Aldehyde dehydrogenase diversity in bacteria of the Pseudomonas genus

The aldehyde dehydrogenase superfamilies: correlations and deviations in structure and function

Aldehyde dehydrogenases participate in many biochemical pathways, either by degrading organic substrates via organic acids or by producing reactive aldehyde intermediates in many biosynthetic pathways, and are becoming increasingly important for constructing synthetic metabolic pathways. Although they consist of simple and highly conserved basic structural motifs, they exhibit a surprising variability in the reactions catalyzed. We attempt here to give an overview of the known enzymes of two superfamilies comprising the known aldehyde dehydrogenases, focusing on their structural similarities and the residues involved in the catalytic reactions. The analysis reveals that the enzymes of the two superfamilies share many common traits and probably have a common evolutionary origin. While all enzymes catalyzing irreversible aldehyde oxidation to acids exhibit a universally conserved reaction mechanism with shared catalytic active-site residues, the enzymes capable of reducing activated acids to aldehydes deviate from this mechanism, displaying different active-site modifications required to allow these reactions which apparently evolved independently in different enzyme subfamilies. KEY POINTS: • The two aldehyde dehydrogenase superfamilies share significant similarities. • Catalytic amino acids of irreversibly acting AlDH are universally conserved. • Reductive or reversible reactions are enabled by water exclusion via the loss of conserved residues.

Endogenous ethanol production in health and disease

The gut microbiome exerts metabolic actions on distal tissues and organs outside the intestine, partly through microbial metabolites that diffuse into the circulation. The disruption of gut homeostasis results in changes to microbial metabolites, and more than half of the variance in the plasma metabolome can be explained by the gut microbiome. Ethanol is a major microbial metabolite that is produced in the intestine of nearly all individuals; however, elevated ethanol production is associated with pathological conditions such as metabolic dysfunction-associated steatotic liver disease and auto-brewery syndrome, in which the liver's capacity to metabolize ethanol is surpassed. In this Review, we describe the mechanisms underlying excessive ethanol production in the gut and the role of ethanol catabolism in mediating pathogenic effects of ethanol on the liver and host metabolism. We conclude by discussing approaches to target excessive ethanol production by gut bacteria.

Polyamine-Derived Aminoaldehydes and Acrolein: Cytotoxicity, Reactivity and Analysis of the Induced Protein Modifications

Polyamines participate in the processes of cell growth and development. The degradation branch of their metabolism involves amine oxidases. The oxidation of spermine, spermidine and putrescine releases hydrogen peroxide and the corresponding aminoaldehyde. Polyamine-derived aminoaldehydes have been found to be cytotoxic, and they represent the subject of this review. 3-aminopropanal disrupts the lysosomal membrane and triggers apoptosis or necrosis in the damaged cells. It is implicated in the pathogenesis of cerebral ischemia. Furthermore, 3-aminopropanal yields acrolein through the elimination of ammonia. This reactive aldehyde is also generated by the decomposition of aminoaldehydes produced in the reaction of serum amine oxidase with spermidine or spermine. In addition, acrolein is a common environmental pollutant. It causes covalent modifications of proteins, including carbonylation, the production of Michael-type adducts and cross-linking, and it has been associated with inflammation-related diseases. APAL and acrolein are detoxified by aldehyde dehydrogenases and other mechanisms. High-performance liquid chromatography, immunochemistry and mass spectrometry have been largely used to analyze the presence of polyamine-derived aminoaldehydes and protein modifications elicited by their effect. However, the main and still open challenge is to find clues for discovering clear linkages between aldehyde-induced modifications of specific proteins and the development of various diseases.

Human Aldehyde Dehydrogenases: A Superfamily of Similar Yet Different Proteins Highly Related to Cancer

The superfamily of human aldehyde dehydrogenases (hALDHs) consists of 19 isoenzymes which are critical for several physiological and biosynthetic processes and play a major role in the organism's detoxification via the NAD(P) dependent oxidation of numerous endogenous and exogenous aldehyde substrates to their corresponding carboxylic acids. Over the last decades, ALDHs have been the subject of several studies as it was revealed that their differential expression patterns in various cancer types are associated either with carcinogenesis or promotion of cell survival. Here, we attempt to provide a thorough review of hALDHs' diverse functions and 3D structures with particular emphasis on their role in cancer pathology and resistance to chemotherapy. We are especially interested in findings regarding the association of structural features and their changes with effects on enzymes' functionalities. Moreover, we provide an updated outline of the hALDHs inhibitors utilized in experimental or clinical settings for cancer therapy. Overall, this review aims to provide a better understanding of the impact of ALDHs in cancer pathology and therapy from a structural perspective.

Isolation, purification, and mass spectrometry identification of the enzyme involved in citrus flavor (+)-valencene biotransformation to (+)-nootkatone by Yarrowia lipolytica

BACKGROUND

(+)-Nootkatone is a highly valuable sesquiterpene compound that can be used as an aromatic in the food industry because of its grapefruit flavor and low sensory threshold. The unconventional yeast Yarrowia lipolytica has many unique physical and chemical properties, metabolic characteristics, and genetic structure, which has aroused the interest of researchers. Previous research showed that Y. lipolytica possesses the ability to transform the sesquiterpene (+)-valencene to (+)-nootkatone. The aim of this study was to isolate, purify, and identify the enzyme involved in the (+)-valencene bioconversion to (+)-nootkatone by Y. lipolytica.

RESULTS

In this study, ultrasonic-assisted extraction, ammonium sulfate precipitation, anion-exchange chromatography, and gel-filtration chromatography were used to separate and purify the enzyme involved in the (+)-valencene bioconversion by Y. lipolytica. The protein was identified as aldehyde dehydrogenase (ALDH) (gene0658) using sodium dodecyl sulfate polyacrylamide gel electrophoresis and liquid chromatography-tandem mass spectrometry analysis. The ALDH had the highest activity when the pH value was 6.0 and the temperature was 30 °C. The activity of ALDH was significantly stimulated by ferrous ions and inhibited by barium, calcium, and magnesium ions.

CONCLUSION

This is the first time that ALDH was found to participate in (+)-valencene biotransformation by Y. lipolytica. It may be involved in regulating the microbial transformation of (+)-valencene to (+)-nootkatone through redox characteristics. This study provides a theoretical basis and reference for the biological synthesis of citrus flavor (+)-nootkatone. © 2023 Society of Chemical Industry.

Complementary Biotransformation of Antimicrobial Triclocarban Obviously Mitigates Nitrous Oxide Emission toward Sustainable Microbial Denitrification

Sustainable nitrogen cycle is an essential biogeochemical process that ensures ecosystem safety and byproduct greenhouse gas nitrous oxide reduction. Antimicrobials are always co-occurring with anthropogenic reactive nitrogen sources. However, their impacts on the ecological safety of microbial nitrogen cycle remain poorly understood. Here, a denitrifying bacterial strain Paracoccus denitrificans PD1222 was exposed to a widespread broad-spectrum antimicrobial triclocarban (TCC) at environmental concentrations. The denitrification was hindered by TCC at 25 μg L^-1 and was completely inhibited once the TCC concentration exceeded 50 μg L^-1. Importantly, the accumulation of N₂O at 25 μg L^-1 of TCC was 813 times as much as the control group without TCC, which attributed to the significantly downregulated expression of nitrous oxide reductase and the genes related to electron transfer, iron, and sulfur metabolism under TCC stress. Interestingly, combining TCC-degrading denitrifying Ochrobactrum sp. TCC-2 with strain PD1222 promoted the denitrification process and mitigated N₂O emission by 2 orders of magnitude. We further consolidated the importance of complementary detoxification by introducing a TCC-hydrolyzing amidase gene tccA from strain TCC-2 into strain PD1222, which successfully protected strain PD1222 against the TCC stress. This study highlights an important link between TCC detoxification and sustainable denitrification and suggests a necessity to assess the ecological risks of antimicrobials in the context of climate change and ecosystem safety.

The uncharacterized Pseudomonas aeruginosa PA4189 is a novel and efficient aminoacetaldehyde dehydrogenase

Neither the Pseudomonas aeruginosa aldehyde dehydrogenase encoded by the PA4189 gene nor its ortholog proteins have been biochemically or structurally characterized and their physiological function is unknown. We cloned the PA4189 gene, obtained the PA4189 recombinant protein, and studied its structure-function relationships. PA4189 is an NAD+-dependent aminoaldehyde dehydrogenase highly efficient with protonated aminoacetaldehyde and 3-aminopropionaldehyde, which are much more preferred to the non-protonated species as indicated by pH studies. Based on the higher activity with aminoacetaldehyde than with 3-aminopropionaldehyde, we propose that aminoacetaldehyde might be the PA4189 physiological substrate. Even though at the physiological pH of P. aeruginosa cells the non-protonated aminoacetaldehyde species will be predominant, and despite the competition of these species with the protonated ones, PA4189 would very efficiently oxidize ACTAL in vivo, producing glycine. To our knowledge, PA4189 is the first reported enzyme that might metabolize ACTAL, which is considered a dead-end metabolite because its consuming reactions are unknown. The PA4189 crystal structure reported here suggested that the charge and size of the active-site residue Glu457, which narrows the aldehyde-entrance tunnel, greatly define the specificity for small positively charged aldehydes, as confirmed by the kinetics of the E457G and E457Q variants. Glu457 and the residues that determine Glu457 conformation inside the active site are conserved in the PA4189 orthologs, which we only found in proteobacteria species. Also is conserved the PA4189 genomic neighborhood, which suggests that PA4189 participates in an uncharacterized metabolic pathway. Our results open the door to future efforts to characterize this pathway.

Evolution, family expansion, and functional diversification of plant aldehyde dehydrogenases

Aldehyde dehydrogenases (ALDHs) act as "aldehyde scavengers" in plants, eliminating reactive aldehydes and hence performing a crucial part in response to stress. ALDH has been specified multiple activities since its identification in the mammalian system 72 years ago. But the most widely researched role in plants is their engagement in stress tolerance. Multiple ALDH families are found in both animals and plants, and many genes are substantially conserved within these two evolutionary diverse taxa, yet both have their unique members/families. A total of twenty-four ALDH protein family has been reported across organisms, where plants contain fourteen families. Surprisingly, the number of genes in the ALDH superfamily has risen in the higher plants because of genome duplication and expansion, indicating the functional versatilely. Observed expansion in the ALDH isoforms might provide high plasticity in their actions to achieve diversified roles in the plant. The physiological importance and functional diversity of ALDHs including plant development and environmental stress adaptability, and their evolution in plants has been studied extensively. Future investigations need to focus on evaluating the individual and interconnecting function of multiple ALDH isoforms across organisms in providing plants with proper development, maturation, and adaptability against harsh environmental conditions.

The StkSR Two-Component System Influences Colistin Resistance in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic human pathogen responsible for numerous severe nosocomial infections. Genome analysis on the A. baumannii clinical isolate 04117201 revealed the presence of 13 two-component signal transduction systems (TCS). Of these, we examined the putative TCS named here as StkSR. The stkR response regulator was deleted via homologous recombination and its progeny, ΔstkR, was phenotypically characterized. Antibiogram analyses of ΔstkR cells revealed a two-fold increase in resistance to the clinically relevant polymyxins, colistin and polymyxin B, compared to wildtype. PAGE-separation of silver stained purified lipooligosaccharide isolated from ΔstkR and wildtype cells ruled out the complete loss of lipooligosaccharide as the mechanism of colistin resistance identified for ΔstkR. Hydrophobicity analysis identified a phenotypical change of the bacterial cells when exposed to colistin. Transcriptional profiling revealed a significant up-regulation of the pmrCAB operon in ΔstkR compared to the parent, associating these two TCS and colistin resistance. These results reveal that there are multiple levels of regulation affecting colistin resistance; the suggested ‘cross-talk’ between the StkSR and PmrAB two-component systems highlights the complexity of these systems.

Probe-based qPCR assay enables the rapid and specific detection of bacterial degrading genes for the pesticide metaldehyde in soil

Metaldehyde, a molluscicide pesticide, has been identified as a pollutant of concern due to its repeated detection in drinking water, thereby generating numerous compliance failures for water utilities. Biological degradation potential for metaldehyde is widespread in soils, occurring at different rates, but to date, no molecular methods for its assessment have been reported. Here, three genes belonging to a shared metaldehyde-degrading gene cluster present in bacteria were used as candidates for development of a quantitative PCR (qPCR) assay for assessing the metaldehyde-degrading potential in soil. Screening of gene targets, primer pairs and optimization of reaction conditions led to the development of a sensitive and specific probe-based qPCR method for quantifying the mahY metaldehyde-degrading gene from soil. The technique was tested across 8 soils with different compositions and origins. The degrading pathway was detected in 4/8 soils, in which a higher number of gene copies correlated with periods of greater metaldehyde removal. Additionally, swift elimination of the pesticide was observed in soils with an elevated initial number of mahY gene copies. The gene cluster was not detected in other soils, even though metaldehyde removal occurred, indicating that other biological degrading pathways are also important in nature. The method described here is the first one available to estimate the microbial metaldehyde degradation potential and activity in soils, and can also be used to detect degrading microorganisms in systems such as sand filters for water purification or to monitor degrading strains in engineered processes.

Extracellular degradation of a polyurethane oligomer involving outer membrane vesicles and further insights on the degradation of 2,4-diaminotoluene in Pseudomonas capeferrum TDA1

The continuing reports of plastic pollution in various ecosystems highlight the threat posed by the ever-increasing consumption of synthetic polymers. Therefore, Pseudomonas capeferrum TDA1, a strain recently isolated from a plastic dump site, was examined further regarding its ability to degrade polyurethane (PU) compounds. The previously reported degradation pathway for 2,4-toluene diamine, a precursor and degradation intermediate of PU, could be confirmed by RNA-seq in this organism. In addition, different cell fractions of cells grown on a PU oligomer were tested for extracellular hydrolytic activity using a standard assay. Strikingly, purified outer membrane vesicles (OMV) of P. capeferrum TDA1 grown on a PU oligomer showed higher esterase activity than cell pellets. Hydrolases in the OMV fraction possibly involved in extracellular PU degradation were identified by mass spectrometry. On this basis, we propose a model for extracellular degradation of polyester-based PUs by P. capeferrum TDA1 involving the role of OMVs in synthetic polymer degradation.

Study of ALDH from Thermus thermophilus-Expression, Purification and Characterisation of the Non-Substrate Specific, Thermophilic Enzyme Displaying Both Dehydrogenase and Esterase Activity

Aldehyde dehydrogenases (ALDH), found in all kingdoms of life, form a superfamily of enzymes that primarily catalyse the oxidation of aldehydes to form carboxylic acid products, while utilising the cofactor NAD(P)⁺. Some superfamily members can also act as esterases using p-nitrophenyl esters as substrates. The ALDH_Tt from Thermus thermophilus was recombinantly expressed in E. coli and purified to obtain high yields (approximately 15–20 mg/L) and purity utilising an efficient heat treatment step coupled with IMAC and gel filtration chromatography. The use of the heat treatment step proved critical, in its absence decreased yield of 40% was observed. Characterisation of the thermophilic ALDH_Tt led to optimum enzymatic working conditions of 50 °C, and a pH of 8. ALDH_Tt possesses dual enzymatic activity, with the ability to act as a dehydrogenase and an esterase. ALDH_Tt possesses broad substrate specificity, displaying activity for a range of aldehydes, most notably hexanal and the synthetic dialdehyde, terephthalaldehyde. Interestingly, para-substituted benzaldehydes could be processed efficiently, but ortho-substitution resulted in no catalytic activity. Similarly, ALDH_Tt displayed activity for two different esterase substrates, p-nitrophenyl acetate and p-nitrophenyl butyrate, but with activities of 22.9% and 8.9%, respectively, compared to the activity towards hexanal.

The tetrameric assembly of 2-aminomuconic 6-semialdehyde dehydrogenase is a functional requirement of cofactor NAD+ binding

The bacterium Pseudomonas sp. AP-3 is able to use the environmental pollutant 2-aminophenol as its sole source of carbon, nitrogen, and energy. Eight genes (amnA, B, C, D, E, F, G, and H) encoding 2-aminophenol metabolizing enzymes are clustered into a single operon. 2-Aminomuconic 6-semialdehyde dehydrogenase (AmnC), a member of the aldehyde dehydrogenase (ALDH) superfamily, is responsible for oxidizing 2-aminomuconic 6-semialdehyde to 2-aminomuconate. In contrast to many other members of the ALDH superfamily, the structural basis of the catalytic activity of AmnC remains elusive. Here, we present the crystal structure of AmnC, which displays a homotetrameric quaternary assembly that is directly involved in its enzymatic activity. The tetrameric state of AmnC in solution was also presented using small-angle X-ray scattering. The tetramerization of AmnC is mediated by the assembly of a protruding hydrophobic beta-strand motif and residues V121 and S123 located in the NAD⁺ -binding domain of each subunit. Dimeric mutants of AmnC dramatically lose NAD⁺ binding affinity and failed to oxidize the substrate analogue 2-hydroxymuconate-6-semialdehyde to α-hydroxymuconic acid, indicating that tetrameric assembly of AmnC is functional requirement.

The critical role of the aldehyde dehydrogenase PauC in spermine, spermidine, and diaminopropane toxicity in Pseudomonas aeruginosa: Its possible use as a drug target

The opportunistic human pathogen Pseudomonas aeruginosa exhibits great resistance to antibiotics; so, new therapeutic agents are urgently needed. Since polyamines levels are incremented in infected tissues, we explored whether the formation of a toxic aldehyde in polyamines degradation can be exploited in combating infection. We cloned the gene encoding the only aminoaldehyde dehydrogenase involved in P. aeruginosa polyamines-degradation routes, PaPauC, overexpressed this enzyme, and found that it oxidizes 3-aminopropionaldehyde (APAL) and 3-glutamyl-3-aminopropionaldehyde (GluAPAL) - produced in spermine (Spm), spermidine (Spd), and diaminopropane (Dap) degradation, as well as 4-aminobutyraldehyde (ABAL) and 4-glutamyl-4-aminobutyraldehyde (GluABAL) - formed in putrescine (Put) degradation. As the catalytic efficiency of PaPauC with APAL was 30-times lower than with GluAPAL, and GluAPAL is predominantly formed, APAL will be poorly oxidized 'in vivo'. We found polyamines-induced increases in the PaPauC activity of cell crude-extracts and in the expression of the PapauC gene that were diminished by glucose. Spm, Spd, or Dap, but not Put, were toxic to P. aeruginosa even in the presence of other carbon and nitrogen sources, particularly to a strain with the PapauC gene disrupted. APAL, but not GluAPAL, was highly toxic even to wild-type cells, suggesting that its accumulation, particularly in the absence of, or low, PaPauC activity is responsible for the toxicity of Spm, Spd, and Dap. Our results shed light on the toxicity mechanism of these three polyamines and strongly support the critical role of PaPauC in this toxicity. Thus, PaPauC emerges as a novel potential drug target whose inhibition might help in combating infection by this important pathogen.

Different Non-cage Housing Systems Alter Duodenal and Cecal Microbiota Composition in Shendan Chickens

Housing systems are among the most important non-genetic factors affecting hen production performance and intestinal microbes. With increased interest in animal welfare, cage-free laying hen housing systems have become common, providing behavioral freedom and health benefits. The present study aimed to compare the effects of plastic net housing system (NRS) and floor litter housing system (LRS) on the composition and function of the duodenal and cecal microbiota in Shendan chicken, one of the most popular laying hen strains in China. The associations between the differential microbiota abundance and production traits and intestinal morphological parameters were determined. Compared with the LRS, the NRS improved the laying rate (p < 0.05) and increased the villus height (VH) of the duodenum (p < 0.05) and the VH-to-crypt depth ratio (VCR) of the cecum (p < 0.05). Alpha diversity analysis showed that LRS chickens had a significantly higher diversity and richness than NRS chickens. Beta diversity analysis demonstrated differences in the microbiota composition based on housing systems. Within the cecum, Proteobacteria and Kiritimatiellaeota were significantly more abundant in the LRS than in the NRS (p < 0.05), while Bacteroidetes were significantly less abundant in the LRS (p < 0.05). Phascolarctobacterium and Ruminococcaceae_UCG-005 were significantly less abundant in the LRS (p < 0.05) compare to the NRS. Within the duodenum, Lactobacillus was significantly less abundant in the LRS (p < 0.05) than in the NRS, while Pseudomonas was significantly more abundant in the LRS (p < 0.05). Cecal Phascolarctobacterium and Ruminococcaceae_UCG-005 were significantly positively correlated with eggshell strength (R = 0.608, p < 0.01) and egg weight (R = 0.526, p < 0.05), respectively. Duodenal Lactobacillus was significantly positively correlated with VH and VCR (R = 0.548 and 0.565, p < 0.05), while Pseudomonas was significantly negatively correlated with the Haugh unit (R = -0.550, p < 0.05). In conclusion, there are differences in the cecal and duodenal microbiota compositions of Shendan laying hens reared in different non-cage housing systems, and the NRS was superior to the LRS in improving the laying performance and intestinal morphology and microecological environment.

Double agent indole-3-acetic acid (IAA): Mechanistic analysis of indole-3-acetaldehyde dehydrogenase AldA that synthesizes IAA, an auxin that aids bacterial virulence

The large diversity of organisms inhabiting various environmental niches on our planet are engaged in a lively exchange of biomolecules, including nutrients, hormones, and vitamins. In a quest to survive, organisms that we define as pathogens employ innovative methods to extract valuable resources from their host leading to an infection. One such instance is where plant-associated bacterial pathogens synthesize and deploy hormones or their molecular mimics to manipulate the physiology of the host plant. This commentary describes one such specific example—the mechanism of the enzyme AldA, an aldehyde dehydrogenase (ALDH) from the bacterial plant pathogen Pseudomonas syringae which produces the plant auxin hormone indole-3-acetic acid (IAA) by oxidizing the substrate indole-3-acetaldehyde (IAAld) using the cofactor nicotinamide adenine dinucleotide (NAD⁺) (Bioscience Reports (2020) 40(12), https://doi.org/10.1042/BSR20202959). Using mutagenesis, enzyme kinetics, and structural analysis, Zhang et al. established that the progress of the reaction hinges on the formation of two distinct conformations of NAD(H) during the reaction course. Additionally, a key mutation in the AldA active site ‘aromatic box’ changes the enzyme’s preference for an aromatic substrate to an aliphatic one. Our commentary concludes that such molecular level investigations help to establish the nature of the dynamics of NAD(H) in ALDH-catalyzed reactions, and further show that the key active site residues control substrate specificity. We also contemplate that insights from the present study can be used to engineer novel ALDH enzymes for environmental, health, and industrial applications.

Heterotrophic enzymatic biotransformations of organic micropollutants in activated sludge

While heterotrophic microorganisms constitute the major fraction of activated sludge biomass, the role of heterotrophs in the biotransformation of organic micropollutants (OMPs) has not been fully elucidated. Yet, such knowledge is essential, particularly when conceiving novel wastewater treatment plants based on a two-stage process including an A-stage under heterotrophic conditions and a B-stage based on anammox activity. Biotransformation of OMPs in activated sludge is thought to mostly occur cometabolically thanks to the action of low specificity enzymes involved in the metabolism of the primary substrates. For a better understanding of the process, it is important to determine such enzymatic activities and the underlying mechanisms involved in OMPs biotransformation. This task has proven to be difficult due to the lack of information about the enzymatic processes and the complexity of the biological systems present in activated sludge. In this paper, a continuous aerobic heterotrophic reactor following 20 OMPs at environmental concentrations was operated to (i) assess the potential of heterotrophs during the cometabolic biotransformation of OMPs, (ii) identify biotransformation reactions catalyzed by aerobic heterotrophs and (iii) predict possible heterotrophic enzymatic activities responsible for such biotransformations. Contradicting previous reports on the dominant role of nitrifiers in OMPs removal during activated sludge treatment, the heterotrophic population proved its capacity to biotransform the OMPs to extents equivalent to reported values in nitrifying activated sludge plants. Besides, 12 transformation products potentially formed through the activity of several enzymes present in heterotrophs, including monooxygenases, dioxygenases, hydrolases and transferases, were identified.

Sensitivity enhancement of the SPR biosensor for Pseudomonas bacterial detection employing a silicon-barium titanate structure

A novel, to the best of our knowledge, surface plasmon resonance (SPR) sensor, employing a silicon-barium titanate structure for Pseudomonas bacterial detection, is designed. Three bacterial attachments operate as a protective layer for the detection process with refractive indices (RI) of 1.437, 1.49368, and 1.5265. Performance analysis shows a sensitivity (S) of 155, 168, and 370°/RIU at RI of 1.5265 for Structures 1, 2, and 3, respectively. Additionally, the proposed sensor (Structure 3) accomplishes a magnified figure of merit (FOM) of 86.43 and quality factor of 86.65 at the RI of 1.5265. Finally, the proposed sensor's performance is compared with that of the existing sensors, thus demonstrating a heightened S and FOM.

Insights into Aldehyde Dehydrogenase Enzymes: A Structural Perspective

Aldehyde dehydrogenases engage in many cellular functions, however their dysfunction resulting in accumulation of their substrates can be cytotoxic. ALDHs are responsible for the NAD(P)-dependent oxidation of aldehydes to carboxylic acids, participating in detoxification, biosynthesis, antioxidant and regulatory functions. Severe diseases, including alcohol intolerance, cancer, cardiovascular and neurological diseases, were linked to dysfunctional ALDH enzymes, relating back to key enzyme structure. An in-depth understanding of the ALDH structure-function relationship and mechanism of action is key to the understanding of associated diseases. Principal structural features 1) cofactor binding domain, 2) active site and 3) oligomerization mechanism proved critical in maintaining ALDH normal activity. Emerging research based on the combination of structural, functional and biophysical studies of bacterial and eukaryotic ALDHs contributed to the appreciation of diversity within the superfamily. Herewith, we discuss these studies and provide our interpretation for a global understanding of ALDH structure and its purpose–including correct function and role in disease. Our analysis provides a synopsis of a common structure-function relationship to bridge the gap between the highly studied human ALDHs and lesser so prokaryotic models.

Investigating the reaction and substrate preference of indole-3-acetaldehyde dehydrogenase from the plant pathogen Pseudomonas syringae PtoDC3000

Aldehyde dehydrogenases (ALDHs) catalyze the conversion of various aliphatic and aromatic aldehydes into corresponding carboxylic acids. Traditionally considered as housekeeping enzymes, new biochemical roles are being identified for members of ALDH family. Recent work showed that AldA from the plant pathogen Pseudomonas syringae strain PtoDC3000 (PtoDC3000) functions as an indole-3-acetaldehyde dehydrogenase for the synthesis of indole-3-acetic acid (IAA). IAA produced by AldA allows the pathogen to suppress salicylic acid-mediated defenses in the model plant Arabidopsis thaliana. Here we present a biochemical and structural analysis of the AldA indole-3-acetaldehyde dehydrogenase from PtoDC3000. Site-directed mutants targeting the catalytic residues Cys302 and Glu267 resulted in a loss of enzymatic activity. The X-ray crystal structure of the catalytically inactive AldA C302A mutant in complex with IAA and NAD+ showed the cofactor adopting a conformation that differs from the previously reported structure of AldA. These structures suggest that NAD+ undergoes a conformational change during the AldA reaction mechanism similar to that reported for human ALDH. Site-directed mutagenesis of the IAA binding site indicates that changes in the active site surface reduces AldA activity; however, substitution of Phe169 with a tryptophan altered the substrate selectivity of the mutant to prefer octanal. The present study highlights the inherent biochemical versatility of members of the ALDH enzyme superfamily in P. syringae.

Novel insights into host-pathogen interactions of large yellow croakers ( Larimichthys crocea) and pathogenic bacterium Pseudomonas plecoglossicida using time-resolved dual RNA-seq of infected spleens

Host-pathogen interactions are highly complex, involving large dynamic changes in gene expression during infection. These interactions are fundamental to understanding anti-infection immunity of hosts, as well as the pathogenesis of pathogens. For bacterial pathogens interacting with animal hosts, time-resolved dual RNA-seq of infected tissue is difficult to perform due to low pathogen load in infected tissue. In this study, an acute infection model of Larimichthys crocea infected by Pseudomonas plecoglossicida was established. The spleens of infected fish exhibited typical symptoms, with a maximum bacterial load at two days post-injection (dpi). Time-resolved dual RNA-seq of infected spleens was successfully applied to study host-pathogen interactions between L. crocea and P. plecoglossicida. The spleens of infected L. crocea were subjected to dual RNA-seq, and transcriptome data were compared with those of noninfected spleens or in vitro cultured bacteria. Results showed that pathogen-host interactions were highly dynamically regulated, with corresponding fluctuations in host and pathogen transcriptomes during infection. The expression levels of many immunogenes involved in cytokine-cytokine receptor, Toll-like receptor signaling, and other immune-related pathways were significantly up-regulated during the infection period. Furthermore, metabolic processes and the use of oxygen in L. crocea were strongly affected by P. plecoglossicida infection. The WGCNA results showed that the metabolic process was strongly related to the entire immune process. For P. plecoglossicida, the expression levels of motility-related genes and flagellum assembly-related genes were significantly up-regulated. The results of this study may help to elucidate the interactions between L. crocea and P. plecoglossicida.

The plant pathogen enzyme AldC is a long-chain aliphatic aldehyde dehydrogenase

Aldehyde dehydrogenases are versatile enzymes that serve a range of biochemical functions. Although traditionally considered metabolic housekeeping enzymes because of their ability to detoxify reactive aldehydes, like those generated from lipid peroxidation damage, the contributions of these enzymes to other biological processes are widespread. For example, the plant pathogen Pseudomonas syringae strain PtoDC3000 uses an indole-3-acetaldehyde dehydrogenase to synthesize the phytohormone indole-3-acetic acid to elude host responses. Here we investigate the biochemical function of AldC from PtoDC3000. Analysis of the substrate profile of AldC suggests that this enzyme functions as a long-chain aliphatic aldehyde dehydrogenase. The 2.5 Å resolution X-ray crystal of the AldC C291A mutant in a dead-end complex with octanal and NAD⁺ reveals an apolar binding site primed for aliphatic aldehyde substrate recognition. Functional characterization of site-directed mutants targeting the substrate- and NAD(H)-binding sites identifies key residues in the active site for ligand interactions, including those in the "aromatic box" that define the aldehyde-binding site. Overall, this study provides molecular insight for understanding the evolution of the prokaryotic aldehyde dehydrogenase superfamily and their diversity of function.