Peptide profiling of a single Locusta migratoria corpus cardiacum by nano-LC tandem mass spectrometry

Signature-Ion-Triggered Mass Spectrometry Approach Enabled Discovery of N- and O-Linked Glycosylated Neuropeptides in the Crustacean Nervous System

Crustaceans are commonly used model organisms to study neuromodulation. Despite numerous reported crustacean neuropeptide families and their functions, there has been no report on neuropeptide glycosylation. This is in part due to a lack of sensitive methods that enable deciphering this intricate low-abundance post-translational modification, even though glycosylation has been shown to play an important role in neuromodulation. Here, we describe the discovery of glycosylated neuropeptides with an enrichment-free approach, taking advantage of signature oxonium ions produced in higher-energy collision dissociation (HCD) MS/MS spectra. The detection of the oxonium ions in the HCD scans suggests glycan attachment to peptides, allowing electron-transfer/higher-energy collision dissociation (EThcD) to be performed to selectively elucidate structural information of glycosylated neuropeptides that are buried in nonglycosylated peptides. Overall, 4 N-linked and 14 O-linked glycosylated neuropeptides have been identified for the first time in the crustacean nervous system. In addition, 91 novel putative neuropeptides have been discovered based on the collected HCD scans. This hybrid approach, coupling a shotgun method for neuropeptide discovery and targeted strategy for glycosylation characterization, enables the first report on glycosylated neuropeptides in crustaceans and the discovery of additional neuropeptides simultaneously. The elucidation of novel glycosylated neuropeptides sheds light on the crustacean peptidome and offers novel insights into future neuropeptide functional studies.

Purification and identification of angiotensin I-converting enzyme-inhibitory peptides from apalbumin 2 during simulated gastrointestinal digestion

BACKGROUND

Bee larvae are considered to be an important reservoir for proteins. However, little attention has been paid to the release of potential bioactive peptides from bee larva proteins. In this study the major protein in bee larvae was hydrolyzed in vitro by gastrointestinal enzymes. The peptide profile of the hydrolysis was characterized by gel filtration chromatography and tricine-SDS-PAGE. Furthermore, the bioactive peptide was isolated and identified by Q-TOF-MS/MS.

RESULTS

The major bee larva protein was identified as apalbumin 2 and was more digestible into peptides with molecular weights lower than 3 kDa. The hydrolysate obtained after 3 h of digestion exhibited angiotensin I-converting enzyme (ACE)-inhibitory activity and was purified sequentially by gel filtration and RP-HPLC. The molecular weights of peptide fractions with ACE-inhibitory activity were distributed between 0.5 and 1.5 kDa. A novel peptide with highest ACE-inhibitory activity (IC50 54.9 µmol L(-1) ) was purified by further RP-HPLC. The amino acid sequence of this peptide was identified as LLKPY (632.40 Da).

CONCLUSION

ACE-inhibitory peptides could be formed from bee larvae through gastrointestinal digestion. The most active peptide (LLKPY) is potentially useful as a therapeutic agent in treating hypertension.

Isolation, identification and synthesis of four novel antioxidant peptides from rice residue protein hydrolyzed by multiple proteases

Multiple proteases were optimized to hydrolyze the rice residue protein (RRP) to produce novel antioxidant peptides. An antioxidant peptide fraction (RRPB3) with IC50 of 0.25 mg/ml was purified from the RRP hydrolysate using membrane ultrafiltration followed by size exclusion chromatography and reversed-phase FPLC. RRPB3 was found to include four peptides (RRPB3 I-IV) and their amino acid sequences were RPNYTDA (835.9 Da), TSQLLSDQ (891.0 Da), TRTGDPFF (940.0 Da) and NFHPQ (641.7 Da), respectively. Furthermore, four peptides were chemically synthesized and their antioxidant activities were assessed by DPPH radical scavenging, ABTS radical scavenging assay and FRAP-Fe(3+) reducing assay, respectively. Both RRPB3 I and III showed synergistic antioxidant activity compared to each of them used alone. All four synthetic peptides showed excellent stability against simulated gastrointestinal proteases. Therefore, the peptides isolated from RRP may be used as potential antioxidants in the food and drug industries.

Direct MALDI-TOF mass spectrometric peptide profiling of neuroendocrine tissue of Drosophila

Direct MALDI-TOF mass spectrometric peptide profiling is increasingly used to analyze the peptide complement in the nervous system of a variety of invertebrate animals, from leech to Aplysia and many arthropod species, especially insects and crustaceans. Proper sample preparation is often the most crucial step to obtain the necessary data. Here, we describe protocols for the use of MALDI-TOF mass spectrometry to directly analyze the peptidome of neuroendocrine tissues of insects, particularly Drosophila melanogaster, by MALDI-TOF MS.

MALDI-TOF mass spectrometry approaches to the characterisation of insect neuropeptides

The diversity of insect neuropeptides coupled with the limitations from the small size of the insects themselves combine to make positive identification through peptide sequencing a highly challenging task. The advent of the "soft-ionisation" techniques of MALDI-TOF and electrospray (ESI)-Q-TOF mass spectrometry, coupled with the additional information from insect genome projects have revolutionised the characterisation of insect neuropeptides, such that sequences can now be obtained from just a few cells, where before thousands of insects had to be laboriously dissected, extracted and purified. Some of the procedures that are now used to identify these peptides are described here. Once the neuropeptides have been identified, it then becomes possible to use this knowledge to define physiological functionality.

Identification of myotropic neuropeptides from the brain and corpus cardiacum-corpus allatum complex of the beetle, Zophobas atratus

The neuropeptide profiles of the two major neuro-endocrinological organs, brain and retrocerebral complex corpus cardiacum-corpus allatum (CC/CA) of adult beetles, Zophobas atratus Fabricius (Coleoptera:Tenebrionidae) were analyzed by a combination of high performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time of flight tandem mass spectrometry (MALDI TOF/TOF MS). The homological semi-isolated heart bioassay was used to screen HPLC fractions for myotropic activity in tissues, revealing several cardiostimulatory and cardioinhibitory factors from both the brain and CC/CA. Analysis of HPLC fractions by MALDI-TOF MS identified seven mass ions that could be assigned to other known peptides: leucomyosuppressin (LMS), Tribolium castaneum pyrokinin 2, sulfakinin 1, myoinhibitory peptide 4, a truncated NVP-like peptide, Tenebrio molitor AKH and crustacean cardioactive peptide. In addition, two novel peptides, myosuppressin (pEDVEHVFLRFa), which differs from LMS by one amino acid (E for D at position 4) and pyrokinin-like peptide (LPHYTPRLa) were also identified. To establish cardioactive properties of some of the identified peptides, chemical synthesis was carried out and their activities were tested using the heart bioassay.

The roles of Dippu-allatostatin in the modulation of hormone release in Locusta migratoria

Dippu-allatostatins (ASTs) have pleiotropic effects in Locusta migratoria. Dippu-ASTs act as releasing factors for adipokinetic hormone I (AKH I) from the corpus cardiacum (CC) and also alter juvenile hormone (JH) biosynthesis and release from the corpus allatum (CA). Dippu-AST-like immunoreactivity is found within lateral neurosecretory cells (LNCs) of the brain and axons within the paired nervi corporis cardiaci II (NCC II) to the CC and the CA, where there are extensive processes and nerve endings over both of these neuroendocrine organs. There was co-localization of Dippu-AST-like and proctolin-like immunoreactivity within these regions. Dippu-ASTs increase the release of AKH I in a dose-dependent manner, with thresholds below 10(-11)M (Dippu-AST 7) and between 10(-13) and 10(-12)M (Dippu-AST 2). Both proctolin and Dippu-AST 2 caused an increase in the cAMP content of the glandular lobe of the CC. Dippu-AST 2 also altered the release of JH from the locust CA, but this effect depended on the concentration of peptide and the basal release rates of the CA. These physiological effects for Dippu-ASTs in Locusta have not been shown previously.

Inter-phyla studies on neuropeptides: the potential for broad-spectrum anthelmintic and/or endectocide discovery

Flatworm, nematode and arthropod parasites have proven their ability to develop resistance to currently available chemotherapeutics. The heavy reliance on chemotherapy and the ability of target species to develop resistance has prompted the search for novel drug targets. In view of its importance to parasite/pest survival, the neuromusculature of parasitic helminths and pest arthropod species remains an attractive target for the discovery of novel endectocide targets. Exploitation of the neuropeptidergic system in helminths and arthropods has been hampered by a limited understanding of the functional roles of individual peptides and the structure of endogenous targets, such as receptors. Basic research into these systems has the potential to facilitate target characterization and its offshoots (screen development and drug identification). Of particular interest to parasitologists is the fact that selected neuropeptide families are common to metazoan pest species (nematodes, platyhelminths and arthropods) and fulfil specific roles in the modulation of muscle function in each of the three phyla. This article reviews the inter-phyla activity of two peptide families, the FMRFamide-like peptides and allatostatins, on motor function in helminths and arthropods and discusses the potential of neuropeptide signalling as a target system that could uncover novel endectocidal agents.

Peptidomics: identification and quantification of endogenous peptides in neuroendocrine tissues

Neuropeptides perform a large variety of functions as intercellular signaling molecules. While most proteomic studies involve digestion of the proteins with trypsin or other proteases, peptidomics studies usually analyze the native peptide forms. Neuropeptides can be studied by using mass spectrometry for identification and quantitation. In many cases, mass spectrometry provides an understanding of the precise molecular form of the native peptide, including post-translational cleavages and other modifications. Quantitative peptidomics studies generally use differential isotopic tags to label two sets of extracted peptides, as done with proteomic studies, except that the Cys-based reagents typically used for quantitation of proteins are not suitable because most peptides lack Cys residues. Instead, a number of amine-specific labels have been created and some of these are useful for peptide quantitation by mass spectrometry. In this review, peptidomics techniques are discussed along with the major findings of many recent studies and future directions for the field.

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.

Functional Screening of Serine Protease Inhibitors in the Medical Leech Hirudo medicinalis Monitored by Intensity Fading MALDI-TOF MS

The blood-feeding invertebrates are a rich biological source of drugs and lead compounds to treat cardiovascular diseases because they have evolved highly efficient mechanisms to feed on their hosts by blocking blood coagulation. In this work, we focused our attention on the leech Hirudo medicinalis. We performed, by "intensity fading" MALDI-TOF mass spectrometry, a comprehensive detection and functional analysis of pre-existent peptides and small proteins with the capability of binding to trypsin-like proteases related to blood coagulation. Combining "intensity fading MS" and off-line LC prefractionation allowed us to detect more than 75 molecules present in the leech extract that interact specifically with a trypsin-like protease over a sample profile of nearly 2,000 different peptides/proteins in the 2-20-kDa range. Moreover we resolved 232 individual components from the complex mixture, 13 of which have high sequence homology with previously described serine protease inhibitors. Our findings indicate that such extracts are much more complex than expected. Additionally, intensity fading MS, when complemented with LC separation strategies, seems to be a useful tool to investigate complex biological samples, establishing a new bridge between profiling, functional peptidomics, and subsequent drug discovery.

Melatonin-induced neuropeptide release from isolated locust corpora cardiaca

A method, based on a combination of mass spectrometry and liquid chromatography, was developed to investigate the release of neuropeptides from isolated locust corpora cardiaca. Melatonin, octopamine, trehalose and forskolin were administered to the perifused glands. The neuropeptides present in the releasates (spontaneous versus induced) were visualized by either conventional or capillary HPLC. Identification was achieved by means of MALDI-TOF MS and/or nanoflow-LC-Q-TOF MS. The observed effects of these chemicals regarding AKH release were in line with previous studies and validate the method. The most important finding of this study was that administration of melatonin stimulated the release of adipokinetic hormone precursor related peptides (APRP 1 and APRP 2), neuroparsins (NP A1, NP A2 and NP B) and diuretic peptide.