][67]. To date, a variety of RGD-and KGD derivatives have been under clinical trials and have been demonstrated to be effective agents in reducing complications of ischemia, especially restenosis after percutaneous transluminal coronary angioplasty (PTCA) [68,69].…”

Modulation of Protein-Protein Interactions by Stabilizing/Mimicking Protein Secondary Structure Elements

“…Scientists at SmithKline Beecham reported on the cyclic RGD-containing disulfide derivative 12, a highly active antagonist of the α IIb β 3 , with crystal and solution structures characterized by an extended conformation at the Gly residue, and C 7 -like conformations in the regions around Arg and Asp residues [69]. To test this conformational features, γ-turn mimetics were incorporated at the Asp level in nonpeptide analogues.…”