Exploration of antimicrobial and anticancer activities of L-amino acid oxidase from Egyptian Naja haje venom

Hepatocellular carcinoma and bacterial resistance are major health burdens nowadays. Thus, providing new therapies that overcome that resistance is of great interest, particularly those derived from nature rather than chemotherapeutics to avoid cytotoxicity on normal cells. Venomous animals are among the natural sources that assisted in the discovery of novel therapeutic regimens. L-amino acid oxidase Nh-LAAO (140 kDa), purified from Egyptian Naja haje venom by a successive two-step chromatography protocol, has an optimal pH and temperature of 8 and 37 °C. Under standard assay conditions, Nh-LAAO exhibited the highest specificity toward L-Arg, L-Met and L-Leu, with Km and Vmax values of 3.5 mM and 10.4 μmol/min/ml, respectively. Among the metal ions, Ca+2, Na+, and K+ ions are activators, whereas Fe+2 inhibited LAAO activity. PMSF and EDTA slightly inhibited the Nh-LAAO activity. In addition, Nh-LAAO showed antibacterial and antifungal activities, particularly against Gentamicin-resistant P. aeruginosa and E. coli strains with MIC of 18 ± 2 μg/ml, as well as F. proliferatum and A. parasiticus among the selected human pathogenic strains. Furthermore, Nh-LAAO exhibited anti-proliferative activity against cancer HepG2 and Huh7 cells with IC50 of 79.37 and 60.11 μg/ml, respectively, with no detectable effect on normal WI-38 cells. Consequently, the apoptosis % of the HepG2 and Huh7 cells were 12 ± 1 and 34.5 ± 2.5 %, respectively, upon Nh-LAAO treatment. Further, the Nh-LAAO arrested the HepG2 and Huh7 cell cycles in the G0/G1 phase. Thus, the powerful selective cytotoxicity of L-amino acid oxidase opens up the possibility as a good candidate for clinical cancer therapy.

Bothrops snake venom L-amino acid oxidases impair biofilm formation of clinically relevant bacteria

The present work addressed the abilities of two L-amino acid oxidases isolated from Bothrops moojeni (BmooLAAO-I) and Bothrops jararacussu (BjussuLAAO-II) snake venoms to control the growth and prevent the biofilm formation of clinically relevant bacterial pathogens. Upon S. aureus (ATCC BAA44) and S. aureus (clinical isolates), BmooLAAO-I (MIC = 0.12 and 0.24 μg/mL, respectively) and BjussuLAAO-II (MIC = 0.15 μg/mL) showed a potent bacteriostatic effect. Against E. coli (ATCC BAA198) and E. coli (clinical isolates), BmooLAAO-I (MIC = 15.6 and 62.5 μg/mL, respectively) and BjussuLAAO-II (MIC = 4.88 and 9.76 μg/mL, respectively) presented a lower extent effect. Also, BmooLAAO-I (MICB50 = 0.195 μg/mL) and BjussuLAAO-II (MICB50 = 0.39 μg/mL) inhibited the biofilm formation of S. aureus (clinical isolates) in 88% and 89%, respectively, and in 89% and 53% of E. coli (clinical isolates). Moreover, scanning electron microscopy confirmed that the toxins affected bacterial morphology by increasing the roughness of the cell surface and inhibited the biofilm formation. Furthermore, analysis of the tridimensional structures of the toxins showed that the surface-charge distribution presents a remarkable positive region close to the glycosylation motif, which is more pronounced in BmooLAAO-I than BjussuLAAO-II. This region may assist the interaction with bacterial and biofilm surfaces. Collectively, our findings propose that venom-derived antibiofilm agents are promising biotechnological tools which could provide novel strategies for biofilm-associated infections.

Cobra (Naja naja) venom L-amino acid oxidase (NNLAAO70) induces apoptosis and secondary necrosis in human lung epithelial cancer cells

Snake venom L-amino acid oxidases (LAAOs) are flavoenzymes with diverse physiological and pharmacological effects. These enzymes are found to showcase anticoagulant, antiplatelet, cytotoxicity and other biological effects in bite victims. However, the exact mechanism through which they exhibit several biological properties is not yet fully understood. The current study focussed on the purification of cobra venom LAAO and the functional characterization of purified LAAO. A novel L-amino acid oxidase NNLAAO70 with a molecular weight ~70 kDa was purified from the venom of an Indian spectacled cobra (Naja naja). NNLAAO70 showed high substrate specificity for L-His, L-Leu, and L-Arg during its LAAO activity. It inhibited adenosine di-phosphate (ADP) and collagen-induced platelet aggregation process in a dosedependent manner. About 60% inhibition of collagen-induced and 40% inhibition of ADP-induced platelet aggregation was observed with a 40 μg/ml dose of NNLAAO70. NNLAAO70 exhibited bactericidal activity on Bacillus subtilis, Escherichia coli, Bacillus megaterium, and Pseudomonas fluorescens. NNLAAO70 also showed cytotoxicity on A549 cells in vitro. It showed severe bactericidal activity on P. fluorescens and lysed 55% of cells. NNLAAO70 also exhibited drastic cytotoxicity on A549 cells. At 1 lg/ml dosage, it demonstrated a 60% reduction in A549 viability and induced apoptosis upon 24-h incubation. H2O2 released during oxidative deamination reactions played a major role in NNLAAO70-induced cytotoxicity. NNLAAO70 significantly increased intracellular reactive oxygen species (ROS) levels in A549 cells by six fold when compared to untreated cells. Oxidative stress-mediated cell injury is the primary cause of NNLAAO70-induced apoptosis in A549 cells and prolonged oxidative stress caused DNA fragmentation and activated cellular secondary necrosis.

Exosome Liberation by Human Neutrophils under L-Amino Acid Oxidase of Calloselasma rhodostoma Venom Action

L-Amino acid oxidase (LAAO) is an enzyme found in snake venom that has multifaceted effects, including the generation of hydrogen peroxide (H2O2) during oxidative reactions, leading to various biological and pharmacological outcomes such as apoptosis, cytotoxicity, modulation of platelet aggregation, hemorrhage, and neutrophil activation. Human neutrophils respond to LAAO by enhancing chemotaxis, and phagocytosis, and releasing reactive oxygen species (ROS) and pro-inflammatory mediators. Exosomes cellular nanovesicles play vital roles in intercellular communication, including immune responses. This study investigates the impact of Calloselasma rhodostoma snake venom-derived LAAO (Cr-LAAO) on human neutrophil exosome release, including activation patterns, exosome formation, and content. Neutrophils isolated from healthy donors were stimulated with Cr-LAAO (100 μg/mL) for 3 h, followed by exosome isolation and analysis. Results show that Cr-LAAO induces the release of exosomes with distinct protein content compared to the negative control. Proteomic analysis reveals proteins related to the regulation of immune responses and blood coagulation. This study uncovers Cr-LAAO's ability to activate human neutrophils, leading to exosome release and facilitating intercellular communication, offering insights into potential therapeutic approaches for inflammatory and immunological disorders.

BjussuLAAO-II, an l-amino acid oxidase from Bothrops jararacussu snake venom, impairs Toxoplasma gondii infection in human trophoblast cells and villous explants from the third trimester of pregnancy

One-third of the world's population is estimated to be affected by toxoplasmosis. Pregnancy-related Toxoplasma gondii infection can cause vertical transmission, infect the fetus, and cause miscarriage, stillbirth, and fetal death. The current study showed that both human trophoblast cells (BeWo lineage) and human explant villous were resistant to T. gondii infection after incubation with BjussuLAAO-II, an l-amino acid oxidase isolated from Bothrops jararacussu. Almost 90% of the parasite's ability to proliferate in BeWo cells was decreased by the toxin at 1.56 μg/mL and showed an irreversible anti-T. gondii effect. Also, BjussuLAAO-II impaired the key events of adhesion and invasion of T. gondii tachyzoites in BeWo cells. BjussuLAAO-II antiparasitic properties were associated with the intracellular production of reactive oxygen species and hydrogen peroxide, since the presence of catalase restored the parasite's growth and invasion. In addition, T. gondii growth in human villous explants was decreased to approximately 51% by the toxin treatment at 12.5 μg/mL. Furthermore, BjussuLAAO-II treatment altered IL-6, IL-8, IL-10 and MIF cytokines levels, assuming a pro-inflammatory profile in the control of T. gondii infection. This study contributes to the potential use of a snake venom l-amino acid oxidase for the development of agents against congenital toxoplasmosis and the discovery of new targets in parasites and host cells.

Reactive oxygen species-dependent-NLRP3 inflammasome activation in human neutrophils induced by l-amino acid oxidase derived from Calloselasma rhodostoma venom

l-Amino acid oxidase isolated from Calloselasma rhodostoma (Cr-LAAO) snake venom is a potent stimulus for neutrophil activation and production of inflammatory mediators, contributing to local inflammatory effects in victims of envenoming. Cr-LAAO triggered the activation of nicotinamide adenine dinucleotide phosphatase (NADPH) oxidase complex and protein kinase C (PKC)-α signaling protein for reactive oxygen species (ROS) production. This study aims to evaluate the ROS participation in the NLRP3 inflammasome complex activation in human neutrophil. Human neutrophils were isolated and stimulated for 1 or 2 h with RPMI (negative control), LPS (1 μg/mL, positive control) or Cr-LAAO (50 μg/mL). The neutrophil transcriptome was examined using the microarray technique, and RT-qPCR for confirmation of gene expression. Immunofluorescence assays for NLRP3, caspase-1, IL-1β and GSDMD proteins was performed by Western blot in the presence and/or absence of Apocynin, an inhibitor of NADPH oxidase. IL-1β release was also detected in the presence and/or absence of NLRP3, caspase-1 and NADPH oxidase inhibitors. Results showed that Cr-LAAO upregulated the expression of genes that participate in the NADPH oxidase complex formation and inflammasome assembly. NLRP3 was activated and accumulated in the cytosol forming punctas, indicating its activation. Gasdermin D was not cleaved but lactate dehydrogenase was released. Furthermore, ROS inhibition decreased the expression of NLRP3 inflammasome complex proteins, as observed by protein expression in the presence and/or absence of apocynin, an NADPH oxidase inhibitor. IL-1β was also released, and pharmacological inhibition of NLRP3, caspase-1, and ROS reduced the amount of released cytokine. This is the first report demonstrating the activation of the NLRP3 inflammasome complex via ROS generation by Cr-LAAO, which may lead to the development of local inflammatory effects observed in snakebite victims.

Characterization of L-amino Acid Oxidase Derived from Crotalus adamanteus Venom: Procoagulant and Anticoagulant Activities

Snake venom enzymes of the L-amino acid oxidase (LAAO) class are responsible for tissue hemorrhage, edema, and derangement of platelet function. However, what role, if any, these flavoenzymes play in altering plasmatic coagulation have not been well defined. Using coagulation kinetomic analyses (thrombelastograph-based), it was determined that the LAAO derived from Crotalus adamanteus venom displayed a procoagulant activity associated with weak clot strength (no factor XIII activation) similar to thrombin-like enzymes. The procoagulant activity was not modified in the presence of reduced glutathione, demonstrating that the procoagulant activity was likely due to deamination, and not hydrogen peroxide generation by the LAAO. Further, unlike the raw venom of the same species, the purified LAAO was not inhibited by carbon monoxide releasing molecule-2 (CORM-2). Lastly, exposure of the enzyme to phenylmethylsulfonyl fluoride (PMSF) resulted in the LAAO expressing anticoagulant activity, preventing contact activation generated thrombin from forming a clot. In sum, this investigation for the first time characterized the LAAO of a snake venom as both a fibrinogen polymerizing and an anticoagulant enzyme acting via oxidative deamination and not proteolysis as is the case with thrombin-like enzymes (e.g., serine proteases). Using this thrombelastographic approach, future investigation of purified enzymes can define their biochemical nature.

Molecules and Mechanisms Underlying the Antimicrobial Activity of Escapin, an l-Amino Acid Oxidase from the Ink of Sea Hares

Many marine animals use chemicals to defend themselves and their eggs from predators. Beyond their ecologically relevant functions, these chemicals may also have properties that make them beneficial for humans, including biomedical and industrial applications. For example, some chemical defenses are also powerful antimicrobial or antitumor agents with relevance to human health and disease. One such chemical defense, escapin, an l-amino acid oxidase in the defensive ink of the sea hare Aplysia californica, and related proteins have been investigated for their biomedical properties. This review details our current understanding of escapin's antimicrobial activity, including the array of molecules generated by escapin's oxidation of its major substrates, l-lysine and l-arginine, and mechanisms underlying these molecules' bactericidal and bacteriostatic effects on planktonic cells and the prevention of formation and removal of bacterial biofilms. Models of escapin's effects are presented, and future directions are proposed.

Comprehensive Snake Venomics of the Okinawa Habu Pit Viper, Protobothrops flavoviridis, by Complementary Mass Spectrometry-Guided Approaches

The Asian world is home to a multitude of venomous and dangerous snakes, which are used to induce various medical effects in the preparation of traditional snake tinctures and alcoholics, like the Japanese snake wine, named Habushu. The aim of this work was to perform the first quantitative proteomic analysis of the Protobothrops flavoviridis pit viper venom. Accordingly, the venom was analyzed by complimentary bottom-up and top-down mass spectrometry techniques. The mass spectrometry-based snake venomics approach revealed that more than half of the venom is composed of different phospholipases A2 (PLA₂). The combination of this approach and an intact mass profiling led to the identification of the three main Habu PLA₂s. Furthermore, nearly one-third of the total venom consists of snake venom metalloproteinases and disintegrins, and several minor represented toxin families were detected: C-type lectin-like proteins (CTL), cysteine-rich secretory proteins (CRISP), snake venom serine proteases (svSP), l-amino acid oxidases (LAAO), phosphodiesterase (PDE) and 5'-nucleotidase. Finally, the venom of P. flavoviridis contains certain bradykinin-potentiating peptides and related peptides, like the svMP inhibitors, pEKW, pEQW, pEEW and pENW. In preliminary MTT cytotoxicity assays, the highest cancerous-cytotoxicity of crude venom was measured against human neuroblastoma SH-SY5Y cells and shows disintegrin-like effects in some fractions.

Cytotoxic, Anti-Proliferative and Apoptosis Activity of l-Amino Acid Oxidase from Malaysian Cryptelytrops purpureomaculatus (CP-LAAO) Venom on Human Colon Cancer Cells

The aim of this study is to investigate the potential anti-cancer activity of l-amino acid oxidase (CP-LAAO) purified from the venom of Cryptelytrops purpureomaculatus on SW480 and SW620 human colon cancer cells. Mass spectrometry guided purification was able to identify and purify CP-LAAO. Amino acid variations identified from the partial protein sequence of CP-LAAO may suggest novel variants of these proteins. The activity of the purified CP-LAAO was confirmed with o-phenyldiamine (OPD)-based spectrophotometric assay. CP-LAAO demonstrated time- and dose-dependent cytotoxic activity and the EC₅₀ value was determined at 13 µg/mL for both SW480 and SW620 cells. Significant increase of caspase-3 activity, reduction of Bcl-2 levels, as well as morphological changes consistent with apoptosis were demonstrated by CP-LAAO. Overall, these data provide evidence on the potential anti-cancer activity of CP-LAAO from the venom of Malaysian C. purpureomaculatus for therapeutic intervention of human colon cancer.

Isolation and pharmacological characterization of a new cytotoxic L-amino acid oxidase from Bungarus multicinctus snake venom

ETHNOPHARMACOLOGICAL RELEVANCE

Bungarus multicinctus snake belongs to Elapidae family and is widely distributed in southern China. It is widely used in traditional Chinese medicine with the effect of dispelling wind and removing obstruction in the meridians. Moreover, it is also as a chief ingredient of many polyherbal formulations for the treatment of cancer.

AIM OF THE STUDY

To evaluate the antitumor activity of Bungarus multicinctus snake venom components and isolate, characterize the most effective anti-tumor component of Bungarus multicinctus snake venom.

MATERIALS AND METHODS

The in vitro antitumor activity of Bungarus multicinctus venom components was detected by cytotoxicity assay and cell apoptosis assay. A unique LAAO from Bungarus multicinctus venom named as BM-Apotxin was isolated and characterized by Sephadex G-75 gel filtration, Sephadex G-25 desalting, Q ion-exchange chromatography and subsequent amino acids sequence determination. The LAAO activity and enzyme kinetics of BM-Apotxin was detected by microplate assay.

RESULTS

BM-Apotxin, a 65KDa glycoprotein, which contributed to the most anti-tumor effects of Bungarus multicinctus venom. BM-Apotxin can selectively kill tumor cells, with less cytotoxicity to the normal cells. BM-Apotxin is an L-amino acid oxidase (LAAO) with high sequence identity to other snake venom LAAOs. Its anti-tumor activity is mainly due to the hydrogen peroxide produced from LAAO oxidation. But the catalase did not reverse its anti-tumor effect completely. Like other snake venom LAAOs, BM-Apotxin can oxidize many L amino acids, not D amino acids. The optimum substrate for BM-Apotxin is L-Phe. Moreover, BM-Apotxin deglycosylation can significantly reduce the LAAO activity and anti-tumor activity of BM-Apotxin.

CONCLUSION

This study will facilitate the study on anti-tumor mechanism of snake venom and drug development based on Bungarus multicinctus venom.

Isolation, characterization and screening of the in vitro cytotoxic activity of a novel L-amino acid oxidase (LAAOcdt) from Crotalus durissus terrificus venom on human cancer cell lines

An L-amino acid oxidase (LAAOcdt) from Crotalus durissus terrificus venom was purified to homogeneity in a two-step procedure using molecular exclusion on Sephadex G-75, followed by Phenyl Sepharose FF chromatography. The molecular mass of the purified enzyme was 113 kDa, as determined by SDS-PAGE under reducing conditions. LAAOcdt showed amino acid homology to other L-amino acid oxidases isolated from different snake venoms. The comparative analysis of the internal peptide sequences of the NNPGILEYPVKPSEEGK fragments by LC-MS/MS spectrometry revealed 100% identity with C. durissus cumanensis LAAO. The purified protein catalyzed the oxidative deamination of L-amino acids, and the most specific substrates were L-Tyr and L-Phe. The enzyme presented optimum activity at pH 7.4 and at 44 °C. LAAOcdt also showed hemolytic activity (0.6-20 μg/μL) and induced both the formation plasma clots (5-100 μg/μL) and platelet aggregation (2.5 × 10(-3), 5.0 × 10(-3) and 10 × 10(-3) μg/mL), as well as bactericidal activity (2.5-10 μg/μL) against Staphylococcus aureus. Moreover, LAAOcdt exhibited cytotoxicity in distinct cancer cell lines, which presented a heterogeneous response profile. The mean IC50 value was 10.5 μg/mL. Glioma and pancreatic carcinoma cells were the most sensitive cell lines; they showed mean IC50 values of 7.2 μg/mL and 7.4 μg/mL, respectively. The exposure of the drug-sensitive cells to LAAOcdt for 24 h upregulated activated p-H2AX and efficiently decreased P42/P44 (ERK) activation in glioma cells (HCB151), which suggested an anti-proliferative effect. In addition, increased p21 expression was observed in SiHa cells, which showed a resistant phenotype. On the other hand, the flow cytometry and immunoblotting analyses showed that the enzyme did not induce cancer cell apoptosis. These results suggest that another cell death mechanism might contribute to the LAAOcdt-induced cytotoxicity. Taken together, this work may help to elucidate the function and structure of LAAOcdt by providing the basis for further investigations on its efficacy in cancer treatment.

Apoptosis induction in human breast cancer (MCF-7) cells by a novel venom L-amino acid oxidase (Rusvinoxidase) is independent of its enzymatic activity and is accompanied by caspase-7 activation and reactive oxygen species production

We report the elucidation of a mechanism of apoptosis induction in breast cancer (MCF-7) cells by an L-amino acid oxidase (LAAO), Rusvinoxidase, purified from the venom of Daboia russelii russelii. Peptide mass fingerprinting analysis of Rusvinoxidase, an acidic monomeric glycoprotein with a mass of ~57 kDa, confirmed its identity as snake venom LAAO. The enzymatic activity of Rusvinoxidase was completely abolished after two cycles of freezing and thawing; however, its cytotoxicity toward MCF-7 cells remained unaffected. Dose- and time-dependent induction of apoptosis by Rusvinoxidase on MCF-7 cells was evident from changes in cell morphology, cell membrane integrity, shrinkage of cells and apoptotic body formation accompanied by DNA fragmentation. Rusvinoxidase induced apoptosis in MCF-7 cells by both the extrinsic (death-receptor) and intrinsic (mitochondrial) signaling pathways. The former pathway of apoptosis operated through activation of caspase-8 that subsequently activated caspase-7 but not caspase-3. Rusvinoxidase-induced intrinsic pathway of apoptosis was accompanied by a time-dependent depolarization of the mitochondrial membrane through the generation of reactive oxygen species, followed by a decrease in cellular glutathione content and catalase activity, and down-regulation of expression of anti-apoptotic proteins Bcl-XL and heat-shock proteins (HSP-90 and HSP-70). Rusvinoxidase treatment resulted in increase of the pro-apoptotic protein Bax, subsequently leading to the release of cytochrome c from mitochondria to the cytosol and activating caspase-9, which in turn stimulated effector caspase-7. Rusvinoxidase at a dose of 4 mg/kg was non-toxic in mice, indicating that it may be useful as a model for the development of peptide-based anticancer drugs.

Snake venom L-amino acid oxidases: trends in pharmacology and biochemistry

L-amino acid oxidases are enzymes found in several organisms, including venoms of snakes, where they contribute to the toxicity of ophidian envenomation. Their toxicity is primarily due to enzymatic activity, but other mechanisms have been proposed recently which require further investigation. L-amino acid oxidases exert biological and pharmacological effects, including actions on platelet aggregation and the induction of apoptosis, hemorrhage, and cytotoxicity. These proteins present a high biotechnological potential for the development of antimicrobial, antitumor, and antiprotozoan agents. This review provides an overview of the biochemical properties and pharmacological effects of snake venom L-amino acid oxidases, their structure/activity relationship, and supposed mechanisms of action described so far.

[Snake Venom L-Amino Acid Oxidases potential biomedical applications]

L-amino acid oxidases (LAAOs) are flavoenzymes widely found in several organisms, including venoms snakes, where they contribute to the toxicity of ophidian envenomation. Their toxicity is primarily due to enzymatic activity, but other mechanisms have been proposed recently which require further investigation. LAAOs exert biological and pharmacological effects, including actions on platelet aggregation and the induction of apoptosis, hemorrhage and cytotoxicity. These proteins present a high biotechnological potentialfor the development of antimicrobial, antitumor and antiprotozoan agents. This review summarizes the biochemical properties, structural characteristics and various biological functions of snake venoms' LAAO. Furthermore, the putative mechanisms of action, were well detailed.

Evaluation of an antimicrobial L-amino acid oxidase and peptide derivatives from Bothropoides mattogrosensis pitviper venom

Healthcare-associated infections (HAIs) are causes of mortality and morbidity worldwide. The prevalence of bacterial resistance to common antibiotics has increased in recent years, highlighting the need to develop novel alternatives for controlling these pathogens. Pitviper venoms are composed of a multifaceted mixture of peptides, proteins and inorganic components. L-amino oxidase (LAO) is a multifunctional enzyme that is able to develop different activities including antibacterial activity. In this study a novel LAO from Bothrops mattogrosensis (BmLAO) was isolated and biochemically characterized. Partial enzyme sequence showed full identity to Bothrops pauloensis LAO. Moreover, LAO here isolated showed remarkable antibacterial activity against Gram-positive and -negative bacteria, clearly suggesting a secondary protective function. Otherwise, no cytotoxic activities against macrophages and erythrocytes were observed. Finally, some LAO fragments (BmLAO-f1, BmLAO-f2 and BmLAO-f3) were synthesized and further evaluated, also showing enhanced antimicrobial activity. Peptide fragments, which are the key residues involved in antimicrobial activity, were also structurally studied by using theoretical models. The fragments reported here may be promising candidates in the rational design of new antibiotics that could be used to control resistant microorganisms.

Cloning, characterization and mutagenesis of Russell's viper venom L-amino acid oxidase: Insights into its catalytic mechanism

To investigate the structure-function relationships and geographic variations of L-amino acid oxidase (LAAO) from Daboia venoms, a single LAAO (designated as DrLAO) was purified from eastern Indian Daboia russelii venom and characterized. The purified DrLAO showed subunit molecular mass of 60-64kDa; its N-terminal sequence (1-20) was identical to those of several true viper LAAOs. Its preferred substrates were hydrophobic l-amino acids and the kinetic specificities were ordered as follows: Phe, Tyr, Met, Leu, and Trp. Enzyme assay and Western blotting showed that the venom LAAO contents of D. russelii were higher than those of Daboia siamensis. DrLAO dose-dependently inhibited ADP- and collagen-induced platelet aggregation with IC(50) values of 0.27 and 0.82μM, respectively. Apparently, DrLAO may synergize with other venom components to prolong and enhance bleeding symptoms after Daboia envenoming. The full sequence of DrLAO was deduced from its cDNA sequence and then confirmed by peptide mass fingerprinting. Molecular phylogenetic analysis revealed that SV-LAAO family members could be differentiated not only by snake taxonomy but also by the variations at position 223, and they divided into H223, S223, N223, and D223 subclasses. We have further prepared recombinant DrLAO and mutants by the Pichia expression system. Mutagenic analyses of DrLAO His223 revealed that this residue bound substrates instead of serving as an essential base in the catalytic steps. Our results suggest a direct hydride transfer from substrate to FAD as the mechanism for SV-LAAOs.

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.

Gene expression and distribution of antibacterial L-amino acid oxidase in the rockfish Sebastes schlegeli

Antibacterial factors in the epidermal mucus of fish have a potential importance in the first line of the host defense response to bacterial pathogens. We previously isolated a novel antibacterial protein termed SSAP (Sebastes schlegeli antibacterial protein) from the skin mucus of the rockfish S. schlegeli and identified it as a new member of the L-amino acid oxidase (LAO) family. In the present study, the localization of SSAP in S. schlegeli was investigated by reverse transcription (RT)-PCR, quantitative real time RT-PCR, Western blotting and measurements of LAO and antibacterial activities. SSAP mRNA was expressed dominantly in skin and gill and weakly in ovary or kidney as shown by RT-PCR and real time RT-PCR. The quantity of SSAP mRNA in skin varied among the individuals, ranging from 1.1 to 13.9 ng microg(-1) total RNA, although no relationship was found between the size of fish and gene expression. SSAP was exclusively detected in skin and gill by Western blotting using a specific anti-SSAP antiserum. In addition, the extracts of both tissues apparently showed LAO activity and antibacterial activity against Photobacterium damselae subsp. piscicida. This study demonstrates that SSAP is predominantly synthesized in skin and gill and probably functions as an antibacterial LAO in both tissues.

Molecular characterization of l-amino acid oxidase from king cobra venom

An L-amino acid oxidase from Ophiophagus hannah snake venom (Oh-LAAO) was purified by successive gel filtration, ion-exchange and heparin chromatography. Oh-LAAO did not induce platelet aggregation; however, it had potent inhibitory activity on platelet aggregation induced by ADP and U46619, but showed no effect on platelet aggregation induced by thrombin, mucetin, ristocetin and stejnulxin. By RT-PCR and 5'-RACE methods, the complete Oh-LAAO cDNA was cloned from the venom gland total RNA preparations. The cDNA sequence contains an open-reading frame (ORF) of 1476-bp, which encodes a protein of 491 amino acids comprising a signal peptide of 25 amino acids and 466-residue mature protein. The predicted protein sequence of Oh-LAAO was confirmed by N-terminal and trypsin-digested internal peptides sequencing together with peptide mass fingerprinting. cDNAs encoding for ORF of LAAOs from Bungarus fasciatus and B. multicinctus were cloned and reported in this study. In addition, partial cDNA encoding for Naja atra LAAO was also reported. Oh-LAAO shared approximately 50% protein sequence identity with other known snake venom LAAOs. Phylogenetic analysis indicated that Oh-LAAO is evolutionary distant to other snake venom LAAOs.

Biochemical and functional characterization of an L-amino acid oxidase isolated from Bothrops pirajai snake venom

In this work we describe the isolation of a new l-amino acid oxidase (LAAO) referred to as BpirLAAO-I from Bothrops pirajai snake venom, which was highly purified using a combination of molecular exclusion, affinity, and hydrophobic chromatography steps. BpirLAAO-I homodimeric acid glycoprotein (approximate Mr and pI of 130,000 and 4.9, respectively) displays high specificity toward hydrophobic/aromatic amino acids, while deglycosylation does not alter its enzymatic activity. The N-terminal LAAO sequence of its first 49 amino acids presented a high similarity between a amino acid sequence with other LAAOs from: Bothrops spp., Crotalus spp., Calloselasma rhodostoma, Agkistrodon spp., Trimeresurus spp., Pseudechis australis, Oxyuranus scutellatus, and Notechis scutatus. BpirLAAO-I induces time-dependent platelet aggregation, mouse paw edema, cytotoxic activity against Escherichia coli, Pseudomonas aeruginosa, Leishmania sp., and tumor cells, and also a typical fago (M13mp18) DNA fragmentation. Platelet aggregation, leishmanicidal and antitumoral activities were reduced by catalase. Thus, BpirLAAO-I is a multifunctional protein with promising biotechnological and medical applications.

Mechanisms of cell death induction by L-amino acid oxidase, a major component of ophidian venom

L-amino acid oxidase (LAAO) from the Malayan pit viper induces both necrosis and apoptosis in Jurkat cells. Cell death by necrosis is attributed to H2O2 produced by oxidation of alpha-amino acids. In the presence of catalase that effectively scavenges H2O2, a switch to apoptosis is observed. The major factors contributing to apoptosis are proposed to be: (i) generation of toxic intermediates from fetal calf serum (ii) binding and internalization of LAAO. The latter process appears to be mediated by the glycan moiety of the enzyme as desialylation reduces cytotoxicity. D-amino acid oxidase (DAAO), which catalyzes the same reaction as LAAO but lacks glycosylation, triggers necrosis as a consequence of H2O2 production but not apoptosis in the presence of catalase. Thus induction of cell death by LAAO appears to involve both the generation of H2O2 and the molecular interaction of the glycan moiety of the enzyme with structures at the cell surface.

Cloning, characterization and expression of escapin, a broadly antimicrobial FAD-containing L-amino acid oxidase from ink of the sea hare Aplysia californica

A 60 kDa monomeric protein isolated from the defensive purple ink secretion of the sea hare Aplysia californica was cloned and sequenced, and is the first sea hare antimicrobial protein to be functionally expressed in E. coli. Sequence analysis suggested that this protein is a flavin-containing l-amino acid oxidase (LAAO), with one predicted potential glycosylation site, although the glycosylation could not be experimentally confirmed. This protein, which we call ;escapin', has high sequence similarity to several other gastropod proteins. Escapin was verified by NMR, mass spectroscopy and HPLC to have FAD as its flavin cofactor. Escapin's antimicrobial effects, bacteriostasis and bactericidal, were determined using a combination of two assays: (1) incubation of bacteria on solid media followed by assessment of inhibition by direct observation of zones of inhibition or by turbidity measurements; and (2) incubation of bacteria in liquid media followed by counting viable colonies after growing on agar plates. Native escapin inhibited the growth of Gram-positive and Gram-negative bacteria, including marine bacteria (Vibrio harveyii and Staphylococcus aureus) and pathogenic bacteria (Staphylococcus aureus, Streptococcus pyogenes and Pseudomonas aeruginosa). Escapin also inhibited the growth of yeast and fungi, with different efficacies. Escapin's antimicrobial activity was concentration dependent and did not decrease when stored for more than 5 months at room temperature. Escapin was bacteriostatic and not bactericidal in minimal media (e.g. salt media) with glucose, yeast extract, and a mixture of 20 amino acids each at 50 micromol l(-1), but was bactericidal in media enriched with Tryptone Peptone. Escapin was also strongly bactericidal in media with l-lysine at concentrations as low as 3 mmol l(-1) and slightly bactericidal in 50 mmol l(-1) l-arginine, but not in most other amino acids even at 50 mmol l(-1). Escapin had high oxidase activity (producing hydrogen peroxide) with either l-arginine or l-lysine as a substrate and little to no oxidase activity with other l-amino acids. Hydrogen peroxide alone (without escapin or amino acids) was strongly bacteriostatic but poorly bactericidal, similar in this respect to l-arginine but different from l-lysine in the presence of escapin. Together these results suggest that there are multiple mechanisms to escapin's antimicrobial effects, with bacteriostasis resulting largely or entirely from the effects of hydrogen peroxide produced by escapin's LAAO activity, but bactericidal effects resulting from lysine-dependent mechanisms not directly involving hydrogen peroxide. Recombinant escapin expressed in bacteria was also active against Gram-positive and Gram-negative bacteria, suggesting that glycosylation is not essential for antimicrobial activity.

Isolation of a new l-amino acid oxidase from Crotalus durissus cascavella venom

A novel l-amino acid oxidase (LAO) (Casca LAO) from Crotalus durissus cascavella venom was purified to a high degree of molecular homogeneity using a combination of molecular exclusion and ion-exchange chromatography system. The purified monomer of LAO presented a molecular mass of 68 kDa and pI estimated in 5.43, which were determined by two-dimensional electrophoresis. The 71st N-terminal amino acid sequence of the LAO from Crotalus durissus cascavella presented a high amino acid sequence similarities with other LAOs from Colloselasma rhosostoma, Crotalus adamanteus, Agkistrodon h. blomhoffi, Agkistrodon h. halys and Trimeresurus stejnegeri. LAO displayed a Michaelis-Menten behavior with a kilometer of 46.7 microM and an optimum pH for enzymatic activity of 6.5. Casca LAO induced a dose-dependent platelet aggregation, which was abolished by catalase and inhibited by indomethacin and aspirin. These results suggest that the production of H2O2 is involved in subsequent activation of inflammatory enzymes, such as thromboxane. Casca LAO also inhibited the bacterial growth of Gram-negative (Xanthomonas axonopodis pv passiflorae) and Gram-positive (S. mutans) strains. Electron microscopy assessments of both bacterial strains suggest that the hydrogen peroxide produced by LAO induce bacterial membrane rupture and consequently loss of cytoplasmatic content. This LAO exhibited a high antileishmanic activity against the promastigote of Leishmania amazonensis in vitro, its activity was dependent on the production of hydrogen peroxide, and the 50% inhibitory concentration was estimated in 2.39 microg/ml.