Recombinant expression and functional analysis of antimicrobial Siganus oraminl-amino acid oxidase using the Bac-to-Bac baculovirus expression system

Improvement of Heterologous Soluble Expression of L-amino Acid Oxidase Using Logistic Regression

Successful implementation of enzymes in practical application hinges on the development of efficient mass production techniques. However, in a heterologous expression system, the protein is often unable to fold correctly and, thus, forms inclusion bodies, resulting in the loss of its original activity. In this study, we present a new and more accurate model for predicting amino acids associated with an increased L-amino acid oxidase (LAO) solubility. Expressing LAO from Rhizoctonia solani in Escherichia coli and combining random mutagenesis and statistical logistic regression, we modified 108 amino acid residues by substituting hydrophobic amino acids with serine and hydrophilic amino acids with alanine. Our results indicated that specific mutations in Euclidean distance, glycine, methionine, and secondary structure increased LAO expression. Furthermore, repeated mutations were performed for LAO based on logistic regression models. The mutated LAO displayed a significantly increased solubility, with the 6-point and 58-point mutants showing a 2.64- and 4.22-fold increase, respectively, compared with WT-LAO. Ultimately, using recombinant LAO in the biotransformation of α-keto acids indicates its great potential as a biocatalyst in industrial production.

FOXO acts as a positive regulator of CncC and deltamethrin tolerance in the red flour beetle, Tribolium castaneum

BACKGROUND

Both forkhead box O (FOXO) and nuclear factor erythroid-derived 2-like-2 (Nrf2) are key transcription factors related to stress responses. Whereas limited studies in mammals and Caenorhabditis elegans have revealed the interaction between FoxO/DAF-16 and Nrf2/SKN-1, the role of FOXO in metabolic detoxification and regulation of the Nrf2-Keap1 signaling pathway are poorly understood in insects.

RESULTS

Using Tribolium castaneum as a model organism, we found that RNA interference-mediated knockdown of FOXO enhanced deltamethrin-induced lethality by affecting the messenger RNA (mRNA) levels of CYP6BQ cluster genes. We further demonstrated that injection of dsFOXO into the beetle larvae decreased expression of CncC and KEAP1 at both the mRNA and protein level. Notably, dual-luciferase and electrophoretic mobility shift assays both confirmed direct regulation of CncC by FOXO, whereas Keap1 was directly regulated by CncC.

CONCLUSION

FOXO can directly regulate the expression of CncC and indirectly regulate the expression of Keap1 through CncC. The data provide insights into the regulatory mechanisms of the Nrf2-Keap1 signaling pathway in insects.

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.

Recombinant Baculovirus-Produced Grass Carp Reovirus Virus-Like Particles as Vaccine Candidate That Provides Protective Immunity against GCRV Genotype II Infection in Grass Carp

Grass carp reovirus (GCRV) leads to severe hemorrhagic disease in grass carp (Ctenopharyngodon idella) and causes economic losses in grass carp aquaculture. Recent epidemiological investigations showed that GCRV genotype II is the dominant subtype in China. Therefore, it is very important to develop a novel vaccine for preventing diseases caused by GCRV genotype II. In this study, we employed a bac-to-bac expression system to generate GCRV-II-based virus-like particles (VLPs). Previous studies have shown that the structural proteins VP3, VP4, and VP38 encoded by the segments S3, S6, and S10 of type II GCRV are immunogenic. Hence, the GCRV-VLPs were produced by co-infection of sf9 cells with recombinant baculoviruses PFBH-VP3, PFBH-VP4, and PFBH-VP38. The expressions of VP3, VP4, and VP38 proteins in GCRV-VLPs were tested by IFA and Western blot analysis. By electron microscopic observations of ultrathin sections, purified VLPs showed that the expressed proteins are similar in shape to GCRV genotype II with a size range from 40 nm to 60 nm. The immunogenicity of GCRV-VLPs was evaluated by the injection immunization of grass carp. The analysis of serum-specific IgM antibody showed that grass carp immunized with GCRV-VLPs produced GCRV-specific antibodies. Furthermore, injection with GCRV-VLPs increased the expressions of immune-related genes (IgM, IFN, TLR3, TLR7) in the spleen and kidney. In addition, grass carp immunized with a GCRV-VLPs-based vaccine showed a relative percent survival rate (RPS) of 83.33% after challenge. The data in this study showed that GCRV-VLPs demonstrated an excellent immunogenicity and represent a promising approach for vaccine development against GCRV genotype II infection.

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.