On the mechanism of a polyunsaturated fatty acid double bond isomerase from Propionibacterium acnes

Biomolecular investigations into BBI reveal an enzymatic mechanism for PUFA isomerisation in bifidobacterium CFA bioconversion strains

Multiple species of Bifidobacterium exhibit the ability to bioconvert conjugated fatty acids (CFAs), which is considered an important pathway for these strains to promote host health. However, there has been limited progress in understanding the enzymatic mechanism of CFA bioconversion by bifidobacteria, despite the increasing number of studies identifying CFA-producing strains. The protein responsible for polyunsaturated fatty acid (PUFA) isomerization in B. breve CCFM683 has recently been discovered and named BBI, providing a starting point for exploring Bifidobacterium isomerases (BIs). This study presents the sequence classification of membrane-bound isomerases from four common Bifidobacterium species that produce CFA. Heterologous expression, purification, and enzymatic studies of the typical sequences revealed that all possess a single c9, t11 isomer as the product and share common features in terms of enzymatic properties and catalytic kinetics. Using molecular docking and alanine scanning, Lys84, Tyr198, Asn202, and Leu245 located in the binding pocket were identified as critical to the catalytic activity, a finding further confirmed by site-directed mutagenesis-based screening assays. Overall, these findings provide insightful knowledge concerning the molecular mechanisms of BIs. This will open up additional opportunities for the use of bifidobacteria and CFAs in probiotic foods and precision nutrition.

Proteomics and Metabolomics Analysis Reveal the Regulation Mechanism of Linoleate Isomerase Activity and Function in Propionibacterium acnes

Conjugated linoleic acid (CLA) holds significant application prospects due to its anticancer, anti-atherosclerosis, lipid-lowering, weight-loss, and growth-promoting functions. The key to its efficient production lies in optimizing the biocatalytic performance of linoleic acid isomerase (LAI). Here, we constructed a Propionibacterium acnes mutant library and screened positive mutants with high linoleate isomerase activity. The proteomics and metabolomics were used to explore the mechanism in the regulation of linoleic acid isomerase activity. High-throughput proteomics revealed 104 differentially expressed proteins unique to positive mutant strains of linoleic acid isomerase of which 57 were upregulated and 47 were downregulated. These differentially expressed proteins were primarily involved in galactose metabolism, the phosphotransferase system, starch metabolism, and sucrose metabolism. Differential metabolic pathways were mainly enriched in amino acid biosynthesis, including glutamate metabolism, the Aminoacyl-tRNA biosynthesis pathway, and the ABC transporter pathway. The upregulated metabolites include dl-valine and Acetyl coA, while the downregulated metabolites include Glutamic acid and Phosphoenolpyruvate. Overall, the activity of linoleic acid isomerase in the mutant strain was increased by the regulation of key proteins involved in galactose metabolism, sucrose metabolism, and the phosphotransferase system. This study provides a theoretical basis for the development of high-yield CLA food.

Integrating data from spontaneous and induced trans-10 shift of ruminal biohydrogenation reveals discriminant bacterial community changes at the OTU level

Introduction

Microbial digestion is of key importance for ruminants, and disturbances can affect efficiency and quality of products for human consumers. Ruminal biohydrogenation of dietary unsaturated fatty acids leads to a wide variety of specific fatty acids. Some dietary conditions can affect the pathways of this transformation, leading to trans-10 fatty acids rather than the more usual trans-11 fatty acids, this change resulting in milk fat depression in dairy cows.

Materials and methods

We combined data from an induced and spontaneous trans-10 shift of ruminal biohydrogenation, providing new insight on bacterial changes at different taxonomic levels. A trans-10 shift was induced using dietary addition of concentrate and/or unsaturated fat, and the spontaneous milk fat depression was observed in a commercial dairy herd.

Results and discussion

Most changes of microbial community related to bacteria that are not known to be involved in the biohydrogenation process, suggesting that the trans-10 shift may represent the biochemical marker of a wide change of bacterial community. At OTU level, sparse discriminant analysis revealed strong associations between this change of biohydrogenation pathway and some taxa, especially three taxa belonging to [Eubacterium] coprostanoligenes group, Muribaculaceae and Lachnospiraceae NK3A20 group, that could both be microbial markers of this disturbance and candidates for studies relative to their ability to produce trans-10 fatty acids.

Antibiofilm activities of fatty acids including myristoleic acid against Cutibacterium acnes via reduced cell hydrophobicity

BACKGROUND

Cutibacterium acnes is a major colonizer and inhabitant of human skin and contributes to the pathogenesis of acne vulgaris. C. acnes either alone or with Staphylococcus aureus, which also inhabits skin, readily forms biofilms that are often tolerant of conventional antibiotics and the host immune system. It was hypothesized that the amphiphilic nature of some fatty acids (FAs) inhibit C. acnes or mixed biofilm formation.

PURPOSE

The antibacterial and antibiofilm activities of 24 saturated and unsaturated FAs were investigated against C. acnes as well as a mixture of the bacteria C. acnes and S. aureus.

METHODS

Anti-biofilm assays, antimicrobial assays, confocal laser scanning microscopy, scanning electron microscopy, extracellular polymeric substance production, and microbial adherence to hydrocarbon assay were utilized to elucidate how active FAs influence biofilm development.

RESULTS

Seventeen FAs at 20 µg/ml inhibited C. acnes biofilm formation by 60-99%. The minimum inhibitory concentrations (MICs) of 20 FAs were ≥ 500 µg/ml but 4 medium-chain FAs had MICs in a range 15 to 200 µg/ml. Interestingly, myristoleic acid inhibited biofilm formation at 1 μg/ml. Myristoleic acid also inhibited the formation of S. aureus and mixed C. acnes/S. aureus biofilms. FAs reduced C. acnes hydrophobicity and we found this was generally correlated with their antibiofilm forming efficacies. Transcriptional analyses showed that myristoleic acid modulates the expression of several biofilm-related genes such as lipase, hyaluronate lyase, and virulence-related genes.

CONCLUSION

This study shows myristoleic acid and other FAs inhibit biofilm formation by C. acnes and mixed biofilm formation by C. acnes and S. aureus. Hence, myristoleic acid might be useful for treating or preventing acne and C. acnes associated diseases.

A single amino acid substitution in the FAD-binding domain causes the inactivation of Propionibacterium Acnes isomerase

We previously demonstrated the efficient production of trans 10, cis 12-conjugated linoleic acid (t10c12-CLA) in Lactococcus lactis by ectopically expressing a Propionibacterium acnes isomerase (pai) gene and also mentioned that a recombinant strain was unable to accumulate t10c12-CLA product, despite the normal transcription. Here, the molecular analysis indicated that this mutated strain harbors a pai gene with a single-nucleotide mutation converting GC⁵⁰A to GTA, leading to a corresponding change of Alanine residue into Valine. The expression of the reverse mutation resulted in the recovery for enzyme activity. Site-directed mutagenesis indicated that the codon usage of Val¹⁷ was not responsible for the enzyme inactivation in the Ala¹⁷Val mutation. Western blot analysis revealed that the recombinant PAI protein was not detectable in the His tag-marked Ala¹⁷Val mutant. It is, therefore, reasonable to assume that Ala¹⁷ residue is critical for PAI functionality.Abbreviations: pai: propionibacterium acnes isomerase; CLA: conjugated linoleic acid; t10c12-CLA: trans 10, cis 12-CLA; LA: linoleic acid (18:2n-6); FAD: flavin adenine dinucleotide.

Genetic determinates for conjugated linolenic acid production in Lactobacillus plantarum ZS2058

AIMS

To investigate the genetic determinates for conjugated linolenic acid (CLNA) production in Lactobacillus plantarum ZS2058, a high CLNA producer.

METHODS AND RESULTS

After culturing with α-linolenic acid (ALA) in the medium, the fatty acid compositions of supernatant fluid and cell pellets were analysed via GC-MS. cis9,trans11,cis15-CLNA was identified to be the predominant isomer. And during CLNA production, 10-hydroxy-cis12-cis15-octadecenoic acid (10-HOEA) and 10-oxo-cis12-cis15-octadecenoic acid (10-OXOA) were accumulated. The E. coli recombinants harbouring genes encoding myosin-cross-reactive antigen (MCRA), short-chain dehydrogenase/oxidoreductase (DH) and acetoacetate decarboxylase (DC), respectively, were analysed for their roles in CLNA production. The results indicated that MCRA converted ALA to 10-HOEA, following converted to 10-OXOA by DH. While with the combination of three recombinants, ALA could be transformed into CLNA plus 10-HOEA and 10-OXOA. When the three genes were deleted, none of the L. plantarum ZS2058 knockout mutants could produce any CLNA, after complementation, and all the complementary mutants recovered the CLNA-production ability at similar levels as the wild strain.

CONCLUSIONS

Lactobacillus plantarum ZS2058 produced CLNA from ALA with 10-HOEA and 10-OXOA as intermediates. The triple-component isomerase of MCRA, DH and DC was the unique genetic determinant for CLNA generation.

SIGNIFICANCE AND IMPACT OF THE STUDY

The current results firstly provided conclusive evidence that the triple-component isomerase complex was shared by both CLA and CLNA production in lactobacilli.

Nitro-fatty acid formation and metabolism

Nitro-fatty acids (NO₂-FA) are pleiotropic modulators of redox signaling pathways. Their effects on inflammatory signaling have been studied in great detail in cell, animal and clinical models primarily using exogenously administered nitro-oleic acid. While we know a considerable amount regarding NO₂-FA signaling, endogenous formation and metabolism is relatively unexplored. This review will cover what is currently known regarding the proposed mechanisms of NO₂-FA formation, dietary modulation of endogenous NO₂-FA levels, pathways of NO₂-FA metabolism and the detection of NO₂-FA and corresponding metabolites.

Evidence for the Initial Steps of DHA Biohydrogenation by Mixed Ruminal Microorganisms from Sheep Involves Formation of Conjugated Fatty Acids

Incubation of DHA with sheep rumen fluid resulted in 80% disappearance in 6 h. The products were analyzed as their fatty acid (FA) methyl esters by GC-FID on SP-2560 and SLB-IL111 columns. The GC-online reduction × GC and GC-MS techniques demonstrated that all DHA metabolites retained the C22 structure (no evidence of chain-shortening). Two new transient DHA products were identified: mono-trans methylene interrupted-DHA and monoconjugated DHA (MC-DHA) isomers. Identification of MC-DHA was confirmed by their predicted elution using equivalent chain length differences from C18 FA, their molecular ions, and the 22:5 products formed which were the most abundant at 6 h. The 22:5 structures were established by fragmentation of their 4,4-dimethyloxazoline derivatives, and all 22:5 products contained an isolated double bond, suggesting formation via MC-DHA. The most abundant c4,c7,c10,t14,c19-22:5 appeared to be formed by unknown isomerases. Results suggest that the initial biohydrogenation of DHA was analogous to that of C18 FA.

Bacterial conjugated linoleic acid production and their applications

Conjugated linoleic acid (CLA) has been shown to exert various potential physiological properties including anti-carcinogenic, anti-obesity, anti-cardiovascular and anti-diabetic activities, and consequently has been considered as a promising food supplement. Bacterial biosynthesis of CLA is an attractive approach for commercial production due to its high isomer-selectivity and convenient purification process. Many bacterial species have been reported to convert free linoleic acid (LA) to CLA, hitherto only the precise CLA-producing mechanisms in Propionibacterium acnes and Lactobacillus plantarum have been illustrated completely, prompting the development of recombinant technology used in CLA production. The purpose of the article is to review the bacterial CLA producers as well as the recent progress on describing the mechanism of microbial CLA-production. Furthermore, the advances and potential in the heterologous expression of CLA genetic determinants will be presented.

Bacterial production of conjugated linoleic and linolenic Acid in foods: a technological challenge

Conjugated linoleic acid (CLA) and conjugated linolenic acid (CLNA) isomers are present in foods derived from ruminants as a result of the respective linoleic acid (LA) and α-linolenic acid (LNA) metabolism by ruminal microorganisms and in animals' tissues. CLA and CLNA have isomer-specific, health-promoting properties, including anticarcinogenic, antiatherogenic, anti-inflammatory, and antidiabetic activity, as well as the ability to reduce body fat. Besides ruminal microorganisms, such as Butyrivibrio fibrisolvens, many food-grade bacteria, such as bifidobacteria, lactic acid bacteria (LAB), and propionibacteria, are able to convert LA and LNA to CLA and CLNA, respectively. Linoleate isomerase activity, responsible for this conversion, is strain-dependent and probably related to the ability of the producer strain to tolerate the toxic effects of LA and LNA. Since natural concentrations of CLA and CLNA in ruminal food products are relatively low to exert their health benefits, food-grade bacteria with linoleate isomerase activity could be used as starter or adjunct cultures to develop functional fermented dairy and meat products with increased levels of CLA and CLNA or included in fermented products as probiotic cultures. However, results obtained so far are below expectations due to technological bottlenecks. More research is needed to assess if bacterial production kinetics can be increased and can match food processing requirements.

Sources and Bioactive Properties of Conjugated Dietary Fatty Acids

The group of conjugated fatty acids known as conjugated linoleic acid (CLA) isomers have been extensively studied with regard to their bioactive potential in treating some of the most prominent human health malignancies. However, CLA isomers are not the only group of potentially bioactive conjugated fatty acids currently undergoing study. In this regard, isomers of conjugated α-linolenic acid, conjugated nonadecadienoic acid and conjugated eicosapentaenoic acid, to name but a few, have undergone experimental assessment. These studies have indicated many of these conjugated fatty acid isomers commonly possess anti-carcinogenic, anti-adipogenic, anti-inflammatory and immune modulating properties, a number of which will be discussed in this review. The mechanisms through which these bioactivities are mediated have not yet been fully elucidated. However, existing evidence indicates that these fatty acids may play a role in modulating the expression of several oncogenes, cell cycle regulators, and genes associated with energy metabolism. Despite such bioactive potential, interest in these conjugated fatty acids has remained low relative to the CLA isomers. This may be partly attributed to the relatively recent emergence of these fatty acids as bioactives, but also due to a lack of awareness regarding sources from which they can be produced. In this review, we will also highlight the common sources of these conjugated fatty acids, including plants, algae, microbes and chemosynthesis.

Functional characterization of a fatty acid double-bond hydratase from Lactobacillus plantarum and its interaction with biosynthetic membranes

Hydrogenation of linoleic acid and other polyunsaturated fatty acids is a detoxification mechanism that is present in the Lactobacillus genus of lactic bacteria. The first stage in this multi-step process is hydration of the substrate with formation of 10-hydroxy-9-cis-octadecenoic acid due to fatty-acid hydratase activity that has been detected only in the membrane-associated cell fraction; however, its interaction with the cell membrane is unknown. To provide information in this respect we characterized the homotrimeric 64.7 kDa-native protein from Lactobacillus plantarum; afterwards, it was reconstituted in proteoliposomes and analyzed by confocal fluorescence microscopy. The results showed that hydratase is an extrinsic-membrane protein and hence, the enzymatic reaction occurs at the periphery of the cell. This location may be advantageous in the detoxifying process since the toxic linoleic acid molecule can be bound to hydratase and converted to non-toxic 10-hydroxy-9-cis-octadecenoic acid before it reaches cell membrane. Additionally, we propose that the interaction with membrane periphery occurs through electrostatic contacts. Finally, the structural model of L. plantarum hydratase was constructed based on the amino acid sequence and hence, the putative binding sites with linoleic acid were identified: site 1, located in an external hydrophobic pocket at the C-terminus of the protein and site 2, located at the core and in contact with a FAD molecule. Interestingly, it was found that the linoleic acid molecule arranges around a methionine residue in both sites (Met154 and Met81, respectively) that acts as a rigid pole, thus playing a key role in binding unsaturated fatty acids.

Identification and characterization of an oleate hydratase-encoding gene from Bifidobacterium breve

Bifidobacteria are common commensals of the mammalian gastrointestinal tract. Previous studies have suggested that a bifidobacterial myosin cross reactive antigen (MCRA) protein plays a role in bacterial stress tolerance, while this protein has also been linked to the biosynthesis of conjugated linoleic acid (CLA) in bifidobacteria. In order to increase our understanding on the role of MCRA in bifidobacteria we created and analyzed an insertion mutant of the MCRA-encoding gene of B. breve NCFB 2258. Our results demonstrate that the MCRA protein of B. breve NCFB 2258 does not appear to play a role in CLA production, yet is an oleate hydratase, which contributes to bifidobacterial solvent stress protection.

Crystal structure analysis of a fatty acid double-bond hydratase from Lactobacillus acidophilus

Bacteria have evolved mechanisms for the hydrogenation of unsaturated fatty acids. Hydroxy fatty acid formation may be the first step in such a process; however, knowledge of the structural and mechanistic aspects of this reaction is scarce. Recently, myosin cross-reactive antigen was shown to be a bacterial FAD-containing hydratase which acts on the 9Z and 12Z double bonds of C16 and C18 non-esterified fatty acids, with the formation of 10-hydroxy and 10,13-dihydroxy fatty acids. These fatty acid hydratases form a large protein family which is conserved across Gram-positive and Gram-negative bacteria with no sequence similarity to any known protein apart from the FAD-binding motif. In order to shed light on the substrate recognition and the mechanism of the hydratase reaction, the crystal structure of the hydratase from Lactobacillus acidophilus (LAH) was determined by single-wavelength anomalous dispersion. Crystal structures of apo LAH and of LAH with bound linoleic acid were refined at resolutions of 2.3 and 1.8 Å, respectively. LAH is a homodimer; each protomer consists of four intricately connected domains. Three of them form the FAD-binding and substrate-binding sites and reveal structural similarity to three domains of several flavin-dependent enzymes, including amine oxidoreductases. The additional fourth domain of LAH is located at the C-terminus and consists of three α-helices. It covers the entrance to the hydrophobic substrate channel leading from the protein surface to the active site. In the presence of linoleic acid, the fourth domain of one protomer undergoes conformational changes and opens the entrance to the substrate-binding channel of the other protomer of the LAH homodimer. The linoleic acid molecule is bound at the entrance to the substrate channel, suggesting movement of the lid domain triggered by substrate recognition.

Applications of stereospecifically-labeled Fatty acids in oxygenase and desaturase biochemistry

Oxygenation and desaturation reactions are inherently associated with the abstraction of a hydrogen from the fatty acid substrate. Since the first published application in 1965, stereospecific placement of a labeled hydrogen isotope (deuterium or tritium) at the reacting carbons has proven a highly effective strategy for investigating the chemical mechanisms catalyzed by lipoxygenases, hemoprotein fatty acid dioxygenases including cyclooxygenases, cytochromes P450, and also the desaturases and isomerases. This review presents a synopsis of all published studies through 2010 on the synthesis and use of stereospecifically labeled fatty acids (71 references), and highlights some of the mechanistic insights gained by application of stereospecifically labeled fatty acids.

Myosin-cross-reactive antigen (MCRA) protein from Bifidobacterium breve is a FAD-dependent fatty acid hydratase which has a function in stress protection

Background

The aim of this study was to determine the catalytic activity and physiological role of myosin-cross-reactive antigen (MCRA) from Bifidobacterium breve NCIMB 702258. MCRA from B. breve NCIMB 702258 was cloned, sequenced and expressed in heterologous hosts (Lactococcus and Corynebacterium) and the recombinant proteins assessed for enzymatic activity against fatty acid substrates.

Results

MCRA catalysed the conversion of palmitoleic, oleic and linoleic acids to the corresponding 10-hydroxy fatty acids, but shorter chain fatty acids were not used as substrates, while the presence of trans-double bonds and double bonds beyond the position C12 abolished hydratase activity. The hydroxy fatty acids produced were not metabolised further. We also found that heterologous Lactococcus and Corynebacterium expressing MCRA accumulated increasing amounts of 10-HOA and 10-HOE in the culture medium. Furthermore, the heterologous cultures exhibited less sensitivity to heat and solvent stresses compared to corresponding controls.

Conclusions

MCRA protein in B. breve can be classified as a FAD-containing double bond hydratase, within the carbon-oxygen lyase family, which may be catalysing the first step in conjugated linoleic acid (CLA) production, and this protein has an additional function in bacterial stress protection.

A bisallylic mini-lipoxygenase from cyanobacterium Cyanothece sp. that has an iron as cofactor

Lipoxygenases are enzymes that are found ubiquitously in higher animals and plants, but have only recently been identified in a number of bacteria. The genome of the diazotrophic unicellular cyanobacterium Cyanothece sp. harbors two genes with homology to lipoxygenases. Here we describe the isolation of one gene, formerly named csplox2. It was cloned, and the protein was expressed in Escherichia coli and purified. The purified enzyme belongs to the group of prokaryotic mini lipoxygenases, because it had a molecular mass of 65 kDa. Interestingly, it catalyzed the conversion of linoleic acid, the only endogenously found polyunsaturated fatty acid, primarily to the bisallylic hydroperoxide 11R-hydroperoxyoctadecadienoic acid. This product had previously only been described for the manganese lipoxygenase from the take all fungus, Gaeumannomyces graminis. By contrast, CspLOX2 was shown to be an iron lipoxygenase. In addition, CspLOX2 formed a mixture of typical conjugated lipoxygenase products, e.g. 9R- and 13S-hydroperoxide. The conversion of linoleic acid took place with a maximum reaction rate of 31 s(-1). Incubation of the enzyme with [(11S)-(2)H]linoleic acid led to the formation of hydroperoxides that had lost the deuterium label, thus suggesting that CspLOX2 catalyzes antarafacial oxygenation as opposed to the mechanism of manganese lipoxygenase. CspLOX2 could also oxidize diarachidonylglycerophosphatidylcholine with similar specificity as the free fatty acid, indicating that binding of the substrate takes place with a "tail-first" orientation. We conclude that CspLOX2 is a novel iron mini-lipoxygenase that catalyzes the formation of bisallylic hydroperoxide as the major product.

Myosin cross-reactive antigen of Streptococcus pyogenes M49 encodes a fatty acid double bond hydratase that plays a role in oleic acid detoxification and bacterial virulence

The myosin cross-reactive antigen (MCRA) protein family is highly conserved among different bacterial species ranging from Gram-positive to Gram-negative bacteria. Besides their ubiquitous occurrence, knowledge about the biochemical and physiological function of MCRA proteins is scarce. Here, we show that MCRA protein from Streptococcus pyogenes M49 is a FAD enzyme, which acts as hydratase on (9Z)- and (12Z)-double bonds of C-16, C-18 non-esterified fatty acids. Products are 10-hydroxy and 10,13-dihydroxy fatty acids. Kinetic analysis suggests that FAD rather stabilizes the active conformation of the enzyme and is not directly involved in catalysis. Analysis of S. pyogenes M49 grown in the presence of either oleic or linoleic acid showed that 10-hydroxy and 10,13-dihydroxy derivatives were the only products. No further metabolism of these hydroxy fatty acids was detected. Deletion of the hydratase gene caused a 2-fold decrease in minimum inhibitory concentration against oleic acid but increased survival of the mutant strain in whole blood. Adherence and internalization properties to human keratinocytes were reduced in comparison with the wild type. Based on these results, we conclude that the previously identified MCRA protein can be classified as a FAD-containing double bond hydratase, within the carbon-oxygen lyase family, that plays a role in virulence of at least S. pyogenes M49.