FabG: from a core to circumstantial catalyst

Diversity and functional features of the root-associated bacteriome are dependent on grapevine susceptibility to Plasmopara viticola

BACKGROUND

Plant health depends on beneficial interactions between the roots and their microbiomes. Despite recent progress on the role of the grapevine microbiome, the taxonomic identity and functional traits of microbial taxa specific to healthy or Plasmopara viticola-diseased plants, as well as to the susceptible or resistant cultivar are unknown. Using metabarcoding and shotgun metagenomics sequencing, we investigated the effect of downy mildew on the root-associated microbiome (rhizospheric soil, rhizoplane and endosphere) of 41B-grafted susceptible cultivar (Chardonnay) and resistant interspecific hybrid (Voltis) at flowering and veraison stages. The impact of conventional treatment on the rhizomicrobiome assembly of Chardonnay was also evaluated.

RESULTS

Analyses revealed a core bacteriome shared between both susceptible and resistant cultivars. This also highlighted common functional traits between the rhizosphere and rhizoplane bacteriomes in both cultivars. A dysbiosis state was also evidenced by a loss of beneficial communities in the rhizosphere of the P. viticola-infected cultivar. Microbial genome assemblies showed functional differences between healthy and diseased plants, with a loss of Pseudomonas and Phyllobacterium taxa at veraison. This state was mainly characterized by a loss of genes involved in polyamine transport and metabolism in the susceptible cultivar. It was also marked by an increase in population evenness and total bacterial diversity, and the presence of pathogenic species in susceptible plants.

CONCLUSIONS

This study reveals distinct and overlapping bacterial communities and functional genes in the rhizospheric soil, rhizoplane and root endosphere of both susceptible and resistant grapevine cultivars to downy mildew. Microbial diversity and abundant taxa of grapevine roots are influenced by downy mildew and cultivar susceptibility. Common bacterial functions are shared among rhizocompartments of susceptible and resistant cultivars, revealing a dysbiosis state and functional signatures related to plant immunity, especially in the infected-susceptible plants.

Identification and Application of Novel Patulin-Degrading Enzymes from Bacillus subtilis 168

Patulin (PAT), a toxic secondary metabolite produced mainly by Penicillium species that frequently contaminates fruit and fruit-derived products, poses serious health risks to humans and animals. In the present study, three short-chain dehydrogenases/reductases (SDRs) with PAT-degrading ability, designated BsSDR1, BsSDR2, and BsSDR3, were identified from the genome of Bacillus subtilis 168. BsSDR1 and BsSDR2 showed powerful PAT elimination abilities, which can completely convert PAT to nontoxic E-ascladiol. Moreover, BsSDR1, BsSDR2, and BsSDR3 shared the highest sequence identity of 36.03% with the reported PAT-degrading enzymes, indicating that they are novel PAT-degrading enzymes. BsSDR1, BsSDR2, and BsSDR3 exhibited the highest activity against PAT at 40, 40, and 35 °C, respectively. Additionally, BsSDR1, BsSDR2, and BsSDR3 displayed remarkable thermostability, retaining 32.50, 24.63, and 46.74% residual activity, respectively, after incubation at 50 °C for 1 h. Three-dimensional (3D) simulation and site-directed mutagenesis indicated that the catalytic triad formed by the residues (Ser, Tyr, and Lys) was the key for SDR activity, and this conserved catalytic mechanism was followed in the catalytic process of novel PAT-degrading enzymes BsSDR1, BsSDR2, and BsSDR3. More importantly, BsSDR1, BsSDR2, and BsSDR3 can degrade PAT in apple juice at rates of 86.90, 90.17, and 61.57%, respectively. The identification of BsSDR1, BsSDR2, and BsSDR3 enriched the PAT-degrading enzyme libraries, providing promising candidates for PAT decontamination in the food industry.

Transcriptomics-guided optimization of vitamins to enhance erythromycin yield in saccharopolyspora erythraea

Comparative transcriptomics uncovered distinct expression patterns of genes associated with cofactor and vitamin metabolism in the high-yielding mutant strain Saccharopolyspora erythraea HL3168 E3, as compared to the wild-type NRRL 2338. An in-depth analysis was conducted on the effects of nine vitamins, and it was determined that thiamine pyrophosphate (TPP), vitamin B2, vitamin B6, vitamin B9, vitamin B12, and hemin are key enhancers in erythromycin production in E3, increasing the erythromycin titer by 7.96-12.66%. Then, the Plackett-Burman design and the path of steepest ascent were applied to further optimize the vitamin combination for maximum production efficiency, enhancing the erythromycin titer in shake flasks by 39.2%. Otherwise, targeted metabolomics and metabolic flux analysis illuminated how vitamin supplementation modulates the central carbon metabolism with notable effects on the TCA cycle and methionine synthesis to augment the provision of energy and precursors essential for erythromycin synthesis. This work highlights the capacity for precise vitamin supplementation to refine metabolic pathways, thereby boosting erythromycin production, and provides valuable directions for application on an industrial scale.

Structure features of Streptococcus pneumoniae FabG and virtual screening of allosteric inhibitors

Streptococcus pneumoniae, a gram-positive bacterium, is responsible for diverse infections globally, and its antibiotic resistance presents significant challenges to medical advancements. It is imperative to employ various strategies to identify antibiotics. 3-oxoacyl-[acyl-carrier-protein] reductase (FabG) is a key component in the type II fatty acid synthase (FAS II) system, which is a developing target for new anti-streptococcal drugs. We first demonstrated the function of SpFabG in vivo and in vitro and the 2 Å SpFabG structure was elucidated using X-ray diffraction technique. It was observed that the NADPH binding promotes the transformation from tetramers to dimers in solution, suggesting dimers but not tetramer may be the active conformation. By comparing the structures of FabG homologues, we have identified the conserved tetramerization site and further confirmed the mechanism that the tetramerization site mutation leads to a loss of function and destabilization through mutagenesis experiments. Starting from 533,600 compounds, we proceeded with a sequential workflow involving pharmacophore-based virtual screening, molecular docking, and binding energy calculations. Combining all the structural analysis, we identified L1, L2 and L5 as a promising candidate for SpFabG inhibitor, based on the most stable binding mode in comparison to other evaluated inhibitors.

Integrated Metabolomic and Transcriptomic Analysis Reveals the Underlying Antibacterial Mechanisms of the Phytonutrient Quercetin-Induced Fatty Acids Alteration in Staphylococcus aureus ATCC 27217

The utilization of natural products in food preservation represents a promising strategy for the dual benefits of controlling foodborne pathogens and enhancing the nutritional properties of foods. Among the phytonutrients, flavonoids have been shown to exert antibacterial effects by disrupting bacterial cell membrane functionality; however, the underlying molecular mechanisms remain elusive. In this study, we investigated the effect of quercetin on the cell membrane permeability of Staphylococcus aureus ATCC 27217. A combined metabolomic and transcriptomic approach was adopted to examine the regulatory mechanism of quercetin with respect to the fatty acid composition and associated genes. Kinetic analysis and molecular docking simulations were conducted to assess quercetin's inhibition of β-ketoacyl-acyl carrier protein reductase (FabG), a potential target in the bacterial fatty acid biosynthesis pathway. Metabolomic and transcriptomic results showed that quercetin increased the ratio of unsaturated to saturated fatty acids and the levels of membrane phospholipids. The bacteria reacted to quercetin-induced stress by attempting to enhance fatty acid biosynthesis; however, quercetin directly inhibited FabG activity, thereby disrupting bacterial fatty acid biosynthesis. These findings provide new insights into the mechanism of quercetin's effects on bacterial cell membranes and suggest potential applications for quercetin in bacterial inhibition.

Structural assembly of the bacterial essential interactome

The study of protein interactions in living organisms is fundamental for understanding biological processes and central metabolic pathways. Yet, our knowledge of the bacterial interactome remains limited. Here, we combined gene deletion mutant analysis with deep-learning protein folding using AlphaFold2 to predict the core bacterial essential interactome. We predicted and modeled 1402 interactions between essential proteins in bacteria and generated 146 high-accuracy models. Our analysis reveals previously unknown details about the assembly mechanisms of these complexes, highlighting the importance of specific structural features in their stability and function. Our work provides a framework for predicting the essential interactomes of bacteria and highlight the potential of deep-learning algorithms in advancing our understanding of the complex biology of living organisms. Also, the results presented here offer a promising approach to identify novel antibiotic targets.

The Molecular Basis of Catalysis by SDR Family Members Ketoacyl-ACP Reductase FabG and Enoyl-ACP Reductase FabI in Type-II Fatty Acid Biosynthesis

The short-chain dehydrogenase/reductase (SDR) superfamily members acyl-ACP reductases FabG and FabI are indispensable core enzymatic modules and catalytic orientation controllers in type-II fatty acid biosynthesis. Herein, we report their distinct substrate allosteric recognition and enantioselective reduction mechanisms. FabG achieves allosteric regulation of ACP and NADPH through ACP binding across two adjacent FabG monomers, while FabI follows an irreversible compulsory order of substrate binding in that NADH binding must precede that of ACP on a discrete FabI monomer. Moreover, FabG and FabI utilize a backdoor residue Phe187 or a "rheostat" α8 helix for acyl chain length selection, and their corresponding triad residues Ser142 or Tyr145 recognize the keto- or enoyl-acyl substrates, respectively, facilitating initiation of nucleophilic attack by NAD(P)H. The other two triad residues (Tyr and Lys) mediate subsequent proton transfer and (R)-3-hydroxyacyl- or saturated acyl-ACP production.

Adaptation Strategies to High Hydrostatic Pressures in Pseudothermotoga species Revealed by Transcriptional Analyses

Pseudothermotoga elfii strain DSM9442 and P. elfii subsp. lettingae strain DSM14385 are hyperthermophilic bacteria. P. elfii DSM9442 is a piezophile and was isolated from a depth of over 1600 m in an oil-producing well in Africa. P. elfii subsp. lettingae is piezotolerant and was isolated from a thermophilic bioreactor fed with methanol as the sole carbon and energy source. In this study, we analyzed both strains at the genomic and transcriptomic levels, paying particular attention to changes in response to pressure increases. Transcriptomic analyses revealed common traits of adaptation to increasing hydrostatic pressure in both strains, namely, variations in transport membrane or carbohydrate metabolism, as well as species-specific adaptations such as variations in amino acid metabolism and transport for the deep P. elfii DSM9442 strain. Notably, this work highlights the central role played by the amino acid aspartate as a key intermediate of the pressure adaptation mechanisms in the deep strain P. elfii DSM9442. Our comparative genomic and transcriptomic analysis revealed a gene cluster involved in lipid metabolism that is specific to the deep strain and that was differentially expressed at high hydrostatic pressures and might, thus, be a good candidate for a piezophilic gene marker in Pseudothermotogales.

Stairway to Stereoisomers: Engineering Short- and Medium-Chain Ketoreductases To Produce Chiral Alcohols

The short- and medium-chain dehydrogenase/reductase superfamilies are responsible for most chiral alcohol production in laboratories and industries. In nature, they participate in diverse roles such as detoxification, housekeeping, secondary metabolite production, and catalysis of several chemicals with commercial and environmental significance. As a result, they are used in industries to create biopolymers, active pharmaceutical intermediates (APIs), and are also used as components of modular enzymes like polyketide synthases for fabricating bioactive molecules. Consequently, random, semi-rational and rational engineering have helped transform these enzymes into product-oriented efficient catalysts. The rise of newer synthetic chemicals and their enantiopure counterparts has proved challenging, and engineering them has been the subject of numerous studies. However, they are frequently limited to the synthesis of a single chiral alcohol. The study attempts to defragment and describe hotspots of engineering short- and medium-chain dehydrogenases/reductases for the production of chiral synthons.

Functional Characterization and Synthetic Application of Is2-SDR, a Novel Thermostable and Promiscuous Ketoreductase from a Hot Spring Metagenome

In a metagenome mining-based search of novel thermostable hydroxysteroid dehydrogenases (HSDHs), enzymes that are able to selectively oxidize/reduce steroidal compounds, a novel short-chain dehydrogenase/reductase (SDR), named Is2-SDR, was recently discovered. This enzyme, found in an Icelandic hot spring metagenome, shared a high sequence similarity with HSDHs, but, unexpectedly, showed no activity in the oxidation of the tested steroid substrates, e.g., cholic acid. Despite that, Is2-SDR proved to be a very active and versatile ketoreductase, being able to regio- and stereoselectively reduce a diversified panel of carbonylic substrates, including bulky ketones, α- and β-ketoesters, and α-diketones of pharmaceutical relevance. Further investigations showed that Is2-SDR was indeed active in the regio- and stereoselective reduction of oxidized steroid derivatives, and this outcome was rationalized by docking analysis in the active site model. Moreover, Is2-SDR showed remarkable thermostability, with an apparent melting temperature (T_M) around 75 °C, as determined by circular dichroism analysis, and no significant decrease in catalytic activity, even after 5 h at 80 °C. A broad tolerance to both water-miscible and water-immiscible organic solvents was demonstrated as well, thus, confirming the potential of this new biocatalyst for its synthetic application.

Characterization of Two Dehydrogenases from Gluconobacter oxydans Involved in the Transformation of Patulin to Ascladiol

Patulin is a mycotoxin that primarily contaminate apples and apple products. Whole cell or cell-free extracts of Gluconobacter oxydans ATCC 621 were able to transform patulin to E-ascladiol. Proteins from cell-free extracts were separated by anion exchange chromatography and fractions with patulin transformation activity were subjected to peptide mass fingerprinting, enabling the identification of two NADPH dependent short chain dehydrogenases, GOX0525 and GOX1899, with the requisite activity. The genes encoding these enzymes were expressed in E. coli and purified. Kinetic parameters for patulin reduction, as well as pH profiles and thermostability were established to provide further insight on the potential application of these enzymes for patulin detoxification.

Lead derivatization of ethyl 6-bromo-2-((dimethylamino)methyl)-5-hydroxy-1-phenyl-1H-indole-3-carboxylate and 5-bromo-2-(thiophene-2-carboxamido) benzoic acid as FabG inhibitors targeting ESKAPE pathogens

Our previous studies on FabG have identified two compounds 5-bromo-2-(thiophene-2-carboxamido) benzoic acid (A) and ethyl 6-bromo-2-((dimethylamino)methyl)-5-hydroxy-1-phenyl-1H-indole-3-carboxylate(B) as best hits with allosteric mode of inhibition. FabG is an integral part of bacterial fatty acid biosynthetic system FAS II shown to be an essential gene in most ESKAPE Pathogens. The current work is focussed on lead expansion of these two hit molecules which ended up with forty-three analogues (twenty-nine analogues from lead compound A and fourteen compounds from lead compound B). The enzyme inhibition studies revealed that compound 15 (effective against EcFabG, AbFabG, StFabG, MtFabG1) and 19 (inhibiting EcFabG and StFabG) had potency of broad-spectrum inhibition on FabG panel.

Structural comparison of Acinetobacter baumannii β-ketoacyl-acyl carrier protein reductases in fatty acid and aryl polyene biosynthesis

Some Gram-negative bacteria harbor lipids with aryl polyene (APE) moieties. Biosynthesis gene clusters (BGCs) for APE biosynthesis exhibit striking similarities with fatty acid synthase (FAS) genes. Despite their broad distribution among pathogenic and symbiotic bacteria, the detailed roles of the metabolic products of APE gene clusters are unclear. Here, we determined the crystal structures of the β-ketoacyl-acyl carrier protein (ACP) reductase ApeQ produced by an APE gene cluster from clinically isolated virulent Acinetobacter baumannii in two states (bound and unbound to NADPH). An in vitro visible absorption spectrum assay of the APE polyene moiety revealed that the β-ketoacyl-ACP reductase FabG from the A. baumannii FAS gene cluster cannot be substituted for ApeQ in APE biosynthesis. Comparison with the FabG structure exhibited distinct surface electrostatic potential profiles for ApeQ, suggesting a positively charged arginine patch as the cognate ACP-binding site. Binding modeling for the aryl group predicted that Leu185 (Phe183 in FabG) in ApeQ is responsible for 4-benzoyl moiety recognition. Isothermal titration and arginine patch mutagenesis experiments corroborated these results. These structure-function insights of a unique reductase in the APE BGC in comparison with FAS provide new directions for elucidating host-pathogen interaction mechanisms and novel antibiotics discovery.