Identification, cloning, and expression of L-amino acid oxidase from marine Pseudoalteromonas sp. B3

The Pseudoalteromonas luteoviolacea L-amino Acid Oxidase with Antimicrobial Activity Is a Flavoenzyme

The marine environment is a rich source of antimicrobial compounds with promising pharmaceutical and biotechnological applications. The Pseudoalteromonas genus harbors one of the highest proportions of bacterial species producing antimicrobial molecules. For decades, the presence of proteins with L-amino acid oxidase (LAAO) and antimicrobial activity in Pseudoalteromonas luteoviolacea has been known. Here, we present for the first time the identification, cloning, characterization and phylogenetic analysis of Pl-LAAO, the enzyme responsible for both LAAO and antimicrobial activity in P. luteoviolacea strain CPMOR-2. Pl-LAAO is a flavoprotein of a broad substrate range, in which the hydrogen peroxide generated in the LAAO reaction is responsible for the antimicrobial activity. So far, no protein with a sequence similarity to Pl-LAAO has been cloned or characterized, with this being the first report on a flavin adenine dinucleotide (FAD)-containing LAAO with antimicrobial activity from a marine microorganism. Our results revealed that 20.4% of the sequenced Pseudoalteromonas strains (specifically, 66.6% of P. luteoviolacea strains) contain Pl-laao similar genes, which constitutes a well-defined phylogenetic group. In summary, this work provides insights into the biological significance of antimicrobial LAAOs in the Pseudoalteromonas genus and shows an effective approach for the detection of novel LAAOs, whose study may be useful for biotechnological applications.

Amplification and bioinformatics analysis of conserved FAD-binding region of L-amino acid oxidase (LAAO) genes in gastropods compared to other organisms

This study aimed to investigate the conserved FAD-binding region of the L-amino acid oxidase (LAAO) genes in twelve gastropod genera commonly found in Thailand compared to those in other organisms using molecular cloning, nucleotide sequencing and bioinformatics analysis. Genomic DNA of gastropods and other invertebrates was extracted and screened using primers specific to the conserved FAD-binding region of LAAO. The amplified 143-bp fragments were cloned and sequenced. The obtained nucleotide sequences of 21 samples were aligned and phylogenetically compared to the LAAO-conserved FAD-binding regions of 210 other organisms from the NCBI database. Translated amino acid sequences of these samples were used in phylogenetics and pattern analyses. The phylogenetic trees showed clear separation of the conserved regions in fungi, invertebrates, and vertebrates. Alignment of the conserved 47-amino-acid FAD-binding region of the LAAOs showed 150 unique sequences among the 231 samples and these patterns were different from those of other flavoproteins in the amine oxidase family. An amino acid pattern analysis of five sub-regions (bFAD, FAD, FAD-GG, GG, and aGG) within the FAD-binding sequence showed high variation at the FAD-GG sub-region. Pattern analysis of secondary structures indicated the aGG sub-region as having the highest structural variation. Cluster analysis of these patterns revealed two major clusters representing the mollusc clade and the vertebrate clade. Thus, molecular phylogenetics and pattern analyses of sequence and structural variations could reflect evolutionary relatedness and possible structural conservation to maintain specific function within the FAD-binding region of the LAAOs in gastropods compared to other organisms.

Reactive oxygen species-scavenging system is involved in l-amino acid oxidase accumulation in Pseudoalteromonas sp. B3

To date, the mechanisms underlying the flavoprotein l-amino acid oxidase (LAAO) accumulation in cells remain unclear. In this study, using LAAO-producer Pseudoalteromonas spp. as model organisms, we found that the cell biomass is negatively associated with LAAO accumulation, whereas the LAAO accumulation is positively associated with the reactive oxygen species (ROS)-scavenging capability. The expression levels of ROS-scavenging-associated genes were up-regulated with LAAO accumulation in Pseudoalteromonas cells, which is presumably due to the requirement for the removal of LAAO-induced ROS. Exogenous H₂O₂ exposure experiment supported that the ROS-scavenging system is associated with LAAO accumulation in Pseudoalteromonas. All these observations indicate that ROS-scavenging capacity determines LAAO accumulation in bacterial cells. Our results shed a light on understanding the mechanism underlying controlling and adapting to LAAO accumulation in Pseudoalteromonas. Besides, our findings are critical to the improvement of heterologous expression of active LAAO in the future.

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.

Exploring regulation genes involved in the expression of L-amino acid oxidase in Pseudoalteromonas sp. Rf-1

Bacterial L-amino acid oxidase (LAAO) is believed to play important biological and ecological roles in marine niches, thus attracting increasing attention to understand the regulation mechanisms underlying its production. In this study, we investigated genes involved in LAAO production in marine bacterium Pseudoalteromonas sp. Rf-1 using transposon mutagenesis. Of more than 4,000 mutants screened, 15 mutants showed significant changes in LAAO activity. Desired transposon insertion was confirmed in 12 mutants, in which disrupted genes and corresponding functionswere identified. Analysis of LAAO activity and lao gene expression revealed that GntR family transcriptional regulator, methylase, non-ribosomal peptide synthetase, TonB-dependent heme-receptor family, Na⁺/H⁺ antiporter and related arsenite permease, N-acetyltransferase GCN5, Ketol-acid reductoisomerase and SAM-dependent methytransferase, and their coding genes may be involved in either upregulation or downregulation pathway at transcriptional, posttranscriptional, translational and/or posttranslational level. The nhaD and sdmT genes were separately complemented into the corresponding mutants with abolished LAAO-activity. The complementation of either gene can restore LAAO activity and lao gene expression, demonstrating their regulatory role in LAAO biosynthesis. This study provides, for the first time, insights into the molecular mechanisms regulating LAAO production in Pseudoalteromonas sp. Rf-1, which is important to better understand biological and ecological roles of LAAO.