Structure, localization and potential role of a novel molluscan trypsin inhibitor in Lymnaea

Neuropeptide Localization in Lymnaea stagnalis: From the Central Nervous System to Subcellular Compartments

Due to the relatively small number of neurons (few tens of thousands), the well-established multipurpose model organism Lymnaea stagnalis, great pond snail, has been extensively used to study the functioning of the nervous system. Unlike the more complex brains of higher organisms, L. stagnalis has a relatively simple central nervous system (CNS) with well-defined circuits (e.g., feeding, locomotion, learning, and memory) and identified individual neurons (e.g., cerebral giant cell, CGC), which generate behavioral patterns. Accumulating information from electrophysiological experiments maps the network of neuronal connections and the neuronal circuits responsible for basic life functions. Chemical signaling between synaptic-coupled neurons is underpinned by neurotransmitters and neuropeptides. This review looks at the rapidly expanding contributions of mass spectrometry (MS) to neuropeptide discovery and identification at different granularity of CNS organization. Abundances and distributions of neuropeptides in the whole CNS, eleven interconnected ganglia, neuronal clusters, single neurons, and subcellular compartments are captured by MS imaging and single cell analysis techniques. Combining neuropeptide expression and electrophysiological data, and aided by genomic and transcriptomic information, the molecular basis of CNS-controlled biological functions is increasingly revealed.

Non-digestible proteins and protease inhibitors: implications for defense of the colored eggs of the freshwater apple snailPomacea canaliculata

Apple snails (Pomacea Perry, 1810) are successful invaders that cause ecological perturbations, economic losses, and medical issues. A peculiar trait of this snail is a high biological potential, related to the absence of predators of their eggs. Eggs show protease inhibitor (PI) activity, originally ascribed to PcOvo perivitellin in the apple snail Pomacea canaliculata (Lamarck, 1822) but absent in PmPV1, the orthologoue of PcOvo, in eggs of the apple snail Pomacea maculata Perry, 1810. As egg fluid diminishes rat growth rate, an antidigestive effect, similar to plant defenses against herbivory, was hypothesized. However, PI activity has not been characterized in apple snail eggs. Here we identify and partially characterize P. canaliculata egg PI and improve our knowledge of the quaternary structure and evolution of PcOvo. Through N-terminal, transcriptomic or proteomic sequencing, and biochemical validation, we identified a Kunitz-type and a Kazal-type inhibitor that, though at low concentration in the egg, exhibit strong PI activity against trypsin, chymotrypsin, elastase, and subtilisin. Additionally, we report three new subunits for the non-digestible storage protein PcOvo. They are likely products of ancient gene duplication, as their sequences exhibit moderate similarity (30%). To our knowledge, this is the first report of Kazal-type inhibition among invertebrate eggs. Inhibiting varied proteases, PI seems an efficient adaptive trait that limits predator’s capacity to digest egg nutrients.

Apple Snail Perivitellin Precursor Properties Help Explain Predators' Feeding Behavior

In contrast with vitellogenin maturation, it is unknown whether gastropod perivitellin precursors are subject to large structural changes. The gastropod reproductive tract includes an accessory organ, the albumen gland (AG), that produces and secretes perivitelline fluid. In the apple snail Pomacea canaliculata, the large, reddish-pink AG provides eggs with perivitellins that are defensive against predators. Although the AG makes a considerable contribution to apple snail biomass, field observations indicate that it is rejected by avian and mammalian predators, although the underlying reason remains unknown. By analyzing the structure-function properties of P. canaliculata perivitellin precursors, we provide insight into perivitellin maturation and its relationship with apple snail predator feeding behavior. Structural analysis using small-angle X-ray scattering, absorption and fluorescence spectroscopy, circular dichroism, electrophoresis, chromatography, and partial proteolysis showed that the size, shape, and structure of perivitellin precursors resemble those of egg mature forms. Functional analysis indicates that the precursors of the defensive perivitellins ovorubin (PcOvo) and perivitellin-2 (PcPV2) are highly stable and antinutritive, withstanding proteinase digestion and displaying structural stability of their quaternary structure under a wide pH range (4.0-10.0). Furthermore, AG extracts limit a predator's ability to digest nutrients and are toxic to mice (median lethal concentration 96 h after administration: 5.9 mg/kg). Treated mice displayed neurologic signs similar to those produced by egg PcPV2. Results indicate that apple snails store active precursors of egg proteins inside the AG, providing evidence that gastropod perivitellin precursors do not experience the large structural processing of invertebrate vitellogenin maturation. These defensive proteins provide the apple snail AG with neurotoxic, antinutritive, and antidigestive activity, a likely explanation for the predators' feeding behavior.

Mortality Caused by Bath Exposure of Zebrafish (Danio rerio) Larvae to Nervous Necrosis Virus Is Limited to the Fourth Day Postfertilization

Nervous necrosis virus (NNV) is a member of the Betanodavirus genus that causes fatal diseases in over 40 species of fish worldwide. Mortality among NNV-infected fish larvae is almost 100%. In order to elucidate the mechanisms responsible for the susceptibility of fish larvae to NNV, we exposed zebrafish larvae to NNV by bath immersion at 2, 4, 6, and 8 days postfertilization (dpf). Here, we demonstrate that developing zebrafish embryos are resistant to NNV at 2 dpf due to the protection afforded by the egg chorion and, to a lesser extent, by the perivitelline fluid. The zebrafish larvae succumbed to NNV infection during a narrow time window around the 4th dpf, while 6- and 8-day-old larvae were much less sensitive, with mortalities of 24% and 28%, respectively.

T-type channels become highly permeable to sodium ions using an alternative extracellular turret region (S5-P) outside the selectivity filter

T-type (Cav3) channels are categorized as calcium channels, but invertebrate ones can be highly sodium-selective channels. We illustrate that the snail LCav3 T-type channel becomes highly sodium-permeable through exon splicing of an extracellular turret and descending helix in domain II of the four-domain Cav3 channel. Highly sodium-permeable T-type channels are generated without altering the invariant ring of charged residues in the selectivity filter that governs calcium selectivity in calcium channels. The highly sodium-permeant T-type channel expresses in the brain and is the only splice isoform expressed in the snail heart. This unique splicing of turret residues offers T-type channels a capacity to serve as a pacemaking sodium current in the primitive heart and brain in lieu of Nav1-type sodium channels and to substitute for voltage-gated sodium channels lacking in many invertebrates. T-type channels would also contribute substantially to sodium leak conductances at rest in invertebrates because of their large window currents.

Tri-domain bifunctional inhibitor of metallocarboxypeptidases A and serine proteases isolated from marine annelid Sabellastarte magnifica

This study describes a novel bifunctional metallocarboxypeptidase and serine protease inhibitor (SmCI) isolated from the tentacle crown of the annelid Sabellastarte magnifica. SmCI is a 165-residue glycoprotein with a molecular mass of 19.69 kDa (mass spectrometry) and 18 cysteine residues forming nine disulfide bonds. Its cDNA was cloned and sequenced by RT-PCR and nested PCR using degenerated oligonucleotides. Employing this information along with data derived from automatic Edman degradation of peptide fragments, the SmCI sequence was fully characterized, indicating the presence of three bovine pancreatic trypsin inhibitor/Kunitz domains and its high homology with other Kunitz serine protease inhibitors. Enzyme kinetics and structural analyses revealed SmCI to be an inhibitor of human and bovine pancreatic metallocarboxypeptidases of the A-type (but not B-type), with nanomolar K(i) values. SmCI is also capable of inhibiting bovine pancreatic trypsin, chymotrypsin, and porcine pancreatic elastase in varying measures. When the inhibitor and its nonglycosylated form (SmCI N23A mutant) were overproduced recombinantly in a Pichia pastoris system, they displayed the dual inhibitory properties of the natural form. Similarly, two bi-domain forms of the inhibitor (recombinant rSmCI D1-D2 and rSmCI D2-D3) as well as its C-terminal domain (rSmCI-D3) were also overproduced. Of these fragments, only the rSmCI D1-D2 bi-domain retained inhibition of metallocarboxypeptidase A but only partially, indicating that the whole tri-domain structure is required for such capability in full. SmCI is the first proteinaceous inhibitor of metallocarboxypeptidases able to act as well on another mechanistic class of proteases (serine-type) and is the first of this kind identified in nature.

The role of the proteinase inhibitor ovorubin in apple snail eggs resembles plant embryo defense against predation

BACKGROUND

Fieldwork has thoroughly established that most eggs are intensely predated. Among the few exceptions are the aerial egg clutches from the aquatic snail Pomacea canaliculata which have virtually no predators. Its defenses are advertised by the pigmented ovorubin perivitellin providing a conspicuous reddish coloration. The nature of the defense however, was not clear, except for a screening for defenses that identified a neurotoxic perivitellin with lethal effect on rodents. Ovorubin is a proteinase inhibitor (PI) whose role to protect against pathogens was taken for granted, according to the prevailing assumption. Through biochemical, biophysical and feeding experiments we studied the proteinase inhibitor function of ovorubin in egg defenses.

METHODOLOGY/PRINCIPAL FINDINGS

Mass spectrometry sequencing indicated ovorubin belongs to the Kunitz-type serine proteinase inhibitor family. It specifically binds trypsin as determined by small angle X-ray scattering (SAXS) and cross-linking studies but, in contrast to the classical assumption, it does not prevent bacterial growth. Ovorubin was found extremely resistant to in vitro gastrointestinal proteolysis. Moreover feeding studies showed that ovorubin ingestion diminishes growth rate in rats indicating that this highly stable PI is capable of surviving passage through the gastrointestinal tract in a biologically active form.

CONCLUSIONS

To our knowledge, this is the first direct evidence of the interaction of an egg PI with a digestive protease of potential predators, limiting predator's ability to digest egg nutrients. This role has not been reported in the animal kingdom but it is similar to plant defenses against herbivory. Further, this would be the only defense model with no trade-offs between conspicuousness and noxiousness by encoding into the same molecule both the aposematic warning signal and an antinutritive/antidigestive defense. These defenses, combined with a neurotoxin and probably unpalatable factors would explain the near absence of predators, opening new perspectives in the study of the evolution and ecology of egg defensive strategies.

Identification of protein components of egg masses indicates parental investment in immunoprotection of offspring by Biomphalaria glabrata (gastropoda, mollusca)

The macromolecules contributed by the freshwater gastropod Biomphalaria glabrata, intermediate host of Schistosoma mansoni, to developing offspring inside egg masses are poorly known. SDS-PAGE fractionated egg mass fluids (EMF) of M line and BB02 B. glabrata were analyzed by MALDI-TOF (MS and tandem MS). A MASCOT database was assembled with EST data from B. glabrata and other molluscs to aid in sequence characterization. Of approximately 20 major EMF polypeptides, 16 were identified as defense-related, including protease inhibitors, a hemocyanin-like factor and tyrosinase (each with possible phenoloxidase activity), extracellular Cu-Zn SOD, two categories of C-type lectins, Gram-negative bacteria-binding protein (GNBP), aplysianin/achacin-like protein, as well as versions of lipopolysaccharide binding protein/bacterial permeability-increasing proteins (LBP/BPI) that differed from those previously described from hemocytes. Along with two sequences that were encoded by "unknown" ESTs, EMF also yielded a compound containing a vWF domain that is likely involved in defense and a polypeptide with homology to the Aplysia pheromone temptin. Further study of B. glabrata pheromones is warranted as these could be useful in efforts to control these schistosome-transmitting snails. Several of the EMF polypeptides were contained in the albumen gland, the organ that produces most EMF. Thus, parental investment of B. glabrata in immunoprotection of its offspring is indicated to be considerable.

Long-term proteasome dysfunction in the mouse brain by expression of aberrant ubiquitin

Many neurodegenerative diseases are characterized by deposits of ubiquitinated and aberrant proteins, suggesting a failure of the ubiquitin-proteasome system (UPS). The aberrant ubiquitin UBB(+1) is one of the ubiquitinated proteins accumulating in tauopathies such as Alzheimer's disease (AD) and polyglutamine diseases such as Huntington's disease. We have generated UBB(+1) transgenic mouse lines with post-natal neuronal expression of UBB(+1), resulting in increased levels of ubiquitinated proteins in the cortex. Moreover, by proteomic analysis, we identified expression changes in proteins involved in energy metabolism or organization of the cytoskeleton. These changes show a striking resemblance to the proteomic profiles of both AD brain and several AD mouse models. Moreover, UBB(+1) transgenic mice show a deficit in contextual memory in both water maze and fear conditioning paradigms. Although UBB(+1) partially inhibits the UPS in the cortex, these mice do not have an overt neurological phenotype. These mouse models do not replicate the full spectrum of AD-related changes, yet provide a tool to understand how the UPS is involved in AD pathological changes and in memory formation.

In vivo release of the antimicrobial peptide hLF1-11 from calcium phosphate cement

We studied the release of human lactoferrin 1-11 (hLF1-11), a potent antimicrobial peptide, in an animal model. Calcium phosphate cement with 50 mg/g hLF1-11 was injected into the femoral canal of 12 rabbits. One, 3, and 7 days later, four animals were terminated, and the femora excised. Sections of bone and cement were removed for histological analysis. We used liquid chromatography-mass spectrometry/mass spectrometry for semiquantitative determination of the hLF1-11 concentration. Blood samples were drawn for leukocyte count and differentiation to identify a potential immunomodulating effect of hLF1-11. After an initial burst release, the hLF1-11 concentration in cement and bone decreased steadily. This in vivo release profile is consistent with earlier in vitro studies. Tissue ingrowth into the cement, without signs of inflammation or necrosis, was observed. Leukocytosis or a shift in leukocyte differentiation did not occur. The carrier released over 99% of the hLF1-11, resulting in peak concentrations at the cement-bone interface. This indicates that hLF1-11 could become a valuable prophylactic agent in osteomyelitis treatment.

Purification and partial characterization of human neutrophil elastase inhibitors from the marine snail Cenchritis muricatus (Mollusca)

Human neutrophil elastase inhibition was detected in a crude extract of the marine snail Cenchritis muricatus (Gastropoda, Mollusca). This inhibitory activity remained after heating this extract at 60 degrees C for 30 min. From this extract, three human neutrophil elastase inhibitors (designated CmPI-I, CmPI-II and CmPI-III) were purified by affinity and reversed-phase chromatographies. Homogeneity of CmPI-I and CmPI-II was confirmed, while CmPI-III showed a single peak in reversed-phase chromatography, but heterogeneity in SDS-PAGE with preliminary molecular masses in the range of 18.4 to 22.0 kDa. In contrast, MALDI-TOF mass spectrometry of CmPI-I and CmPI-II showed that these inhibitors are molecules of low molecular mass, 5576 and 5469 Da, respectively. N-terminal amino acid sequences of CmPI-I (6 amino acids) and CmPI-II (20 amino acids) were determined. Homology to Kazal-type protease inhibitors was preliminarily detected for CmPI-II. Both inhibitors, CmPI-I and CmPI-II are able to inhibit human neutrophil elastase strongly, with equilibrium dissociation constant (Ki) values of 54.2 and 1.6 nM, respectively. In addition, trypsin and pancreatic elastase were also inhibited, but not plasma kallikrein or thrombin. CmPI-I and CmPI-II are the first human neutrophil elastase inhibitors described in a mollusk.

Endocrine disruption in aquatic pulmonate molluscs: few evidences, many challenges

As compared to other groups of aquatic gastropods, documented examples of endocrine disruption in pulmonates are rather limited. This is quite surprising because the endocrine control of physiological functions has been extensively studied in these animals. In the model-species Lymnaea stagnalis, the neurohormonal regulation of reproduction has been thoroughly investigated, and the primary structure of several peptides and receptors involved in endocrine processes has been established. However, the use of this knowledge has been fairly limited in the context of ecotoxicology, to investigate the effects of endocrine-disrupting chemicals. The present review summarizes the main and more recent findings on the neuroendocrine control of reproduction in aquatic pulmonate snails (Basommatophora). It then comprehensively describes selected in vivo laboratory and semi-field studies which provide evidence for possible endocrine disrupting effects of estrogenic and androgenic test compounds [e.g., ethynylestradiol, methyltestosterone (MT)], and of environmental contaminants [e.g., cadmium (Cd), tributyltin (TBT), and nonylphenol (NP), pesticides]. Finally, challenging perspectives for future research are discussed.

Binding of salivary agglutinin to IgA

SAG (salivary agglutinin), which is identical to gp-340 (glycoprotein-340) from the lung, is encoded by DMBT1 (deleted in malignant brain tumours 1). It is a member of the SRCR (scavenger receptor cysteine-rich) superfamily and contains 14 SRCR domains, 13 of which are highly similar. SAG in saliva is partially complexed with IgA, which may be necessary for bacterial binding. The goal of the present study was to characterize the binding of purified SAG to IgA. SAG binds to a variety of proteins, including serum and secretory IgA, alkaline phosphatase-conjugated IgGs originating from rabbit, goat, swine and mouse, and lactoferrin and albumin. Binding of IgA to SAG is calcium dependent and is inhibited by 0.5 M KCl, suggesting that electrostatic interactions are involved. Binding of IgA was destroyed after reduction of SAG, suggesting that the protein moiety is involved in binding. To pinpoint further the binding domain for IgA on SAG, a number of consensus-based peptides of the SRCR domains and SRCR interspersed domains were designed and synthesized. ELISA binding studies with IgA indicated that only one of the peptides tested, comprising amino acids 18-33 (QGRVEVLYRGSWGTVC) of the 109-amino-acid SRCR domain, exhibited binding to IgA. This domain is identical to the domain of SAG that is involved in binding to bacteria. Despite this similar binding site, IgA did not inhibit binding of Streptococcus mutans to SAG or peptide. These results show that the binding of IgA to SAG is specifically mediated by a peptide sequence on the SRCR domains.

Bacteria Binding by DMBT1/SAG/gp-340 Is Confined to the VEVLXXXXW Motif in Its Scavenger Receptor Cysteine-rich Domains

The scavenger receptor cysteine-rich (SRCR) proteins form an archaic group of metazoan proteins characterized by the presence of SRCR domains. These proteins are classified in group A and B based on the number of conserved cysteine residues in their SRCR domains, i.e. six for group A and eight for group B. The protein DMBT1 (deleted in malignant brain tumors 1), which is identical to salivary agglutinin and lung gp-340, belongs to the group B SRCR proteins and is considered to be involved in tumor suppression and host defense by pathogen binding. In a previous study we used nonoverlapping synthetic peptides covering the SRCR consensus sequence to identify a 16-amino acid bacteria-binding protein loop (peptide SRCRP2; QGRVEVLYRGSWGTVC) within the SRCR domains. In this study, using overlapping peptides, we pinpointed the minimal bacteria-binding site on SRCRP2, and thus DMBT1, to an 11-amino acid motif (DMBT1 pathogen-binding site 1 or DMBT1pbs1; GRVEVLYRGSW). An alanine substitution scan revealed that VEVL and Trp are critical residues in this motif. Bacteria binding by DMBT1pbs1 was different from the bacteria binding by the macrophage receptor MARCO in which an RXR motif was critical. In addition, the homologous consensus sequences of a number of SRCR proteins were synthesized and tested for bacteria binding. Only consensus sequences of DMBT1 orthologues bound bacteria by this motif.

A peptide domain of bovine milk lactoferrin inhibits the interaction between streptococcal surface protein antigen and a salivary agglutinin peptide domain

The peptide domain of salivary agglutinin responsible for its interaction with cell surface protein antigen (PAc) of Streptococcus mutans or bovine lactoferrin was found in the same peptide, scavenger receptor cysteine-rich domain peptide 2 (SRCRP2). Inhibition studies suggest that PAc and lactoferrin, of which residues 480 to 492 seem important, competitively bind to the SRCRP2 domain of salivary agglutinin.

Purification and preliminary characterization of a plasma kallikrein inhibitor isolated from sea hares Aplysia dactylomela Rang, 1828

An inhibitor active against pancreatic trypsin was found in the crude extract from the sea hares Aplysia dactylomelaRang, 1828. A stronger inhibitory activity against human plasma kallikrein was detectable after treating this extract at 60 degrees C, for 30 min. The plasma kallikrein inhibitor (AdKI) purification was achieved by acetone fractionation (80%) v/v, ion-exchange chromatography on Mono Q column and gel filtration chromatography on Superdex 75 column (FPLC system). By the latter a molecular mass of 2900 Da was estimated. The purified inhibitor strongly inhibits human plasma kallikrein with a K(i) value of 2.2 x 10(-10)M, while human plasmin and pancreatic trypsin were inhibited with K(i) values of 1.8 x 10(-9) and 4.7 x 10(-9)M, respectively. Chymotrypsin, pancreatic elastase, pancreatic kallikrein and thrombin are not inhibited. The effect of AdKI on plasma kallikrein was confirmed by the prolongation of activated partial thromboplastin time, using a clotting time assay. The inhibitor did not affect prothrombin time or thrombin time. AdKi is a more specific inhibitor than other serine proteinase inhibitors from marine invertebrates.

Proteomics Analysis of Rat Brain Postsynaptic Density

The postsynaptic density contains multiple protein complexes that together relay the presynaptic neurotransmitter input to the activation of the postsynaptic neuron. In the present study we took two independent proteome approaches for the characterization of the protein complement of the postsynaptic density, namely 1) two-dimensional gel electrophoresis separation of proteins in conjunction with mass spectrometry to identify the tryptic peptides of the protein spots and 2) isolation of the trypsin-digested sample that was labeled with isotope-coded affinity tag, followed by liquid chromatography-tandem mass spectrometry for the partial separation and identification of the peptides, respectively. Functional grouping of the identified proteins indicates that the postsynaptic density is a structurally and functionally complex organelle that may be involved in a broad range of synaptic activities. These proteins include the receptors and ion channels for glutamate neurotransmission, proteins for maintenance and modulation of synaptic architecture, sorting and trafficking of membrane proteins, generation of anaerobic energy, scaffolding and signaling, local protein synthesis, and correct protein folding and breakdown of synaptic proteins. Together, these results imply that the postsynaptic density may have the ability to function (semi-) autonomously and may direct various cellular functions in order to integrate synaptic physiology.

Proteomics as a tool for the investigation of seafood and other marine products

The state-of-the-art and future trends of the application of proteomics to seafood and other marine products are reviewed. Consumers' demands for seafood products have increased in the recent years and this situation has underlined the need to guarantee the safety, traceability, authenticity, and health benefits of such products. The increasing presence of commercially available aquaculture products has also prompted the seafood industry to face newer challenges. In this sense, a review of the present status and perspectives of the application of proteomics in the development of newer biotechnology products of marine origin is given.

Long-term culture of decapsulated gastropod embryos: a transplantation study

Encapsulated embryos of the pond snail Helisoma trivolvis have been useful for examining neural development and neural circuit function during development. However, their full potential in developmental studies is limited by the lack of an effective method for long-term culture of decapsulated embryos. In the present study, decapsulated early embryos were either cultivated ex ovo in various media under different environmental conditions or transplanted into host egg capsules. Although diluted capsular fluid, 30% M199, and albumen-gland-conditioned medium were partially effective in promoting embryonic growth for a short time, none of the media promoted normal embryonic development in long-term tests. In contrast, after previously decapsulated and experimentally manipulated embryos were transplanted into host capsules, their growth and development were similar to their intact siblings. In combination with laser ablation, this transplantation technique was used to demonstrate the role played by a pair of serotonergic neurons in regulating an embryonic rotational behavior. These results suggest that embryonic transplantation is an extremely effective technique for achieving long-term growth and development of previously decapsulated embryos and therefore can be instrumental in investigating cell lineage, function, and development in encapsulated embryos.

Identification of the bacteria-binding peptide domain on salivary agglutinin (gp-340/DMBT1), a member of the scavenger receptor cysteine-rich superfamily

Salivary agglutinin is encoded by DMBT1 and identical to gp-340, a member of the scavenger receptor cysteine-rich (SRCR) superfamily. Salivary agglutinin/DMBT1 is known for its Streptococcus mutans agglutinating properties. This 300-400 kDa glycoprotein is composed of conserved peptide motifs: 14 SRCR domains that are separated by SRCR-interspersed domains (SIDs), 2 CUB (C1r/C1s Uegf Bmp1) domains, and a zona pellucida domain. We have searched for the peptide domains of agglutinin/DMBT1 responsible for bacteria binding. Digestion with endoproteinase Lys-C resulted in a protein fragment containing exclusively SRCR and SID domains that binds to S. mutans. To define more closely the S. mutans-binding domain, consensus-based peptides of the SRCR domains and SIDs were designed and synthesized. Only one of the SRCR peptides, designated SRCRP2, and none of the SID peptides bound to S. mutans. Strikingly, this peptide was also able to induce agglutination of S. mutans and a number of other bacteria. The repeated presence of this peptide in the native molecule endows agglutinin/DMBT1 with a general bacterial binding feature with a multivalent character. Moreover, our studies demonstrate for the first time that the polymorphic SRCR domains of salivary agglutinin/DMBT1 mediate ligand interactions.

Protein synthesis in synaptosomes: a proteomics analysis

A proteomics approach was used to identify the translation products of a unique synaptic model system, squid optic lobe synaptosomes. Unlike its vertebrate counterparts, this preparation is largely free of perikaryal cell fragments and consists predominantly of pre-synaptic terminals derived from retinal photoreceptor neurones. We metabolically labelled synaptosomes with [(35)S] methionine and applied two-dimensional gel electrophoresis to resolve newly synthesized proteins at high resolution. Autoradiographs of blotted two-dimensional gels revealed de novo synthesis of about 80 different proteins, 18 of which could be matched to silver-stained gels that were run in parallel. In-gel digestion of the matched spots and mass spectrometric analyses revealed the identities of various cytosolic enzymes, cytoskeletal proteins, molecular chaperones and nuclear-encoded mitochondrial proteins. A number of novel proteins (i.e. not matching with database sequences) were also detected. In situ hybridization was employed to confirm the presence of mRNA and rRNA in synaptosomes. Together, our data show that pre-synaptic endings of squid photoreceptor neurones actively synthesize a wide variety of proteins involved in synaptic functioning, such as transmitter recycling, energy supply and synaptic architecture.