Abstract
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.
Highlights
Peptides occur in the whole animal kingdom, from the least evolved phyla with a very simple nervous system to the highest vertebrates
All predicted peptide precursors meet with following criteria: (i) each putative peptide precursor is less than 500 amino acids in length and has a signal peptide; (ii) each precursor contains one or several putative peptides that are flanked by conventional cleavage sites
Prolactin and growth hormone are two distinct neuropeptide hormones that have been found in all vertebrate groups but not in cyclostomes [27], prolactinergic neurons that were detected immunochemically occur in a protochordate [28]
Summary
Peptides occur in the whole animal kingdom, from the least evolved phyla with a very simple nervous system (coelenterates) to the highest vertebrates. In recent studies of Baggerman et al [10,11,12], the peptidome (the battery of all present peptides) of the larval Drosophila central nervous system was analysed at the amino acid sequence level by means of nanoscale liquid chromatography combined by tandem mass spectrometry and database mining. These results provided biochemical evidence for the expression of not less than 40 peptides in the Drosophila brain at a specific time point. In this study we describe a new in silico searching program that employs typical hallmarks of biological peptides and their precursors, which are not used by the currently available predictive algorithms
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