Isolation and cDNA cloning of an antibacterial L-amino acid oxidase from the skin mucus of the great sculpin Myoxocephalus polyacanthocephalus

Comprehensive analysis of the lncRNAs, mRNAs, and miRNAs implicated in the immune response of Pinctada fucata martensii to Vibrio parahaemolyticus

Non-coding RNAs (ncRNAs) have been implicated in a variety of biological processes. However, most ncRNAs are of unknown function and are as-yet unannotated. The immune-related functions of ncRNAs in the pearl oyster Pinctada fucata martensii were explored based on transcriptomic differences in the expression levels of long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and messenger RNAs (mRNAs) in the hemocytes of P.f. martensii after challenge by the pathogenic bacterium Vibrio parahaemolyticus. Across the challenged and control pearl oysters, 144 miRNAs and 14,571 lncRNAs were identified. In total, 13,375 ncRNAs were differentially expressed between the challenged and control pearl oysters; in the challenged pearl oysters as compared to the controls, 15 miRNAs and 5147 lncRNAs were upregulated, while 51 miRNAs and 8162 lncRNAs were downregulated. The sequencing results were validated using quantitative real-time polymerase chain reaction (qRT-PCR) analysis. GO and KEGG pathway analysis showed that genes targeted by the differentially expressed ncRNAs were associated with the vascular endothelial growth factor (VEGF) signaling pathway and the nuclear factor kappa-B (NF-κB) signaling pathway. An lncRNA-mRNA-miRNA network that was developed based on the transcriptomic results of this study suggested that lncRNAs may compete with miRNAs for mRNA binding sites. This study may provide a useful framework for the detection of additional novel ncRNAs, as well as new insights into the pathogenic mechanisms underlying the response of P.f. martensii to V. parahaemolyticus.

Seawater activates l-amino acid oxidase from the serum of the red-spotted grouper Epinephelusakaara

l-amino acid oxidases (LAOs) catalyze the oxidative deamination of l-amino acid and generate α-keto acid, ammonia, and hydrogen peroxide as byproducts. LAOs showed the variety of bioactivity by the resulting hydrogen peroxide. The serum of the red-spotted grouper Epinephelus akaara contains an LAO (Ea-LAO) with the potential to kill bacterial pathogens Aeromonas salmonicida and Vibrio anguillarum via hydrogen peroxide. However, it is unknown how the grouper tolerates the harmful effects of the serum Ea-LAO byproducts. In this study, we analyzed the kinetics of fish LAOs to understand how they escape the toxicity of byproducts. The LAO activity of grouper serum was suppressed in low-salt solutions such as NaCl, CaCl₂, MgCl₂, and diluted seawater. The activity was non-linearly increased and fitted to the four-parameter log-logistic model. The EC₅₀ of the seawater was calculated to have a 0.72-fold concentration. This result suggested that the Ea-LAO could be activated by mixing with seawater. The results of circular dichroism spectroscopy showed that the α helix content was estimated to be 12.1% and 5.3% in a salt-free buffer (inactive condition) and the original concentration of seawater (active condition), respectively, indicating that the secondary structure of the Ea-LAO in the active condition was randomized. In addition, the Ea-LAO showed reversible LAO activity regulation according to the salt concentration in the environment. Taken together, this indicates that the Ea-LAO is normally on standby as an inactive form, and it could activate as a host-defense molecule to avoid pathogen invasion via a wound when mixed with seawater.

Identification and characterization of l-amino acid oxidase 2 gene in orange-spotted grouper (Epinephelus coioides)

Recently, l-amino acid oxidases (LAAOs) have been identified in several fish species as first-line defense molecules against bacterial infection. Here, we report the cloning and characterization of a fish LAAO gene, EcLAAO2, from orange-spotted grouper (Epinephelus coioides). The full-length cDNA is 3030 bp, with an ORF encoding a protein of 511 amino acids. EcLAAO2 is mainly expressed in the fin, gill, and intestine. Its expression is upregulated in several immune organs after challenge with lipopolysaccharide (LPS) and poly (I:C). The recombinant EcLAAO2 protein (rEcLAAO2), expressed and purified from a baculovirus expression system, was determined to be a glycosylated dimer. According to a hydrogen peroxide-production assay, the recombinant protein was identified as having LAAO enzyme activity with substrate preference for L-Phe and L-Trp, but not L-Lys as other known fish LAAOs. rEcLAAO2 could effectively inhibit the growth of Vibrio parahaemolyticus, Staphylococcus aureus, and Bacillus subtilis while exhibiting less effective inhibition of the growth of Escherichia coli. Finally, protein models based on sequence homology were constructed to predict the three-dimensional structure of EcLAAO2 as well as to explain the difference in substrate specificity between EcLAAO2 and other reported fish LAAOs. In conclusion, this study identifies EcLAAO2 as a novel fish LAAO with a substrate preference distinct from other known fish LAAOs and reveals that it may function against invading pathogens.

Antimicrobial properties of L-amino acid oxidase: biochemical features and biomedical applications

Abstract

Mucus layer that covers the body surface of various animal functions as a defense barrier against microbes, environmental xenobiotics, and predators. Previous studies have reported that L-amino acid oxidase (LAAO), present in several animal fluids, has potent properties against pathogenic bacteria, viruses, and parasites. LAAO catalyzes the oxidative deamination of specific L-amino acids with the generation of hydrogen peroxide and L-amino acid metabolites. Further, the generated hydrogen peroxide is involved in oxidation (direct effect) while the metabolites activate immune responses (indirect effect). Therefore, LAAO exhibits two different mechanisms of bioactivation. Previously, we described the selective, specific, and local oxidative and potent antibacterial actions of various LAAOs as potential therapeutic strategies. In this review, we focus on their biochemical features, enzymatic regulations, and biomedical applications with a view of describing their probable role as biochemical agents and biomarkers for microbial infections, cancer, and autoimmune-mediated diseases. We consider that LAAOs hold implications in biomedicine owing to their antimicrobial activity wherein they can be used in treatment of infectious diseases and as diagnostic biomarkers in the above-mentioned diseased conditions.

Key points

•Focus on biochemical features, enzymatic regulation, and biomedical applications of LAAOs.

•Mechanisms of antimicrobial activity, inflammatory regulation, and immune responses of LAAOs.

•Potential biomedical application as an antimicrobial and anti-infection agent, and disease biomarker.

Expression profile of the fish immune enzyme l-amino acid oxidase (LAAO) after Streptococcus agalactiae infection in zebrafish (Danio rerio)

l-amino acid oxidase (LAAO) is a recently discovered novel fish immune enzyme. To explore the role of LAAO in the immune system of bony fishes, we cloned the full-length coding sequence (CDS) of LAAO of the zebrafish Danio rerio (ZF-LAAO), conducted bioinformatics analysis of ZF-LAAO, and analyzed its expression profile in zebrafish infected with the pathogen Streptococcus agalactiae. The CDS of ZF-LAAO was 1,515 base pairs long, and the encoded protein of ZF-LAAO contained an 18 amino acid signal peptide. ZF-LAAO contained the conserved domains of the LAAO family (dinucleotide binding motif and GG-motif), 2 N-glycosylation sites, and 2 O-glycosylation sites, and it was a stable hydrophilic exocrine protein. Similarity of the amino acid sequence of ZF-LAAO with LAAOs of 14 other bony fish species was >50% in all cases. The greatest similarity (79.45%) was with the LAAO of Anabarilius grahami, and these two LAAOs were grouped together in the phylogenetic tree. In wild-type zebrafish infected with S. agalactiae, changes in ZF-LAAO gene (zflaao) expression occurred mainly in the early stage of infection, and the changes in zflaao expression were more pronounced than those of the immune enzyme lysozyme (LYZ). The expression levels of both LYZ gene of zebrafish (zflyz) and zflaao were significantly elevated at 6 h after infection (p < 0.001), but zflyz expression in the spleen decreased at 12 h whereas zflaao expression in the liver and spleen peaked at 12 h. These results provided a reference for functional studies of the novel immune enzyme LAAO in bony fish.

Plasma pharmacokinetics and tissue distribution of L-lysine α-oxidase from Trichoderma cf. aureoviride RIFAI VKM F- 4268D in mice

L-lysine α-oxidase (LO) is an L-amino acid oxidase with antitumor, antimicrobial and antiviral properties. Pharmacokinetic (PK) studies were carried out by measuring LO concentration in plasma and tissue samples by enzyme immunoassay. L-lysine concentration in samples was measured spectrophotometrically using LO. After single i.v. injection of 1.0, 1.5, 3.0 mg/kg the circulating T_1/2 of enzyme in mice varied from 51 to 74 min and the AUC_0-inf values were 6.54 ± 0.46, 8.66 ± 0.59, 9.47 ± 1.45 μg/ml × h, respectively. LO was distributed in tissues and determined within 48 h after administration with maximal accumulation in liver and heart tissues. Mean time to reach the maximum concentration was highest for the liver-9 h, kidney-1 h and 15 min for the tissues of heart, spleen and brain. T_1/2 of LO in tissues ranged from 7.75 ± 0.73 to 26.10 ± 2.60 h. In mice, plasma L-lysine decreased by 79% 15 min after LO administration in dose 1.6 mg/kg. The serum L-lysine levels remained very low from 1 to 9 h (< 25 μM, 17%), indicating an acute lack of L-lysine in animals for at least 9 h. Concentration of L-lysine in serum restored only 24 h after LO administration. The results of LO PK study show that it might be considered as a promising enzyme for further investigation as a potential anticancer agent.

Blood loss induces l-amino acid oxidase gene expression in the head kidney of the red-spotted grouper, Epinephelus akaara

In fish, the innate immune system is more important than the adaptive immune system because it responds quickly and nonspecifically to protect against pathogens. Thus, a variety of innate immune molecules have been found in fish. Recently, l-amino acid oxidases (LAOs) were discovered as a new member of the antibacterial protein from fish skin mucus and serum. In this study, we newly found an antibacterial LAO in red-spotted grouper (Epinephelus akaara) serum. It showed a broad range of substrate specificity with aromatic and hydrophobic amino acids. The grouper LAO gene had a low expression level in the kidney under normal conditions; however, it was significantly upregulated by blood loss 1 day after bleeding. In addition, the LAO activity in the serum recovered within 3 days in the same experiment. This quick recovery may indicate that the LAO is an essential innate immune molecule in the whole grouper body.

l-Amino acid oxidase as a fish host-defense molecule

An l-amino acid oxidase (LAO) is an amino acid metabolism enzyme that also performs a variety of biological activities. Recently, LAOs have been discovered to be deeply involved in innate immunity in fish because of their antibacterial and antiparasitic activity. The determinant of potent antibacterial/antiparasitic activity is the H₂O₂ byproduct of LAO enzymatic activity that utilizes the l-amino acid as a substrate. In addition, fish LAOs are upregulated by pathogenic bacteria or parasite infection. Furthermore, some fish LAOs show that the target specificity depends on the virulence of the bacteria. All results reflect that LAOs are new innate immune molecules. This review also describes the potential of the immunomodulatory functions of fish LAOs, not only the innate immune function by a direct oxidation attack of H₂O₂.

l-amino acid oxidase expression profile and biochemical responses of rabbitfish (Siganus oramin) after exposure to a high dose of Cryptocaryon irritans

Cryptocaryon irritans is an important protozoan parasite which infects almost all kinds of marine teleosts, causing heavy economic losses. In our previous studies, we found that rabbitfish (Siganus oramin) displayed high resistance to C. irritans infection, and a novel protein, l-amino acid oxidase (LAAO), was identified from the serum that was lethal to C. irritans. In this study, the rabbitfish were firstly infected with a high dose of C. irritans, then the LAAO mRNA expression pattern and the activity of three enzymes [superoxide dismutase (SOD), Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase] were measured in various tissues. The results indicated that, after infection, the feeding and swimming of rabbitfish was normal, and the infection intensity in the host was low. Tissue distribution analysis showed that LAAO mRNA was most pronounced in the head kidney and gill, with lower expression observed in the muscle. After infection with C. irritans, the LAAO mRNA was up-regulated early post infection (from 6 to 24 h) in both gill and spleen, but then returned to normal levels, implying that LAAO may play an important role in the host's early immune response. The SOD activity in the liver was significantly higher in the infection group than in the control group by 48 h post infection, while Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase activities in the gill were decreased by 12 and 24 h after infection; no significant difference was detected at the other time points throughout the experiment. Together, these results suggest that biochemical responses of rabbitfish are relatively mild after infection with a high dose of parasite, and the LAAO may play an important role in the host's defense against C. irritans.

Antimicrobials from Cnidarians. A New Perspective for Anti-Infective Therapy?

The ability of microbes to counter the scientific and therapeutic advancements achieved during the second half of the twentieth century to provide effective disease treatments is currently a significant challenge for researchers in biology and medicine. The discovery of antibiotics, and the subsequent development of synthetic antimicrobial compounds, altered our therapeutic approach towards infectious diseases, and improved the quality and length of life for humans and other organisms. The current alarming rise in cases of antibiotic-resistance has forced biomedical researchers to explore new ways to recognize and/or produce new antimicrobials or to find other approaches for existing therapeutics. Aquatic organisms are known to be a source of compounds having the potential to play a role in fighting the battle against pathogenic microbes. In this connection, cnidarians occupy a pre-eminent role. Over the past few decades several studies have explored the antimicrobial/antibiotic properties of cnidarian extracts with the aim of isolating compounds possessing useful therapeutic features. This paper aims to review the existing data on this subject, taking into account the possible utilization of identified compounds.

Distribution in Different Organisms of Amino Acid Oxidases with FAD or a Quinone As Cofactor and Their Role as Antimicrobial Proteins in Marine Bacteria

Amino acid oxidases (AAOs) catalyze the oxidative deamination of amino acids releasing ammonium and hydrogen peroxide. Several kinds of these enzymes have been reported. Depending on the amino acid isomer used as a substrate, it is possible to differentiate between l-amino acid oxidases and d-amino acid oxidases. Both use FAD as cofactor and oxidize the amino acid in the alpha position releasing the corresponding keto acid. Recently, a novel class of AAOs has been described that does not contain FAD as cofactor, but a quinone generated by post-translational modification of residues in the same protein. These proteins are named as LodA-like proteins, after the first member of this group described, LodA, a lysine epsilon oxidase synthesized by the marine bacterium Marinomonas mediterranea. In this review, a phylogenetic analysis of all the enzymes described with AAO activity has been performed. It is shown that it is possible to recognize different groups of these enzymes and those containing the quinone cofactor are clearly differentiated. In marine bacteria, particularly in the genus Pseudoalteromonas, most of the proteins described as antimicrobial because of their capacity to generate hydrogen peroxide belong to the group of LodA-like proteins.

Interaction of a snake venom L-amino acid oxidase with different cell types membrane

Snake venom l-amino acid oxidases are multifunctional enzymes that exhibited a wide range of pharmacological activities. Although it has been established that these activities are primarily caused by the H2O2 generated in the enzymatic reaction, the molecular mechanism, however, has not been fully investigated. In this work, LAAO interaction with cytoplasmic membranes using different cell types and Langmuir interfacial monolayers was evaluated. The Cerastes cerastes venom LAAO (CC-LAAO) did not exhibit cytotoxic activities against erythrocytes and peripheral blood mononuclear cells (PBMC). However, CC-LAAO caused cytotoxicity on several cancer cell lines and induced platelet aggregation in dose-dependent manner. Furthermore, the enzyme showed remarkable effect against Gram-positive and Gram-negative bacteria. These activities were inhibited on the addition of catalase or substrate analogs, suggesting that H2O2 liberation× is required for these effects. Binding studies revealed that CC-LAAO binds to the cell surface and enables the production of highly localized concentration of H2O2 in or near the binding interfaces. On another hand, the interaction of CC-LAAO with a mimetic phospholipid film was evaluated, for the first time, using a monomolecular film technique. Results indicated that phospholipid/CC-LAAO interactions are not involved in their binding to membrane and in their pharmacological activities.

Antibacterial properties of L-amino acid oxidase: mechanisms of action and perspectives for therapeutic applications

Venom, the mucus layer covering the body surface, ink glands, mammary glands, milk, and various animal secretory functions as both a physical and chemical defense barrier against bacteria and virus infections. Previously, several studies reported that L-amino acid oxidases (LAAOs) present in animal secretary fluids have strong antimicrobial activities and selective cytotoxic activities against Gram-positive and Gram-negative bacteria, various pathogenic bacteria, viruses, and parasite species. These LAAOs catalyze oxidative deamination of an L-amino acid substrate with the generation of hydrogen peroxide. The antibacterial activity of LAAOs is completely inhibited by catalase; thus, LAAOs kill bacteria by the hydrogen peroxide generated from the oxidation of L-amino acid substrates. This review focuses on the selective, specific, and local antibacterial actions of various LAAOs that may be used as novel therapeutic agents against infectious diseases. LAAOs that are suitable leads for combating multidrug-resistant bacterial infections are also studied.

Identification of the Atlantic cod L-amino acid oxidase and its alterations following bacterial exposure

Antibacterial factors that are present in epidermal mucus of fish have a potential role in the first line of host defence to bacterial pathogens. This study reports the identification of L-amino acid oxidase (LAO) in Atlantic cod (GmLao) and the changes in the molecule following bacterial exposure. The gmlao transcripts and LAO activity were present on both the body surface and in the internal organs of the fish. Relative mRNA level of gmlao increased significantly in the gills, the spleen and the head kidney (up to 8-fold) of fish that were challenged with the pathogen Vibrio anguillarum. The gmlao expression in skin was 4-fold higher in challenged fish. Our data indicate that LAO may be an important effector of antibacterial defence in Atlantic cod.

[Effect of L-lysine alpha-oxidase from Trichoderma cf. aureoviride Rifai ВКМF-4268D on pheochromocytoma PC12 cell line]

L-Amino acid oxidases (L-ААО, EC 1.4.3.2) comprise a group of flavoproteins, catalyzing oxidative deamination of L-alpha amino acids to the corresponding alpha-keto acids, NH3 and Н2О2. In most cases these enzymes present homodimeric molecules with a molecular mass of 100-150 kDa, which were shown to possess antiviral, antifungal and antitumor activity. L-lysine alpha-oxidase (LO) holds an outstanding place among this group of enzymes and its biological role may differ significantly from the other L-AAO, because it cleaves an essential amino acid - L-lysine without significant action on the other amino acids. Although much research has examined LO effects in the organism, the molecular basis of these effects is yet to be identified. To fill this gap, the present work addressed one of hypothetical mechanisms of LO biological action using the enzyme from Trichoderma cf. aureoviride Rifai ВКМF-4268D and rat pheochromocytoma PC-12 as a model cell line. Using flow cytometry a dose-dependent cytotoxicity of LO was shown. The significant growth of intracellular reactive oxygen species levels, detected by 2,7-dichlorodihydrofluorescein assay, implies generation of peroxide as one of the molecular mechanisms of LO cytotoxic action, although this does not rule out other probable ways of LO action in the organizm.

Recombinant production and evaluation of an antibacterial L-amino acid oxidase derived from flounder Platichthys stellatus

Fish produce mucus substances as a defensive outer barrier against several bacterial infections. We have recently identified an antibacterial L-amino acid oxidase (psLAAO1) in the mucus layer of the flounder Platichthys stellate. In this study, the antibacterial protein psLAAO1 was expressed as a secretory bioactive recombinant protein in the methylotrophic yeast Pichia pastoris. The recombinant psLAAO1 inhibited the growth of bacteria to the same levels as native psLAAO1 present in mucus. In particular, Staphylococci and Yersinia were strongly suppressed, showing the highest growth retardation of the 21 species and strains tested. Moreover, Staphylococcus epidermidis was most sensitive to psLAAO1 with a minimum inhibitory concentration (MIC) of 0.078 μg/mL, whereas Escherichia coli was essentially resistant to psLAAO1 with a MIC of >10 μg/mL. Interestingly, psLAAO1-treated E. coli were found to upregulate the expression of the btuE gene, which encodes glutathione peroxidase (GPx). The biochemical function of GPx is to reduce free hydrogen peroxide and is induced under response to reactive oxygen species (ROS). Thus, E. coli confers resistance to the reduced free hydrogen peroxide produced by psLAAO1 by increasing GPx levels. Furthermore, the growth of Staphylococcus aureus was completely inhibited in the presence of recombinant psLAAO1. The morphology of psLAAO1-treated S. aureus showed cell surface damage, the formation of large aggregates and the cells showed severe deformations. Western blot analysis showed that psLAAO1 binds to the surface of S. aureus. Therefore, psLAAO1 binds to the surface of LAAO-sensitive S. aureus and directs peroxidative activity at the surface of the bacterial membrane.

Functional expression of L-lysine α-oxidase from Scomber japonicus in Escherichia coli for one-pot synthesis of L-pipecolic acid from DL-lysine

L-Pipecolic acid is a key component of biologically active molecules and a pharmaceutically important chiral building block. It can be stereoselectively produced from L-lysine by a two-step bioconversion involving L-lysine α-oxidase and ∆(1)-piperideine-2-carboxylae (Pip2C) reductase. In this study, we focused on an L-lysine α-oxidase from Scomber japonicus that was originally identified as an apoptosis-inducing protein (AIP) and applied the enzyme to one-pot fermentation of L-pipecolic acid in Escherichia coli. A synthetic gene coding for an AIP was expressed in E. coli, and the recombinant enzyme was purified and characterized. The purified enzyme was determined to be a homodimer with a molecular mass of 133.9 kDa. The enzyme essentially exhibited the same substrate specificity as the native enzyme. Optimal temperature and pH for the enzymatic reaction were 70 °C and 7.4, respectively. The enzyme was stable below 60 °C and at a pH range of 5.5-7.5 but was markedly inhibited by Co(2+). To establish a one-pot fermentation system for the synthesis of optically pure L-pipecolic acid from DL-lysine, an E. coli strain carrying a plasmid encoding AIP, Pip2C reductase from Pseudomonas putida, lysine racemase from P. putida, and glucose dehydrogenase from Bacillus subtilis was constructed. The one-pot process produced 45.1 g/L of L-pipecolic acid (87.4 % yield from DL-lysine) after a 46-h reaction with high optical purity (>99.9 % enantiomeric excess).

Antibacterial efficacy of recombinant Siganus oramin L-amino acid oxidase expressed in Pichia pastoris

Siganus oraminl-amino acid oxidase is a novel natural protein (named SR-LAAO) isolated from serum of the rabbitfish (S. oramin), which showed antibacterial activity against both Gram-positive and Gram-negative bacteria and had a lethal effect on the parasites Cryptocaryon irritans, Trypanosoma brucei brucei and Ichthyophthirius multifiliis. In order to test whether recombinant SR-LAAO (rSR-LAAO) produced by the eukaryotic expression system also has antimicrobial activity, the yeast Pichia pastoris was used as the expression host to obtain rSR-LAAO in vitro. Crude rSR-LAAO produced by P. pastoris integrated with the SR-LAAO gene had antibacterial activity against both Gram-positive and Gram-negative bacteria as shown by inhibition zone assay of the antibacterial spectrum on agar plates. The average diameter of the inhibition zone of crude rSR-LAAO against the Gram-positive bacteria Staphylococcus aureus and Streptococcus agalactiae was 1.040 ± 0.045 cm and 1.209 ± 0.085 cm, respectively. For the Gram-negative bacteria Aeromonas sobria, Escherichia coli, Vibrio alginolyticus, Vibrio cholera and Photobacterium damselae subsp. piscicida, the average diameter of inhibition zone was 1.291 ± 0.089 cm, 0.943 ± 0.061 cm, 0.756 ± 0.057 cm, 0.834 ± 0.023 cm and 1.211 ± 0.026 cm, respectively. These results were obtained at the logarithmic growth phase of S. agalactiae and A. sobria cell suspensions after incubation with 0.5 mg/mL crude rSR-LAAO for 24 h. The final bacterial growth rate was decreased significantly. The relative inhibition rate can reach 50% compared to crude products from P. pastoris integrated with an empty vector at the same concentration of protein. The antimicrobial activity of crude rSR-LAAO was likely associated with H2O2 formation, because its inhibition zones were disturbed significantly by catalase. Scanning electron microscopy results showed crude rSR-LAAO-treated bacterial surfaces became rough and particles were attached, cell walls were retracted and cell membranes were ruptured. Together, the results of this study indicated rSR-LAAO from the P. pastoris expression system is a potential antibiotic for application as a therapeutic agent against bacterial diseases.

Crystallization and preliminary X-ray diffraction studies of an L-amino-acid oxidase from Lachesis muta venom

Snake-venom proteins form multi-component defence systems by the recruitment and rapid evolution of nonvenomous proteins and hence serve as model systems to understand the structural modifications that result in toxicity. L-Amino-acid oxidases (LAAOs) are encountered in a number of snake venoms and have been implicated in the inhibition of platelet aggregation, cytotoxicity, haemolysis, apoptosis and haemorrhage. An L-amino-acid oxidase from Lachesis muta venom has been purified and crystallized. The crystals belonged to space group P2₁, with unit-cell parameters a=66.05, b=79.41, c=100.52 Å, β=96.55°. The asymmetric unit contained two molecules and the structure has been determined and partially refined at 3.0 Å resolution.

Heterologous expression of l-lysine α-oxidase from Scomber japonicus in Pichia pastoris and functional characterization of the recombinant enzyme

Fish have a complex self-defense mechanism against microbial invasion. Recently, l-lysine α-oxidases have been identified from a number of fish species as a novel type of antibacterial protein in the integument. These enzymes exhibit strict substrate specificity for l-lysine, but the underlying mechanisms and details of their catalytic properties remain unknown. In this study, a synthetic gene coding for Scomber japonicus l-lysine α-oxidase, originally termed AIP (for apoptosis-inducing protein), was expressed in Pichia pastoris, and the recombinant enzyme (rAIP) was purified and characterized. rAIP exhibited essentially the same substrate specificity as the native enzyme, catalyzing the oxidative deamination of l-lysine as an exclusive substrate. rAIP was N-glycosylated and remained active over a wide range of pH, with an optimal pH of 7.5. The enzyme was stable in the pH range from 4.5 to 10.0 and was thermally stable up to 60°C. A molecular modelling of rAIP and a comparative structure/sequence analysis with homologous enzymes indicate that Asp(220) and Asp(320) are the substrate-binding residues that are likely to confer exclusive substrate specificity for l-lysine on the fish enzymes.

Siganus oramin recombinant L-amino acid oxidase is lethal to Cryptocaryon irritans

A novel antimicrobial and antiparasitic protein (APP/SR-LAAO) isolated from serum of the rabbitfish (Siganus oramin) was confirmed to be lethal to Cryptocaryon irritans, an important marine parasitic ciliate that causes marine white spot disease in a variety of wild and cultured fish. In this study, a recombinant SR-LAAO (rSR-LAAO) was expressed on a large scale in Escherichia coli Rosetta-gami™(DE3)pLysS cells. rSR-LAAO was expressed as an inactive form in the inclusion bodies. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that after purification, refolding and ultrafiltration, rSR-LAAO had a significantly cytotoxic effect on C. irritans theronts. Using light microscopy, scanning electron microscopy and fluorescence microscopy, we found that theronts rapidly became weakly motile, cilia became detached, cells became rounded, membranes eventually lysed in different cell positions and cytoplasmic contents leaked out of the cell. These results suggested the recombinant SR-LAAO was significantly lethal to C. irritans and the death process of the parasite incubated with rSR-LAAO was remarkably similar compared to the SR-LAAO group as reported earlier.

Intra-tissue localization of an antibacterial L-amino acid oxidase in the rockfish Sebastes schlegeli

The rockfish Sebastes schlegeli skin mucus contains a potent antibacterial protein, SSAP (S. schlegeli antibacterial protein), a novel l-amino acid oxidase with strict substrate specificity that acts against water-borne Gram-negative bacteria. We previously demonstrated that SSAP distributes in the skin and gills. Here we investigated the intra-tissue localization of SSAP in the tissues by in situ hybridization. Skin and gill sections were hybridized with digoxigenin-conjugated SSAP-specific RNA probe. SSAP mRNA-positive cells located near the basal membrane of skin epidermis and the gill epithelium. Furthermore, skin section was analyzed by immunohistochemistry and reacted with anti-SSAP antiserum as a primary antibody. The mucus layer and mucous cells in the skin were immunopositive. Skin and gill extracts produced hydrogen peroxide, responsible for antibacterial activity, in the presence of l-lysine. These results suggested that SSAP functions locally as a humoral defense factor in S. schlegeli skin and gills and prevents pathogenic bacterial invasion.

Advances in non-snake venom L-amino acid oxidase

L-amino acid oxidase is widely found in diverse organisms and has different properties. It is thought to contribute to antimicrobial activity, amino acid catabolism, and so forth. The purpose of this communication is to summarize the advances in non-snake venom L-amino acid oxidase, including its enzymatic and structural properties, gene cloning and expression, and biological function. In addition, the mechanism of its biological function as well as its application is also discussed.

Crystallization and preliminary X-ray diffraction analysis of an L-amino-acid oxidase from Bothrops jararacussu venom

Snake-venom L-amino-acid oxidases (SV-LAAOs) trigger a wide range of local and systematic effects, including inhibition of platelet aggregation, cytotoxicity, haemolysis, apoptosis and haemorrhage. These effects mainly arise from the uncontrolled release of the hydrogen peroxide that is produced by the redox reaction involving L-amino acids catalyzed by these flavoenzymes. Taking their clinical relevance into account, few SV-LAAOs have been structurally characterized and the structural determinants responsible for their broad direct and indirect pharmacological activities remain unclear. In this work, an LAAO from Bothrops jararacussu venom (BJu-LAAO) was purified and crystallized. The BJu-LAAO crystals belonged to space group P2(1), with unit-cell parameters a = 66.38, b = 72.19, c = 101.53 Å, β = 90.9°. The asymmetric unit contained two molecules and the structure was determined and partially refined at 3.0 Å resolution.

L-amino acid oxidases: properties and molecular mechanisms of action

During previous decade L-amino acid oxidases (LAAO) attracted the steady interest of researchers due to their poly functional effects on different biological systems. The review summarizes information concerning the sources, structure, phisico-chemical and catalytical properties of LAAO which exhibit antibacterial, antifungal, antiprotozoal, antiviral effects as well as the ambiguous action on platelet aggregation. Special attention is devoted to the elucidation of molecular mechanisms of LAAO action. It is proposed that the unique properties of LAAO are based on their catalytic reaction, which causes the decrease of L-amino acid levels, including the essential amino acids and formation of hydrogen peroxide. The action of liberated H2O2 on cells involves the synthesis of oxygen reactive species and the development of necrotic and apoptotic pathways of cell death. The presence of carbohydrate moieties in LAAO molecules promotes their attachment to cell's surface and creation of high H2O2 local concentrations. The wide range of LAAO biological effects is undoubtedly connected with their important functional roles in the organism. In particular, it was shown that in the mice brain the LAAO-catalyzed reaction is the single pathway of L-lysine degradation, while in the mice milk LAAO carry out the antibacterial effect and in human leucocytes LAAO take part in fulfilling their defending role. Protector action may be also attributed to the oxidases from the other numerous sources: microscopic fungi, snake venoms and sea inhabitants.

Identification of antibacterial mechanism of L-amino acid oxidase derived from Trichoderma harzianum ETS 323

Although L-amino oxidase (LAAO; EC 1.4.3.2) has been reported to be a potent antibacterial agent, the mechanism responsible for its antibacterial activity has not been identified. The present study aimed to identify the mechanism responsible for the antibacterial activity of Th-LAAO, an LAAO recently isolated from the extracellular proteins of Trichoderma harzianum ETS 323, at the same time as elucidating the nature of this enzyme. The results obtained indicate that the enzyme activity and structure of Th-LAAO are stable at pH 6-8 and less stable at both pH 4-5.5 and pH 9. At pH 7.0, the optimum temperature for Th-LAAO was found to be 40 °C, comprising the temperature at which enzymatic activity is greatest, with enzymatic activity deceasing with further increases in temperature as a result of thermal denaturation of the enzyme, leading to partial denaturation at 50 °C. The results obtained by confocal microscopy and flow cytometry indicate that Th-LAAO interacts with bacteria to cause membrane permeabilization, and this interaction may be promoted by the amphipathic sequence in Th-LAAO and other cytotoxic LAAOs located at the N-terminus. The findings of increased exogenous H(2) O(2) production and reactive oxidative species accumulation in Th-LAAO-treated bacteria indicate that reactive oxidative species accumulation may trigger forms of cell damage, including lipid peroxidation and DNA strand breakage that results in bacterial growth inhibition. Taken together, the results indicate that the processes of bacterial interaction, membrane permeabilization and H(2)O(2) production are involved in the mechanism responsible for the antibacterial activity of Th-LAAO.

The serum of rabbitfish (Siganus oramin) has antimicrobial activity to some pathogenic organisms and a novel serum L-amino acid oxidase is isolated

The serum of rabbitfish (Siganus oramin) has been confirmed previously to have killing effect to Cryptocaryon irritans, an important marine ciliate protozoan that causes a disease referred to as "marine white spot disease". Herein, we find the serum of the rabbitfish also shows antibacterial activity against both gram-positive and gram-negative bacteria and has killing effect on two other parasites: Trypanosoma brucei brucei, Ichthyophthirius multifiliis. Results of scanning electron microscopy indicated that after treating with rabbitfish serum, the surface of the Staphylococcus aureus was wrinkled and pores were formed on the surface of Escherichia coli. Serum of the rabbitfish possesses a strong killing effect to Ichthyophthirius multifiliis in vitro, causing a similar effect as to C. irritans. The serum of rabbitfish also showed strong killing effect to T. b. brucei in vitro, with the minimus trypanocidal titre (MTT) only to be 1.5% in 1 h. Results of laser confocal fluorescence microscopy indicated that rabbitfish serum could also induce cell rupture of T. b. brucei. A novel antimicrobial protein (SR-LAAO) was isolated from the serum of rabbitfish by using ultrafiltration, reversed phase high performance liquid chromatography (RP-HPLC) and Native polyacrylamide gel electrophoresis (Native-PAGE). Results of gel overlay assay showed that the protein could act alone to inhibit the growth of S. aureus and E. coli. Results of western blot and automated Edman degradation showed that it was the same as the antiparasitic protein (APP) reported before to have killing effect on C. irritans. Full length cDNA sequence of the SR-LAAO was cloned. BLAST research suggested that the cDNA of SR-LAAO has a close similarity with a number of L-amino acid oxidases (LAAOs) and possesses two conserved motifs that exist in LAAOs. Combined, these results demonstrate that this protein which has antimicrobial activity to some pathogenic organisms was a novel LAAO found in the serum of rabbitfish. Immunohistochemical analysis demonstrated tissue specific expression and localization of SR-LAAO in the spleen, kidney, gill and blood of the rabbitfish, but was not found in other tissues. These results suggest that this protein may contribute considerably to the host non-specific immune defense mechanism to combat microbes of the rabbitfish and has the potency for using in future drug development.

Antibacterial action of a heat-stable form of L-amino acid oxidase isolated from king cobra (Ophiophagus hannah) venom

The major l-amino acid oxidase (LAAO, EC 1.4.3.2) of king cobra (Ophiophagus hannah) venom is known to be an unusual form of snake venom LAAO as it possesses unique structural features and unusual thermal stability. The antibacterial effects of king cobra venom LAAO were tested against several strains of clinical isolates including Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli using broth microdilution assay. For comparison, the antibacterial effects of several antibiotics (cefotaxime, kanamycin, tetracycline, vancomycin and penicillin) were also examined using the same conditions. King cobra venom LAAO was very effective in inhibiting the two Gram-positive bacteria (S. aureus and S. epidermidis) tested, with minimum inhibitory concentration (MIC) of 0.78μg/mL (0.006μM) and 1.56μg/mL (0.012μM) against S. aureus and S. epidermidis, respectively. The MICs are comparable to the MICs of the antibiotics tested, on a weight basis. However, the LAAO was only moderately effective against three Gram-negative bacteria tested (P. aeruginosa, K. pneumoniae and E. coli), with MIC ranges from 25 to 50μg/mL (0.2-0.4μM). Catalase at the concentration of 1mg/mL abolished the antibacterial effect of LAAO, indicating that the antibacterial effect of the enzyme involves generation of hydrogen peroxide. Binding studies indicated that king cobra venom LAAO binds strongly to the Gram-positive S. aureus and S. epidermidis, but less strongly to the Gram-negative E. coli and P. aeruginosa, indicating that specific binding to bacteria is important for the potent antibacterial activity of the enzyme.

Discovery of serum L-amino acid oxidase in the rockfish Sebastes schlegeli: isolation and biochemical characterization

Fish have a complex innate defense mechanism against microbial invasion. In particular, epidermal mucus and serum in fish play important roles in innate immunity and contain a variety of bioactive substances such as complements, lectins and lysozymes, involved in host defense. Recently, L-amino acid oxidases (LAOs) with antibacterial activity were isolated from the skin and/or gill mucous secretions of rockfish, great sculpin and flounder, and were identified to be a novel type of antibacterial protein in the integument of fish. In the present study, we found LAO activity in the serum of rockfish Sebastes schlegeli. The LAO was isolated from the serum by sequential column chromatography of Con-A lectin affinity chromatography, anion exchange HPLC, hydroxyapatite HPLC and gel filtration HPLC, and characterized. The LAO (a molecular mass of 160 kDa) comprised subunits with a molecular mass of 53 kDa and showed strict substrate specificity, catalyzing only L-lysine with Km 0.37 mM and kcat 57.1s(-1). The serum LAO exhibited a broad antibacterial activity against Gram positive and negative bacteria, most potently against Aeromonas hydrophila and Aeromonas salmonicida with a minimum inhibitory concentration of 0.078 μg/mL. This is the first report of LAO in the serum of fish and its involvement in innate immunity in the rockfish body.