Characterization of a functionally expressed dipeptidyl aminopeptidase III from Drosophila melanogaster

Abstract

A Drosophila melanogaster cDNA clone (GH01916) encoding a putative 723-residue long (82 kDa) protein (CG 7415) and displaying 50% identity with mammalian cytosolic dipeptidyl aminopeptidase (DPP) III was functionally expressed in Schneider S 2 cells. Immunocytochemical studies using anti-(rat liver DPP III) Ig indicated the expression of this putative DPP III at the outer cell membrane and into the cytosol of transfected cells. Two protein bands (82 and 86 kDa) were immunologically detected after PAGE and Western blot of cytosol or membrane prepared from transfected cells. Western blot analysis of partially purified D. melanogaster DPP III confirmed the overexpression of these two protein bands into the cytosol and on the membranes of transfected cells. Despite the identification of six potential glycosylation sites, PAGE showed that these protein bands were not shifted after deglycosylation experiments. The partially purified enzyme hydrolysed the insect myotropic neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) at the Tyr-Leu bond (K m 4 lM). In addition, low concentration of the specific DPP III inhibitor tynorphin prevented proctolin degradation (IC 50 ¼ 0.62 ± 0.15 lM). These results constitute the first characterization of an evolutionarily conserved insect DPP III that is expressed as a cytosolic and a membrane peptidase involved in proctolin degradation.Keywords: enkephalinase; genome sequencing; insects; neuropeptides; proctolin.Mammalian DPP III was first discovered in the bovine anterior pituitary gland [1] and it has been recently cloned from rat liver as a 738-residue (82 kDa) cytosolic protein [2,3]. This enzyme (EC 3.4.14.4) is a zinc metallopeptidase containing a specific domain HELLGH-18X-E where a zinc molecule is bound to both histidines [4]. DPP III is mainly identified as a cytosolic peptidase, but DPP III was also detected on membranes prepared from the brain of guineapig [5] and rat [6]. Angiotensins and enkephalins constitute the preferred substrates of the rat brain cytosolic DPP III [7]. The routes of degradation of the insect myotropic neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) have been compared to those of enkephalins. Indeed, a dipeptidyl aminopeptidase activity appears as one major proctolindegrading peptidase, liberating the N-terminal Arg-Tyr dipeptide [8][9][10][11]. This dipeptidyl aminopeptidase activity was compared to the vertebrate DPP III [11] and is mainly recovered as a cytosolic enzyme [8]. Interestingly, a proctolin-degrading DPP activity is also measured on membranes [8,9] especially those obtained from insect proctolin-rich tissues such as hindgut [10]. None of the presumed proctolinases has been fully characterized yet.We recently purified [12] from hindgut membranes of the cockroach, Blaberus craniifer, a proctolin-degrading protein (76 and 80 kDa) that removes the N-terminal dipeptide from proctolin (K m ¼ 3.8 ± 1.1 lM) and enkephalins (K m ¼ 4.2 ± 0.8 lM). The partial sequencing of this purified protein revealed a significant homology with the rat liver cytosolic ...

Multiple mechanisms limit the duration of wakefulness in Drosophila brain

“…Also involved in synaptic transmission and downregulated by sleep deprivation is the synaptic vesicle protein AP-47 (50,81). Neuropeptide mechanisms of synaptic transmission may also be affected since CG7415, which encodes a protein predicted to process neuropeptides (54), has reduced expression with sleep deprivation.…”

Novel Therapeutic Role for Dipeptidyl Peptidase III in the Treatment of Hypertension

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Entropy-driven binding of opioid peptides induces a large domain motion in human dipeptidyl peptidase III

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