Isolation and structural characterization of a novel peptide related to gamma-melanocyte stimulating hormone from the brain of the leech Theromyzon tessulatum

In Silico Identification of New Secretory Peptide Genes in Drosophila melanogaster

Bioactive peptides play critical roles in regulating most biological processes in animals. The elucidation of the amino acid sequence of these regulatory peptides is crucial for our understanding of animal physiology. Most of the (neuro)peptides currently known were identified by purification and subsequent amino acid sequencing. With the entire genome sequence of some animals now available, it has become possible to predict novel putative peptides. In this way, BLAST (Basic Local Alignment Searching Tool) analysis of the Drosophila melanogaster genome has allowed annotation of 36 secretory peptide genes so far. Peptide precursor genes are, however, poorly predicted by this algorithm, thus prompting an alternative approach described here. With the described searching program we scanned the Drosophila genome for predicted proteins with the structural hallmarks of neuropeptide precursors. As a result, 76 additional putative secretory peptide genes were predicted in addition to the 43 annotated ones. These putative (neuro)peptide genes contain conserved motifs reminiscent of known neuropeptides from other animal species. Peptides that display sequence similarities to the mammalian vasopressin, atrial natriuretic peptide, and prolactin precursors and the invertebrate peptides orcokinin, prothoracicotropic hormones, trypsin modulating oostatic factor, and Drosophila immune induced peptides (DIMs) among others were discovered. Our data hence provide further evidence that many neuropeptide genes were already present in the ancestor of Protostomia and Deuterostomia prior to their divergence. This bioinformatic study opens perspectives for the genome-wide analysis of peptide genes in other eukaryotic model organisms.

Discovering new invertebrate neuropeptides using mass spectrometry

Neuropeptides are a complex set of messenger molecules controlling a wide array of regulatory functions and behaviors within an organism. These neuromodulators are cleaved from longer protein molecules and often experience numerous post-translational modifications to achieve their bioactive form. As a result of this complexity, sensitive and versatile analysis schemes are needed to characterize neuropeptides. Mass spectrometry (MS) through a variety of approaches has fueled the discovery of hundreds of neuropeptides in invertebrate species in the last decade. Particularly successful are direct tissue and single neuron analyses by matrix-assisted laser desorption/ionization (MALDI) MS, which has been used to elucidate approximately 440 neuropeptides, and examination of neuronal homogenates by electrospray ionization techniques (ESI), also leading to the characterization of over 450 peptides. Additional MS methods with great promise for the discovery of neuropeptides are MS imaging and large-scale peptidomics studies in combination with a sequenced genome.

A new family of growth and differentiation factors derived from the N-terminal domain of proopiomelanocortin (N-POMC)

There is a large body of in vitro evidence that pituitary function is not only dependent on hormonal signals from the brain but also on paracrine signals produced in the tissue itself. These signals appear to be involved in the control of pituitary hormone secretion as well as in pituitary cell differentiation and development (for review see Denef C. Paracrine mechanisms in the pituitary. In: Imura H, editor. The pituitary gland, 2nd ed. Raven Press, 1994: 351-378; Denef C. Autocrine/paracrine intermediates in hormone action and modulation of cellular responses to hormones. In: Conn M, editor. Handbook of Physiology. New York: Oxford University Press, 1998 (in press)). The paracrine factors which have been identified in the pituitary belong to diverse biological molecules such as neuropeptides, acetylcholine, growth factors, cytokines and posttranslationally modified derivatives of pituitary hormone such as cleaved prolactin (PRL) and the gonadotropin alpha-subunit. Recently, we have identified several N-terminal fragments of the polypeptide proopiomelanocortin (POMC) as a novel family of growth and differentiation factors in the rat anterior pituitary.

Isolation and characterization of a leech neuropeptide in rat brains: coupling to nitric oxide release in leech, rat and human tissues

The osmoregulator peptide (leech osmoregulatory factor, LORF; IPEPYVWD) was first found in the leech central nervous system (CNS). Given the fact that certain peptides can be found in mammals and invertebrates, e.g., opioid, we examined rat brains to determine if LORF was present. This peptide was found and isolated by successive reversed-phase HPLC purification steps and characterized by electrospray mass spectrometry measurement. It was sequenced by Edman degradation and quantified in different tissues by ELISA. Our results demonstrate the presence of LORF in the hypothalamus, thalamus, and striatum (6 pmol/mg of protein extract) and in other brain areas at lower levels. This octapeptide is also present in the rat duodenum and liver (10 to 14 pmol/mg) and at lower levels in heart, lung, pancreas and caudal spinal cord (< 5 pmol/mg). The testes, adrenals and kidneys have the lowest levels of all the tissues examined (ca. 0.5 pmol/mg of protein). Furthermore, we also demonstrate that LORF is coupled to nitric oxide (NO) release in leech CNS, rat hypothalamus and human saphenous vein in a manner which is inhibited by a nitric oxide synthase inhibitor as well as an antibody directed toward LORF. The study demonstrates that LORF, and its function in relation to NO release, has been conserved over more than 400 million years of evolution.

Prodynorphin in invertebrates

We have characterized a prodynorphin-like molecule in an invertebrate, specifically in the rhynchobdellid leech Theromyzon tessulatum. The 14270 Da protein was purified by gel permeation chromatography, anti-leucine-enkephalin-affinity column separation followed by reverse-phase HPLC. Its complete characterization was performed by Edman degradation, enzymatic treatments, and matrix assisted laser-desorption time of flight mass spectrometry. This 119 amino-acid protein exhibits 28.8% sequence identity with rat prodynorphin, 22.9% with human prodynorphin, and 21.8% with the pig molecule. Within the leech precursor, alpha-Neo-endorphin, dynorphin-A, and dynorphin B-like peptides are present at the C-terminus as in vertebrate prodynorphin. These biological active peptides exhibit 100%, 50%, and 76.6% sequence identity with their counterparts in mammals, respectively. The amount of leucine-enkephalin is identical to that found in vertebrates. Leech prodynorphin is distinguished from that found in mammals in that the N-terminus is shorter. This report constitutes the first complete biochemical characterization of a prodynorphin in invertebrates.

A renin-like enzyme in the leech Theromyzon tessulatum

We report on the biochemical isolation and characterization of a 32 kDa aspartyl protease from the leech Theromyzon tessulatum. Following a three step purification (gel permeation chromatography, pepstatin A-sepharose affinity column separation followed by reversed-phase HPLC) a renin-like enzyme was purified to homogeneity. The first 124 amino acid residues of the N-terminal part of the purified S-pyridylethylated leech renin exhibits a 26.5-35.5% sequence identity with that of mammals. The 20-81 region of leech renin exhibits a 80% sequence homology with the 175-232 region in mammals. This highly conserved region, which is also found in all aspartic proteases, possesses the aspartyl catalytic residue (D11TGSS). Leech renin hydrolyses at neutral pH and at 37 degrees C the Leu10-Leu11 bond of synthetic porcine angiotensinogen tetradecapeptide yielding the angiotensin I and the Leu11-Val12-Tyr13-Ser14 peptides, with a specific activity of 115 microg AI/min/mg (K[M] 22 microM; K[cat], 2.7). This hydrolysis is inhibited by pepstatin A (IC50: 4.6 microM). Moreover, this enzyme is found on a multiple hormone precursor of 19 kDa which exhibits a specific activity of 850 pmol AI/min/mg of renin. This is the first biochemical characterization of a renin-like enzyme in invertebrates and non-mammalian vertebrates.

Purification, sequence analysis, and cellular localization of a prodynorphin-derived peptide related to the alpha-neo-endorphin in the rhynchobdellid leech Theromyzon tessulatum

Cells immunoreactive to an antiserum specifically directed against vertebrate alpha-Neo-endorphin (alpha-NE) were detected in the internal wall of anterior and posterior suckers of the rhynchobdellid leech Theromyzon tessulatum. These cells have morphological and ultrastructural characteristics close to the "releasing gland cells" of adhesive organs. The epitope recognized by anti-alpha-NE was contained in granules having a diameter of 0.2-0.3 microm. Previous works involving the brain of this leech demonstrate the existence of approximately 14 neurons immunoreactive to the anti-alpha-NE. Following an extensive purification including high pressure gel permeation and reversed-phase high performance liquid chromatography, epitopes contained in both suckers and central nervous system were isolated. Purity of the isolated peptides was controlled by capillary electrophoresis. Their sequences were determined by a combination of automated Edman degradation, electrospray mass spectrometry measurement, and coelution experiments in reversed-phase high performance liquid chromatography with synthetic alpha-NE. The results demonstrate that epitopes recognized by the anti-alpha-NE in the suckers and the central nervous system are identical to vertebrate alpha-NE (YGGFLRKYPK). This finding constitutes the first biochemical characterization of a prodynorphin-derived peptide in invertebrates. Moreover the isolation of this peptide in the annelida establishes the very ancient phylogenetic origin of alpha-NE as well as its conservation in evolution.

Metabolism of angiotensins by head membranes of the leech Theromyzon tessulatum

Angiotensins (angiotensin I, angiotensin II, angiotensin II-amide) have been isolated in leeches and such peptides are involved in diuresis in these animals. To explore possible inactivation mechanisms of these peptides, angiotensins were incubated with head membranes of the leech T. tessulatum. Membranes derived from head parts of this leech are very rich in peptidases. They contain endopeptidase-24.11-like enzyme (NEP-like) associated with a battery of exopeptidase. The way that angiotensins are degraded by the combined attack of these membrane peptidases has been investigated. The contribution of individual peptidases was assessed by adding inhibitors (phosphoramidon, captopril and amastatin) to the membrane fractions, when they were incubated with the peptides. In the case of angiotensin I, the primary attack was performed by a combined action of the NEP-like and the ACE-like enzymes, followed by aminopeptidase attacks. Angiotensin II and III were hydrolyzed by NEP-like enzyme at the same Tyr-Ile bond, whereas the N-terminal arginine residue of angiotensin III was removed by an arginyl aminopeptidase. These results show that angiotensins are efficiently degraded by membranes and that NEP-like enzyme plays a key role in this process.

Biochemical properties of the angiotensin-converting-like enzyme from the leech Theromyzon tessulatum

This article reports the evidence and the biochemical properties of an angiotensin-converting (ACE)-like enzyme from head parts of the leech Theromyzon tessulatum. After solubilization from membranes with Triton X-114, the ACE-like enzyme was purified from the detergent-poor fraction. Four steps of purification including gel permeation and anion exchange chromatographies followed by a reversed-phase HPLC were needed. This poor glycosylated peptidyl dipeptidase (of ca. 120 kDa) hydrolyzes, at pH 8.4 and at 37 degrees C, the Phe8-His9 bond of angiotensin I with a high catalytic activity (i.e., K(m): 830 microM and Kcat/K(m): 153 s-1 mM-1). The hydrolysis of angiotensin I is inhibitable at 80% by captopril (IC50 = 175 nM) and lisinopril (IC50 = 35 nM). This activity is strictly dependent on the presence of NaCl and is increased by Zn2+. This zinc metallopeptidase also attacks peptides that have in their sequence either Gly-His, Gly-Phe, or Phe-His bond [e.g., enkephalins (Kcat/K(m): 12 s-1 mM-1) or bradykinin (Kcat/K(m): 2200 s-1 mM-1]. Taken together, these arguments are consistent with an ACE-like activity implicated in metabolism of angiotensins and bradykinin in leeches.

Isolation of a neuropeptide-degrading endopeptidase from the leech Theromyzon tessulatum

Extracts of head parts prepared from the leech Theromyzon tessulatum hydrolyse the Gly3-Phe4 bond of synthetic [D-Ala2, Leu5]enkephalin and the Gly-His bond of benzoyl-Gly-His-Leu. The metabolism of benzoyl-Gly-His-Leu was completely inhibited by captopril, consistent with an angiotensin-converting enzyme activity. Such an enzyme has recently been isolated from T. tessulatum. However, the enkephalin hydrolysis by captopril (100 microM) was inhibited to a maximum of 70%. The residual activity hydrolyzing enkephalin was inhibited by phosphoramidon, consistent with the presence of endopeptidase-24.11, a mammalian enzyme implicated in the metabolism of neuropeptides. This enzyme was isolated using four steps of purification including gel-permeation and anion-exchange chromatographies followed by reverse-phase HPLC. This neuropeptide endopeptidase (of approximate molecular mass 45 kDa) hydrolyses, at pH 7 and 37 degrees C, both the Gly3-Phe4 bond of synthetic [D-Ala2, Leu5]enkephalin and the Phe8-His9 bond of angiotensin I. Cleavage of [D-Ala2, Leu5]enkephalin yields, respectively, the Tyr-D-Ala-Gly and Phe-Leu peptides with a specific activity of 29 nmol Tyr-D-Ala-Gly.min-1.mg protein-1 (Km 95 microM). The hydrolysis of angiotensin I yields angiotensin II and the dipeptide His-Leu with a specific activity of 1.2 nmol angiotensin min-1.mg protein-1 (Km 330 microM). The metabolism of these peptides was totally inhibited by phosphoramidon. This study therefore provides biochemical evidence for neuropeptide-degrading endopeptidases in leeches.

Diversity and modulation of ionic conductances in leech neurons

A complete understanding of animal behavior at the cellular level requires detailed information on the intrinsic biophysical properties of neurons, muscles, and the synaptic connections they make. In the past 10 to 15 years, electrophysiological studies of leech neurons have revealed a diverse array of voltage-gated ionic conductances distinguished by their pharmacological sensitivity to classic ion channel blockers. Voltage-clamp studies have provided new information about the kinetics and voltage-dependence of Na+ conductances, several K+ currents, including IA, IK and IK(Ca.), and high- and low-voltage-gated Ca2+ conductances. These studies showed that the action potentials of most leech neurons result from the usual sequence of permeability changes to Na+, K+, and Ca2+ ions. They also added insight as to the role played by particular combinations of conductances in providing individual neurons with electrical properties appropriate for the particular information they encode. Evidence is accumulating on the modulatory actions fo endogenous neurotransmitters such as FMRFamide, serotonin, and octopamine on motor behaviors in the animal. Parallel studies suggest that changes in behavior can be explained, at least in part, by the alteration of firing patterns of selected neurons and muscles resulting from modulation of multiple ion conductances. This makes the leech exceptionally attractive for neuroethological studies because it is one of the simplest organisms in which the methods of psychology and neurobiology can be combined. Information gathered from this animal will therefore increase our understanding regarding general principles underlying the cellular basis of behavior.

A comparison of the leech Theromyzon tessulatum angiotensin I-like molecule with forms of vertebrate angiotensinogens: a hormonal system conserved in the course of evolution

After five steps of purification including gel permeation, anti-angiotensin I affinity column chromatography followed by reverse-phase HPLC, a peptide immunoreactive to two different antisera (anti-angiotensin II and anti-angiotensin I) was purified to homogeneity from extracts of the leech Theromyzon tessulatum. The first 14 amino acid residues of the purified peptide (DRVYIHPFHLLXWG) established by automated Edman degradation, reveal the existence in leeches of an angiotensin I-like molecule close to human angiotensin I. The sequence of the purified peptide presents 78.5% of homology with the N-terminal part of human angiotensinogen. Moreover, in its sequence, this peptide presents the cleavage sites of vertebrate angiotensin metabolic enzymes, i.e. the renin and the angiotensin-converting enzyme. This finding constitutes the first biochemical characterization of an angiotensin I in Invertebrates. It also reflects the high conservation of angiotensins in the course of evolution, suggesting a fundamental role of this family in fluid homeostasis.

Isolation and structural characterization of enkephalins in the brain of the rhynchobdellid leech Theromyzon tessulatum

This paper reports the purification of four peptides related to enkephalins from the brain of the leech Theromyzon tessulatum. After reverse-phase HPLC purification, the sequence of the enkephalins (YGGFM, YGGFL, FM, FL) was established by a combination of automated Edman degradation, electrospray mass spectrometry measurement, and co-elution experiments in reverse-phase HPLC with synthetic peptides. ELISA titrations performed on each purified peptide indicated that the major amount was borne by the leucine-enkephalin. The ratio of leucine-enkephalin and methionine-enkephalin of 2:1 is in line with previous immunocytochemical data obtained on T. tessulatum brains. The presence of enkephalins in T. tessulatum, an animal belonging to the oldest group of coelomate metazoans (the Annelida) establishes the very ancient phylogenetic origin of opioids and their conservation in the course of evolution.

Isolation of a renin-like enzyme from the leech Theromyzon tessulatum

This article reports the purification of a renin-like enzyme (an aspartyl protease) from head parts of the leech Theromyzon tessulatum. After four steps of purification including gel permeation and anion exchange chromatographies followed by reversed-phase HPLC, this enzyme was purified to homogeneity. The renin-like enzyme (of 32 kDa) hydrolyses at neutral pH and at 37 degrees C, the Leu10-Leu11 bond of synthetic porcine angiotensinogen tetradecapeptide yielding the angiotensin I and the Leu11-Val12-Tyr13-Ser14 peptide as products, with a specific activity of 1.35 pmol AI/min/mg (Km 22 microM; Kcat 2.7). The hydrolysis of angiotensinogen is inhibitable at 90% by pepstatin A (IC50 = 4.6 microM), consistent with a renin activity. This is the first biochemical evidence of renin-like enzyme in invertebrates.