Structural studies of two antiaggregant RGDW peptides by 1H and 13C NMR

The structural features of Arg-Gly-Asp-related sequences have been investigated by 1H and 13C NMR. Two linear peptides which inhibit platelet aggregation with a high efficiency have been studied: D-Arg-Gly-Asp-Trp and L-Arg-Gly-Asp-Trp. Analysis of pH titration effects, amide proton exchange rates and inter-proton distances obtained from ROESY spectra suggest that these small fragments predominantly adopt a type II' beta-turn structure in solution. Folding features of a non-active cyclic peptide based on the same sequence (cyclo-[Arg-Gly-Asp-Trp]2) have also been investigated. The biological relevance of these structures is discussed.