The Ac-RGD-NH₂ peptide as a probe of slow conformational exchange of short linear peptides in DMSO

According to general belief, the conformational information on short linear peptides in solution derived at ambient temperature from NMR spectrometry represents a population-weighted average over all members of an ensemble of rapidly interconverting conformations. Usually the search for discrete conformations is concentrated at low temperatures especially when sharp NMR resonances are detected at room temperature. Using the peptide Ac-RGD-NH₂ (Ac-Arg-Gly-Asp-NH₂, Ac: acetyl) as a model system and following a new approach, we have been able to demonstrate that short linear peptides can adopt discrete conformational states in DMSO-d₆ (DMSO: dimethylsulfoxide) which vary in a way critically dependent on the reconstitution conditions used before their dissolution in DMSO-d₆. The conformers are stabilized by intramolecular hydrogen bonds, which persist at high temperatures and undergo a very slow exchange with their extended structures in the NMR chemical shift time scale. The reported findings provide clear evidence for the occurrence of solvent-induced conformational exchange and point to DMSO as a valuable medium for folding studies of short linear peptides.