The putative ancestral peptide of the adipokinetic/red-pigment-concentrating hormone family isolated and sequenced from a dragonfly

Abstract

A neuropeptide with adipokinetic activity in Locusta migratoria and hypertrehalosaemic activity in Periplaneta americana was purified by reversed-phase high performance liquid chromatography from the corpus cardiacum of the dragonfly, Libellula auripennis. After brief enzymatic digestion by 5-oxoprolyl-peptidase the primary structure of the peptide was determined by pulsed-liquid phase sequencing employing Edman degradation. As the peptide was not cleaved by carboxypeptidase the C-terminus was blocked, too. The peptide was assigned as a blocked uncharged octapeptide: Glu-Val-Asn-Phe-Thr-Pro-Ser-TrpNH2. The synthetic peptide was chromatographically indistinguishable from the natural compound and, upon injection in low quantities into dragonflies, elicited mainly haemolymph lipids. Therefore it is called dragonfly adipokinetic hormone (Lia-AKH). It is a new member of the large AKH/RPCH family of peptides. Because of its structural features and its origin from a very primitive insect order it is assumed to represent the putative ancestral peptide of this family. Synthesis was shown to occur in the corpus cardiacum by in vitro incorporation of tritium-labelled Trp into Lia-AKH.