Conformational studies on analogues of the invertebrate peptide pyroGlu-Asp-Pro-Phe-Leu-Arg-Phe-NH2 using 1H NMR

Abstract

The peptide pQDPFLRFamide is one of several closely related heptapeptides found in invertebrates, including molluscs. Electrophysiological findings and ligand binding studies have both suggested that these heptapeptides probably interact with receptors distinct from those that are activated by the related tetrapeptide FMRFamide (also found in the same group of invertebrates), despite the fact that some synthetic N-terminally extended analogues of the latter show marked tetrapeptide-like activity. We have carried out structural studies, using 1- and 2-dimensional ¹H NMR, on pQDPFLRFamide and some synthetic analogues in which Asp-2 was replaced by Asn and Pro-3 by either Aib (α-amino isobutyric acid) or by Gly. The results are consistent with the suggestion that pQDPFLRFamide can adopt a bent conformation, which might form the basis of the selectivity of this and related heptapeptides.