Head-to head comparison of mGlu1 and mGlu5 receptor activation in chronic treatment of absence epilepsy in WAG/Rij rats

Acute treatment with positive allosteric modulators (PAMs) of mGlu1 and mGlu5 metabotropic glutamate receptors (RO0711401 and VU0360172, respectively) reduces the incidence of spike-and wave discharges in the WAG/Rij rat model of absence epilepsy. However, from the therapeutic standpoint, it was important to establish whether tolerance developed to the action of these drugs. We administered either VU0360172 (3 mg/kg, s.c.) or RO0711401 (10 mg/kg, s.c.) to WAG/Rij rats twice daily for ten days. VU0360172 maintained its activity during the treatment, whereas rats developed tolerance to RO0711401 since the 3rd day of treatment and were still refractory to the drug two days after treatment withdrawal. In response to VU0360172, expression of mGlu5 receptors increased in the thalamus of WAG/Rij rats after 1 day of treatment, and remained elevated afterwards. VU0360172 also enhanced mGlu5 receptor expression in the cortex after 8 days of treatment without changing the expression of mGlu1a receptors. Treatment with RO0711401 enhanced the expression of both mGlu1a and mGlu5 receptors in the thalamus and cortex of WAG/Rij rats after 3-8 days of treatment. These data were different from those obtained in non-epileptic rats, in which repeated injections of RO0711401 and VU0360172 down-regulated the expression of mGlu1a and mGlu5 receptors. Levels of VU0360172 in the thalamus and cortex remained unaltered during the treatment, whereas levels of RO0711401 were reduced in the cortex at day 8 of treatment. These findings suggest that mGlu5 receptor PAMs are potential candidates for the treatment of absence epilepsy in humans.

Gene variants with suicidal risk in a sample of subjects with chronic migraine and affective temperamental dysregulation

BACKGROUND

Risk factors for suicide are at least partially heritable and functional polymorphisms of targeted genes have been suggested to be implicated in the pathogenesis of this phenomenon. However, other studies examining the association between specific gene variants and suicide revealed inconsistent findings. We aims to evaluate the possible association between MAO-A3, CYP1A2*1F and GNB3 gene variants, hopelessness and suicidal risk in a sample of subjects with chronic migraine and affective temperamental dysregulation.

METHODS

56 women were genotyped for MAO-A3, CYP1A2*1F and GNB3 gene variants. Participants were also assessed using Beck Hopelessness Scale (BHS), the Temperament Evaluation of the Memphis, Pisa, Paris and San Diego-Autoquestionnaire (TEMPS-A), and the Suicidal History Self-Rating Screening Scale (SHSS).

RESULTS

Patients with higher total scores on affective dysregulated temperaments are more likely to have higher BHS (11.27+/=5.54 vs. 5.73+/=3.81; t19.20 = -3.57; p < 0.01) and higher SHSS total scores (4.79+/=3.31 vs. 1.05±2.31; t17.74 = -3.90; p < 0.001) than those with lower total scores. 67% of patients in the dysregulated group has BHS total scores >= 9 indicating high levels of hopelessness. No association was found between MAO-A3, CYP1A2*1F and GNB3 gene variants and suicidal risk as assessed by BHS and SHSS.

CONCLUSIONS

This study did not sustain the association between MAO-A3, CYP1A2*1F and GNB3 gene variants and increased suicidal risk in patients with chronic migraine and affective temperamental dysregulation. Further studies investigating the gene-environment interaction or focusing on other genetic risk factors involved in suicidal behaviour are needed.  

Cinnabarinic acid, an endogenous metabolite of the kynurenine pathway, activates type 4 metabotropic glutamate receptors

Cinnabarinic acid is an endogenous metabolite of the kynurenine pathway that meets the structural requirements to interact with glutamate receptors. We found that cinnabarinic acid acts as a partial agonist of type 4 metabotropic glutamate (mGlu4) receptors, with no activity at other mGlu receptor subtypes. We also tested the activity of cinnabarinic acid on native mGlu4 receptors by examining 1) the inhibition of cAMP formation in cultured cerebellar granule cells; 2) protection against excitotoxic neuronal death in mixed cultures of cortical cells; and 3) protection against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity in mice after local infusion into the external globus pallidus. In all these models, cinnabarinic acid behaved similarly to conventional mGlu4 receptor agonists, and, at least in cultured neurons, the action of low concentrations of cinnabarinic acid was largely attenuated by genetic deletion of mGlu4 receptors. However, high concentrations of cinnabarinic acid were still active in the absence of mGlu4 receptors, suggesting that the compound may have off-target effects. Mutagenesis and molecular modeling experiments showed that cinnabarinic acid acts as an orthosteric agonist interacting with residues of the glutamate binding pocket of mGlu4. Accordingly, cinnabarinic acid did not activate truncated mGlu4 receptors lacking the N-terminal Venus-flytrap domain, as opposed to the mGlu4 receptor enhancer, N-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxamide (PHCCC). Finally, we could detect endogenous cinnabarinic acid in brain tissue and peripheral organs by high-performance liquid chromatography-tandem mass spectrometry analysis. Levels increased substantially during inflammation induced by lipopolysaccharide. We conclude that cinnabarinic acid is a novel endogenous orthosteric agonist of mGlu4 receptors endowed with neuroprotective activity.

Proteomic profiles in hyperandrogenic syndromes

BACKGROUND

Polycystic ovary syndrome (PCOS) and congenital adrenal hyperplasia (CAH) represent the most common causes of hyperandrogenism. Although the etiopathogeneses of these syndromes are different, they share many clinical and biochemical signs, such as hirsutism, acne, and chronic anovulation. Experimental data have shown that peripheral T-lymphocytes function as molecular sensors, being able to record molecular signals either at staminal and mature cell levels, or hormones at systemic levels.

METHODS

Twenty PCOS women and 10 CAH with 21-hydroxylase deficiency, aged between 18-35 yr, were studied. T-cells purified from all patients and 20 healthy donors have been analyzed by 2-dimensional gel electrophoresis. Silver-stained proteomic map of each patient was compared with a control map obtained by pooling protein samples of the 20 healthy subjects.

RESULTS

Spots of interest were identified by peptide mass fingerprint. Computer analysis evidenced several peptidic spots significantly modulated in all patients examined. Some proteins were modulated in both syndromes, others only in PCOS or in CAH. These proteins are involved in many physiological processes as the functional state of immune system, the regulation of the cytoskeleton structure, the oxidative stress, the coagulation process, and the insulin resistance.

CONCLUSION

Identification of the physiological function of these proteins could help to understand ethiopathogenetic mechanisms of hyperandrogenic syndromes and its complications.

Modulation of proteomic profile in H295R adrenocortical cell line induced by mitotane

Mitotane, 1,1-dichloro-2-(o-chlorophenyl)-2-(p-chloro-phenyl) ethane (o,p'-DDD), is a compound that represents the effective agent in the treatment of the adrenocortical carcinoma (ACC), able to block cortisol synthesis. In this type of cancer, the biological mechanism induced by this treatment remains still unknown. In this study, we have already shown a greater impairment in the first steps of the steroidogenesis and recognized a little effect on cell cycle. We also evaluated the variation of proteomic profile of the H295R ACC cell line, either in total cell extract or in mitochondria-enriched fraction after treatment with mitotane. In total cell extracts, triose phosphate isomerase, alpha-enolase, D-3-phosphoglycerate dehydrogenase, peroxiredoxin II and VI, heat shock protein 27, prohibitin, histidine triad nucleotide-binding protein, and profilin-1 showed a different expression. In the mitochondrial fraction, the following proteins appeared to be down regulated: aldolase A, peroxiredoxin I, heterogenous nuclear ribonucleoprotein A2/B1, tubulin-beta isoform II, heat shock cognate 71 kDa protein, and nucleotide diphosphate kinase, whereas adrenodoxin reductase, cathepsin D, and heat shock 70 kDa protein 1A were positively up-regulated. This study represents the first proteomic study on the mitotane effects on ACC. It permits to identify some protein classes affected by the drug involved in energetic metabolism, stress response, cytoskeleton structure, and tumorigenesis.

Proteomic analysis of peripheral T lymphocytes, suitable circulating biosensors of strictly related diseases

T lymphocytes and/or their subpopulations from peripheral blood may represent molecular sensors to be used for the evaluation of gene expression modification in physiological and pathological conditions, providing a unique and easily available biological model for integrated studies of gene expression in humans. In this study, a proteomic approach was applied to evaluate the association between changes in T cell protein expression patterns and specific diseased conditions. In particular, two hyperandrogenic syndromes were studied, sharing many clinical and biochemical signs: polycystic ovary syndrome (PCOS) and congenital adrenal hyperplasia (CAH). Comparison of proteomic maps of T lymphocytes derived from patients affected by PCOS or CAH with those derived from healthy subjects showed that 14 proteins are expressed differentially in both PCOS and CAH, 15 exclusively in PCOS and 35 exclusively in CAH. Seventeen of these proteins have been identified by mass spectrometry analysis. Furthermore, proteomic data mining by hierarchical clustering was performed, highlighting T lymphocytes competence as a living biosensor system.

Alpha-defensin increase in peripheral blood mononuclear cells from patients with hepatitis C virus chronic infection

The alpha-defensin genes promoter regions contain a putative nuclear factors of activated T cells (NFAT)-binding site and it is known that hepatitis C virus (HCV) core protein activates the interleukin (IL)-2 gene transcription through the NFAT pathway. The aims of this study were to investigate if HCV affects the alpha-defensin expression in peripheral human mononuclear cells (PBMCs) and to evaluate the existence of a correlation between alpha-defensins and liver damage in patients with chronic hepatitis C. Ninety patients with chronic hepatitis C, 30 with chronic hepatitis B and 25 healthy controls were enrolled. Alpha-defensins were identified and quantified in PBMCs by mass spectrometry, enzyme-linked immunosorbent assay, antibacterial activity and mRNA levels. PBMCs from three patients and controls were stimulated with HCV core protein, hepatitis B virus core antigen and the alpha-defensin mRNAs level was quantified. We found that HCV core protein activates in vitro the alpha-defensin transcription. Alpha-defensin levels in patients with chronic hepatitis C (mean +/- SD = 1.103 +/- 0.765 ng/10(6) cells), chronic hepatitis B (0.53 +/- 0.15) and healthy controls (0.217 +/- 0.09) resulted significantly different (P < 0.001). In patients with chronic hepatitis C, the alpha-defensin levels and antibacterial activity correlate with the liver fibrosis. Our data suggest that HCV induces alpha-defensin expression. The high linear correlation of alpha-defensin levels with advancing fibrosis makes the measure of these peptides a reliable marker to evaluate fibrosis stage.

Effects of temporins on molecular dynamics and membrane permeabilization in lipid vesicles

Temporins are a novel family of small (10-13 residues) cationic antimicrobial peptides recently isolated from the skin of the European red frog Rana temporaria. Although recently acquired evidence shows that temporins have the potential to kill bacteria by permeabilizing the cytoplasmic membrane, the molecular mechanisms of membrane selectivity and permeabilization are largely unknown. In this study, it was found that temporins cause the release of fluorescent markers entrapped in phosphatidylcholine liposomes in a manner that depends significantly on the size of the solute. Temporins were also shown to lack a detergent-like effect on lipid vesicles, indicating that marker leakage caused by these peptides is not due to total membrane disruption but to perturbation of bilayer organization on a local scale. Binding of temporins to liposomes did lead to a small increase in lipid hydrocarbon chain mobility, as revealed by EPR spectroscopy of nitroxide-labeled fatty acids incorporated in the bilayer. Reference experiments were conducted using the bee venom peptide melittin, whose properties and behavior in natural and model membrane systems are well known. Our findings for temporins are discussed in relation to the models proposed to date to account for the action of antimicrobial peptides on membranes.

Involvement of Rel factors in the expression of antimicrobial peptide genes in amphibia

Genes coding for antimicrobial peptides in amphibia reveal a remarkably high number of structural motifs for response elements, previously identified in the genes of insect antimicrobial peptides and in those of the mammalian acute phase response. This study focuses on the functional analysis of the bombinin gene promoter in a Drosophila blood cell line, and the identification of kappaB-binding factors in skin secretions of the frog Bombina orientalis. Transfection experiments demonstrated that the bombinin gene promoter was activated in a lipopolysaccharide-dependent manner, and that insect Rel factors target specific sequences in the amphibian gene promoter. After bathing frogs in bacteria, their skin secretions contained kappaB-specific binding complexes, indicating that Rel factors are crucial components in the response against gram-negative bacteria in this species. These results suggest that a common ancestral control mechanism governs the expression of the first line host-defence from insects to vertebrates.

Structure-function relationships in bombinins H, antimicrobial peptides from Bombina skin secretions

Skin secretions of amphibia of the Bombina genus contain two families of antimicrobial peptides, the bombinins (bombinin-like peptides) and the bombinins H (H for hydrophobic and hemolytic). The latter family includes a number of peptides containing a D-amino acid in the second position, in addition to their corresponding all L-isomers. The antimicrobial activity of three pairs of bombinin H isomers, H2/H4, H6/H7 and GH-1D/GH-1L, has been investigated. The first two pairs of peptides were actually isolated from the secretion, whereas the third was synthesized according to the sequence deduced from a gene coding for a bombinin-like peptide in Bombina orientalis.

Sequence of a gene from Bombina orientalis coding for the antimicrobial peptide BLP-7

The structure of a gene coding for bombinin-like peptides (BLP) in Bombina orientalis was determined. It comprises two exons separated by a 1337 bp intron. Exon 1 codes for the signal peptide, while exon 2 contains the genetic information for BLP-7 and a bombinin H-type peptide (GH-2). The promoter region contains putative recognition sites for nuclear factors, such as NF-IL6 and NF-kappaB. The analysis of the structure of this gene, compared with that of the previously reported BLP-3 gene sequence, suggests the occurrence of a gene duplication event, rather than an alternative splicing mechanism, which leads to the generation of both inter- and intra-families variability in this class of cytolytic peptides. Furthermore, chromosome walking analysis indicates that this gene family is not densely clustered.

Glutathione S-transferase, similar to sigma class, from skin secretions of Xenopus laevis

Using glutathione affinity chromatography followed by isoelectrofocusing, we purified from the skin secretion of Xenopus laevis an isoenzyme of glutathione S-transferase with an apparent subunit molecular mass of 22.5 kDa and an isoelectric point at pH 5.1. Its N-terminal amino acid sequence was highly similar to that of the sigma class glutathione S-transferase, which previously was demonstrated to have a glutathione-dependent prostaglandin D2 synthase activity. Immunohistochemistry analysis revealed that the isoenzyme was located in the cytoplasm of granular gland cells.

Antimicrobial peptides from amphibian skin: what do they tell us?

Amphibian skin secretions contain many biologically active compounds, such as biogenic amines, complex alkaloids, or peptides. Within the latter class of molecules, a large number of peptide antibiotics has been isolated and characterized from different amphibian species. Antimicrobial peptides are considered the effector molecules of innate immunity, acting as a first line of defense against bacterial infections, by perturbing the phospholipid bilayer of the target cell membrane. These gene-encoded molecules are synthesized as inactive precursors and in several cases their proparts were shown to have highly conserved structures. It has also been demonstrated that the promoter regions of inducible peptide antibiotics are often regulated by the transcriptional control machinery NF-kappa B/I kappa B alpha. In amphibia of Rana and Bombina genera, inhibition of transcription of the genes encoding antimicrobial peptides has been obtained by glucocorticoid treatment, which causes an increase of I kappa B alpha synthesis. Moreover, determination of the structure of a number of genes coding for antimicrobial peptides in amphibia has actually shown that their promoter regions contain recognition sites for nuclear factors.

Structure-function relationships of temporins, small antimicrobial peptides from amphibian skin

Temporins, antimicrobial peptides of 10-13 residues, were isolated from secretions of Rana temporaria [Simmaco, M., Mignogna, G., Canofeni, S., Miele, R., Mangoni, M.L. & Barra, D. (1996) Eur. J. Biochem. 242, 788-792]. These molecules are specific to this amphibian species, which is also able to secrete on its skin other antimicrobial peptides similar to those found in different Rana species. The effect of temporins A, B and D (13 residues, net charge +2), and H (10 residues, net charge +1 and +2, respectively) against both artificial membranes of differing lipid composition and bacteria has been investigated in order to gain insight into their mechanisms of action. The results indicate that: the lytic activity of temporins is not greatly affected by the membrane composition; temporins A and B allow the leakage of large-size molecules from the bacterial cells; temporin H renders both the outer and inner membrane of bacteria permeable to hydrophobic substances of low molecular mass; and temporin D, although devoid of antibacterial activity, has a cytotoxic effect on erythrocytes. The results allow important conclusions to be drawn about the minimal structural requirements for lytic efficiency and specificity of temporins.

Expression and activity of cyclic and linear analogues of esculentin-1, an anti-microbial peptide from amphibian skin

Esculentin-1 is a potent anti-microbial peptide present in minute amounts in skin secretions of Rana esculenta. It contains 46 amino-acid residues and a C-terminal disulfide bridge. We have explored the possibility of producing analogues of this peptide by recombinant expression in Escherichia coli of a fusion protein which is sequestered in inclusion bodies. The peptide of interest has been inserted at the N-terminus of the protein, from which it can be released by cyanogen bromide cleavage. The anti-microbial activities of the recombinant peptide as well as that of a mutant linear form devoid of the disulfide bridge are presented. The recombinant analogues retain the biological activity of the natural peptide, as tested with an inhibition zone assay against a variety of microorganisms. However, experiments on the rate of bacterial killing show that gram-negative bacteria are more sensitive to the peptides than the gram-positive bacterium, the effect of the cyclic peptide being in all cases faster than that of the linear molecule. Moreover, the activity against gram-negative bacteria for both peptides is not affected by salts, whereas the activity against Staphylococcus aureus is lost at high salt concentration.

Structure of pyridoxal kinase from sheep brain and role of the tryptophanyl residues

The primary structure of sheep brain pyridoxal kinase has been determined by direct chemical and physical methods. The enzyme contains 312 amino acid residues with an acetylated methionine at the N-terminus, yielding a molecular mass of 34,861 Da. The functional role played by the two tryptophanyl residues in positions 52 and 244 of the polypeptide chain has been investigated by fluorescence spectroscopy. The tryptophanyl residues are not completely exposed to the rapidly relaxing solvent and they are poorly accessible to collisional quenchers. Chemical modification with NBS abolishes the catalytic activity of the kinase. The amino acid sequence of the sheep brain enzyme shows high similarity (86.2% identity) with the human pyridoxal kinase recently reported [Hanna, Turner, and Kirkness, (1997), J. Biol. Chem. 272, 10756-10760]. Comparison of the mammalian proteins with bacterial and yeast putative pyridoxal kinases retrieved from the Swiss-Prot data bank shows a low degree of overall similarity. In particular, the putative ATP-binding domain is conserved, whereas the region that appears to be crucial in the binding of the pyridoxal substrate is not. Thus, the assignment of the bacterial and yeast cDNA-deduced proteins as pyridoxal kinases should be taken with caution.

Occurrence and function of D-amino acid-containing peptides and proteins: antimicrobial peptides

Antimicrobial peptides are widely distributed in living organisms, where they represent a constitutive defence system acting as a first line of response against infections. The number of such peptides discovered has increased rapidly in the last few years, and more than 100 have been described from different sources. So far, antimicrobial peptides containing a D-amino acid have only been found in the skin secretions of frogs belonging to the genus Bombina. In the second position of the sequence of the mature peptides either D-alloisoleucine or D-leucine were detected. The D-amino acids are derived from the corresponding L forms by an as yet unknown posttranslational reaction.

Characterization and analysis of D-amino acids

The need to screen a large number of natural extracts, with the aim of detecting D-amino acids or isolating and characterizing peptides containing them, has stimulated the development of novel and improved procedures for the analysis of amino acid enantiomeric mixtures, with special attention paid to automation. Different methods for the analysis of D-amino acids are described and discussed.

Experimental infections of Rana esculenta with Aeromonas hydrophila: a molecular mechanism for the control of the normal flora

Frogs can be useful models for studying the mechanisms that may regulate their natural microbial flora. Their skin glands produce a secretion containing 20-30 different peptides, some antimicrobial some neurotrophic. As they often live in soil or silt that is rich in microbes, they can be expected to be able to prevent or eliminate infections in very short periods of time. The bacterium Aeromonas hydrophila is widely distributed in nature and is considered as part of the natural flora of frogs and many animals, including humans. From an alternative frog strain of A. hydrophila, Bo-3, we isolated a spontaneous and stable mutant (Bo-3N), resistant to nalidixic acid, here used to follow the host-microbe interactions in experimental infection of mouth and skin of Rana esculenta. The skin peptides had been previously isolated, sequenced and cloned. We showed that skin treatment with a glucocorticoid (GC) cream blocked de novo synthesis of these peptides and, simultaneously, prepropeptide mRNAs disappeared while IkappaBalpha was up-regulated. Experimental mouth infections with 20 million cells of A. hydrophila Bo-3N showed that a normal wild frog can eliminate the bacteria from the mouth within 15 min, while a frog pretreated with GC cream for 1 h could not reduce Bo-3N below 3500 colony-forming units (CFU)/5 microl 'saliva'. An in vitro comparison showed that frog blood or serum allowed bacteria to grow, while the skin secretion killed the bacteria within 10 min. Using different enzyme-linked immunosorbent assays (ELISAs) with rabbit anti-Bo-3 serum as a positive control, we were able to rule out immunoglobulin G (IgG) binding to A. hydrophila. An assay for immunoglobulin M (IgM) (or some other serum component) in frog serum showed binding to A. hydrophila only corresponding to a few per cent of the positive control. For skin infections we bathed the frogs for 10 min in an overnight culture of Bo-3N diluted to about 10(7) CFU/ml. Electrical stimulation after the bath showed, for the total secretion, a two to fourfold increase in the antibacterial activity, while a pretreatment with GC cream reduced the activity to about one-third of that of the non-bathed control frog. HPLC analysis of the peptide pattern confirmed these findings. The survival value of antimicrobial peptides have earlier been demonstrated in vivo and in vitro only in Drosophila. The present experiments are the first combined in vivo and in vitro demonstrations of the function of peptide antibiotics in a vertebrate. One such function is involved in the control of the natural flora.

Molecular cloning of a bombinin gene from Bombina orientalis: detection of NF-kappaB and NF-IL6 binding sites in its promoter

The sequence of a gene from Bombina orientalis was determined which codes for antibacterial peptides. The gene comprises two exons separated by a large intron. Exon 1 codes for the signal peptide, while exon 2 contains the genetic information for two identical bombinins and one bombinin H. The promoter region of the bombinin gene contains putative recognition sites for nuclear factors, such as NFkappaB and NF-IL6. In vivo experiments on B. orientalis have shown that a short contact with bacteria is sufficient to induce a marked increase in the amount of antibacterial peptides in the skin secretion of frogs. This increase was suppressed by pretreatment with glucocorticoids. In the latter case, a significant increase of I kappaB alpha in the secretion is also detectable.

Gene-encoded peptide antibiotics and innate immunity. Do 'animalcules' have defence budgets?

Gene-encoded peptide antibiotics have been isolated from plants, animals and microbes. Their protective role has been related to innate immunity, which has gradually become accepted across the biomedical community. The evidence for the immune function of peptide antibiotics has been convincingly demonstrated by a combination of both in vitro and in vivo data for plants and insects, but for vertebrates in vivo data are scarce. Using frogs as model systems, it has been shown that the genes for antibacterial peptides are down-regulated by glucocorticoids, while IkappaB alpha is clearly up-regulated. Experimental infections with frog bacteria have shown that the normal capacity to control the natural flora is lost after treatment with glucocorticoids. A low-specificity immune mechanism is cost-effective, something that may have been of importance during animal evolution.

Effect of glucocorticoids on the synthesis of antimicrobial peptides in amphibian skin

Gene-encoded peptide antibiotics are widespread in insects, plants and vertebrates and confer protection against bacterial and fungal infections. NF-kappaB is an important transcription factor for many immunity-related mammalian proteins and also for insect immune genes. The activity of NF-kappaB is regulated by the interaction with an inhibitor, I kappaB. It was recently demonstrated that glucocorticoids induce the synthesis of I kappaB in human cell lines. So far, all genes for peptide antibiotics have promoter motifs with NF-kappaB binding sites, but its actual function in peptide regulation has been studied only in insects. Here we show that glucocorticoid treatment of the frog Rana esculenta inhibits the transcription of all genes encoding antibacterial peptides by inducing the synthesis of I kappaB alpha. These results suggest that also in vertebrates peptide-mediated innate immunity is controlled by NF-kappaB-regulated transcription.

Temporins, antimicrobial peptides from the European red frog Rana temporaria

A cDNA library from the skin of Rana temporaria has been screened using a cDNA fragment probe that encodes the signal peptide of the precursor of esculentin from the skin secretion of Rana esculenta. With this approach, the cDNAs encoding the precursors of three peptides were isolated. Subsequently, the peptides predicted from the sequence of the cloned cDNAs as well as several structurally related peptides could be isolated from the skin secretion of R. temporaria. These peptides, which were named temporins, have a length of 10-13 residues and show some sequence similarity to hemolytic peptides isolated from Vespa venom [Argiolas, A. & Pisano, J. J. (1984) J. Biol. Chem. 259, 10106-10111]. Natural and synthetic temporins have antibacterial activity against gram-positive bacteria, but they are not hemolytic. Temporins are the smallest antibacterial peptides hitherto found in nature.

Amphibian skin: a promising resource for antimicrobial peptides

Amphibian skin is a rich source of biologically active compounds that are assumed to have diverse physiological and defence functions. In addition to the range of pharmacologically active peptides present, some of which have mammalian homologues, skin secretions contain a broad spectrum of antimicrobial peptides. As yet, such peptides from only a few species have been studied, and screening of other species is expected to yield further new antimicrobial activities. Natural antimicrobial peptides isolated from amphibian skin could provide lead structures for either the chemical, or rDNA synthesis of novel antimicrobials.

Primary structure and tissue distribution of human 4-aminobutyrate aminotransferase

cDNA encoding human 4-aminobutyrate aminotransferase (aminobutyrate:2-oxoglutarate aminotransferase) was prepared by polymerase chain reaction using mRNA from human neuroblastoma cells as the template and oligonucleotides synthesized on the basis of the information obtained from direct protein sequencing. The cDNA-deduced sequence enabled peptides, sequenced by automated Edman degradation, to be aligned for confirmation of the complete primary structure. The results are compared with the recently published sequence of the rat enzyme deduced entirely from DNA sequencing [Medina-Kauwe, L. K., Tillakaratne, N. J. K., Wu, J.-Y. & Tobin, A. J. (1994) J. Neurochem. 62, 1267-1275]. Although the sequences are almost identical for most of their length, they differ in a segment of 36 residues. Almost complete identity of the two sequences is established if it is assumed that a frame-shift error was introduced into the reported rat cDNA sequence. The human cDNA was used to probe for the presence of 4-aminobutyrate aminotransferase mRNA in human tissues and a significant transcript was found in heart, placenta and in tissues usually associated with the expression of this enzyme.

Antimicrobial peptides from skin secretions of Rana esculenta. Molecular cloning of cDNAs encoding esculentin and brevinins and isolation of new active peptides

Three cytolytic peptides, termed brevinin-1E, brevinin-2E, and esculentin, were isolated from skin secretions of the European frog Rana esculenta (Simmaco, M., Mignogna, G., Barra, D., and Bossa, F. (1993) FEBS Lett. 324, 159-161). Nucleotide sequence analysis of cDNAs coding for the corresponding precursors revealed that in all of them a single copy of the sequence of the mature peptide is present preceded by a dibasic cleavage site and followed by a stop codon. The signal peptides of these precursors show a clear homology to the corresponding region of the precursor of dermorphin, a neuropeptide occurring in the skin of amphibians of the subfamily Phyllomedusinae. Ten new peptides, ranging in size from 24 to 46 residues, all possessing an intramolecular disulfide bridge located at the carboxyl-terminal end, were isolated from skin secretions of R. esculenta. These peptides can be grouped into four subfamilies on the basis of their distinctive structural and/or functional properties. All of these new peptides have antimicrobial and/or hemolytic activities typical for the respective subfamily. In addition, we demonstrate that esculentin-1 also inhibits the growth of Pseudomonas aeruginosa, Candida albicans, and Saccharomyces cerevisiae.

[D-Leu2]deltorphin, a 17 amino acid opioid peptide from the skin of the Brazilian hylid frog, Phyllomedusa burmeisteri

A novel 17 amino acid peptide, having a D-leucine in position 2 of its sequence, has been isolated from methanol extracts of the skin of the Brazilian frog, Phyllomedusa burmeisteri. The sequence of the peptide is: Tyr-D-Leu-Phe-Ala-Asp-Val-Ser-Thr-Ile-Gly-Asp-Phe-Phe-His-Ser-Ile-NH2. It displays a poor affinity for delta-opioid binding sites, both in the periphery and in the central nervous system. However, the shorter synthetic amidated analogue (1-10) possess both on the central and peripheral delta binding sites an agonistic potency equalling in affinity and exceeding in selectivity that of the enkephalins. The shorter amidated analogue (1-7) is virtually inactive on opioid binding sites in the periphery, but displays a clear-cut affinity for both delta and mu binding sites on rat brain membranes. To date six different D-amino acid residues have been found, always in position 2 of the sequence, in as many as 11 natural peptide molecules of animal origin.

Antibacterial and haemolytic peptides containing D-alloisoleucine from the skin of Bombina variegata

A family of bombinin-related peptides is present in the skin of Bombina variegata. These peptides contain 27 residues with Gly as N-terminus and display antimicrobial activity. From sequence analysis of the cDNAs encoding for the corresponding peptide precursors, the presence of a novel 20-residue peptide with Ile as N-terminus was predicted. We have now purified a family of hydrophobic peptides named H1-H5, whose sequences correspond to the predicted peptide with some variability in positions 1, 2 and 8. In particular, H3-H5 contain a D-alloisoleucine residue in the second position. All these peptides display antibacterial and haemolytic activity.

Isolation and cloning of the gene from Escherichia coli encoding glutamate decarboxylase

We have isolated and cloned a 4.5-kb fragment containing the structural gene of glutamate decarboxylase from an overproducing strain of Escherichia coli. Sequencing of this fragment is in progress. The time course of glutamate decarboxylase expression has been also investigated.

Novel antimicrobial peptides from skin secretion of the European frog Rana esculenta

Three antimicrobial peptides were isolated from skin secretion of the European frog, Rana esculenta. Two of them show similarity to brevinin-1 and brevinin-2, respectively, two antimicrobial peptides recently isolated from a Japanese frog [Morikawa, N., Hagiwara, K. and Nakajima, T. (1992) Biochem. Biophys. Res. Commun. 189, 184-190]. The third one, named esculentin, is 46 residues long and represents a different type of peptide. All these peptides have as a common motif an intramolecular disulfide bridge located at the COOH-terminal end. The peptides from R. esculenta show distinctive antibacterial activity against representative Gram-negative and Gram-positive bacterial species. In particular, esculentin is the most active against Staphylococcus aureus, and has a much lower hemolytic activity.

Identification and characterization of two dermorphins from skin extracts of the Amazonian frog Phyllomedusa bicolor

Skin extracts of South American hylid frogs of the subfamily Phyllomedusinae contain dermorphins and deltorphins, opioid heptapeptides highly selective for either mu or delta receptors. In all these peptides, a D-amino acid is present in the second position. The structure of the precursors for Ala-deltorphins was recently deduced from cloned cDNAs derived from skin of Phyllomedusa bicolor (Richter et al. (1990) Proc. Natl. Acad. Sci. USA 87, 4836-4839). From the amino acid sequence of these precursors, the existence of three peptides related to dermorphin could be predicted. From methanol extracts of skin of Ph. bicolor we have isolated two of these peptides, [Lys7]dermorphin-OH and [Trp4,Asn7]dermorphin-OH. The biological activity of these new dermorphins and their amidated counterparts is presented.

Determination of the chirality of amino acid residues in the course of subtractive Edman degradation of peptides

A chiral reagent, 1-fluoro-2,4-dinitro-5-L-alanine, was synthesized for the analysis of enantiomeric mixtures of amino acids after precolumn derivatization. The resulting diastereomers can be separated and quantitated by microbore RP-HPLC. These derivatives are relatively stable under the conditions used for acid hydrolysis of peptide bonds. Thus, this reagent was included in the protocol of a subtractive Edman degradation procedure of peptides to determine the sequence position of amino acid residues with concomitant identification of their chirality at a nanomolar level.

A family of bombinin-related peptides from the skin of Bombina variegata

A peptide fraction was isolated from the skin of Bombina variegata that showed antimicrobial activity. This fraction contained several molecular species, all of them consisting of 27 amino acid residues, with a constant C-terminal region (from residues 14-27), including an amidated carboxyl end and a variable N-terminal segment. These peptides are related but not identical to bombinin [Csordas, A. & Michl, H. (1970) Monatsh. Chem. 101, 182-189]. By using synthetic oligonucleotides corresponding to the C-terminal region of the peptides, a cDNA library from the skin of B. variegata was screened and several positive clones coding for the corresponding peptide precursors were isolated and sequenced. Each clone contained the genetic information for a different bombinin-like peptide. The antimicrobial activity towards different bacterial species of a synthetic peptide corresponding to one of the variants deduced from cDNA sequences was tested. This peptide was found to be mainly active against different isolates of Staphylococci and Escherichia coli.

Mechanism of inactivation and identification of sites of modification of ornithine aminotransferase by 4-aminohex-5-ynoate

The inactivation of ornithine aminotransferase by an enzyme-activated irreversible inhibitor 4-aminohex-5-ynoate was accompanied by stoichiometric binding of the radiolabeled compound. Distribution of radiolabel among separated tryptic peptides indicated that more than one amino acid residue had reacted. Lys-292 and Cys-388 were positively identified. Reduction with borohydride was necessary to stabilize the adduct formed with Lys-292, and the relevant peptide prepared after this treatment contained equimolar amounts of inhibitor and coenzyme. The coenzyme chromophore in this peptide showed strong negative circular dichroism. A mechanism consistent with these observations is proposed.

Structure of syringotoxin, a bioactive metabolite of Pseudomonas syringae pv. syringae

The covalent structure of syringotoxin, a bioactive metabolite of Pseudomonas syringae pv. syringae isolates, pathogenic on various species of citrus trees, has been deduced from 1D and 2D 1H- and 13C-NMR spectra combined with extensive FAB-MS data and results of some chemical reactions. Similarly to syringomicins and syringostatins, produced by other plant pathogenic strains of P. syringae pv. syringae, syringotoxin is a lipodepsinonapeptide. Its peptide moiety corresponds to Ser-Dab-Gly-Hse-Orn-aThr-Dhb-(3-OH)Asp-(4-Cl)Thr with the terminal carboxy group closing a macrocyclic ring on the OH group of the N-terminal Ser, which in turn is N-acetylated by 3-hydroxytetradecanoic acid.