Evaluation of CV2025 ω-transaminase for the bioconversion of lignin breakdown products into value-added chemicals: synthesis of vanillylamine from vanillin

Abstract

Lignin is an essential component of the cell wall of various plants and represents an abundant and renewable natural resource. Both thermo-chemical and biological pre-treatment can be applied to break down the phenylpropanoid polymer subunits present in lignin. These liberate a range of phenolic compounds which represent potential substrates for bioconversion by ω-transaminases. In this work, the CV2025 ω-transaminase (ω-TAm) from Chromobacterium violaceum DSM30191, heterologously expressed in E. coli, was explored for selective amination of lignin breakdown intermediates into value-added products. Eight potential ω-TAm substrates were initially screened using (S)-α-methylbenzylamine (MBA) as the amino donor. Vanillin was identified as the best potential substrate which is converted into vanillylamine; an intermediate in the preparation of pelargonic acid vanillylamide used as a hyperemia inducing active substance in wound dressings. At low vanillin and MBA concentrations (< 10 mM) and with an excess of the amine donor (1:4 mol/mol) 100% w/w conversion of vanillin into vanillylamine was observed within 25 min. At vanillin concentrations above 10 mM, substrate inhibition was observed decreasing the rate and yield of the bioconversion. High concentrations of the reaction product (vanillylamine) and by-product (acetophenone) also limited the conversion due to increased backward reaction rate and inhibition. Vanillylamine synthesis could be carried out by both whole cell and clarified lysate forms of the CV2025 ω-TAm while fed-batch bioconversions (feeding low concentrations of both vanillin and MBA) could help overcome substrate inhibition and double the final product concentrations obtained. These results demonstrate the potential for bioconversion of lignin breakdown products into value-added chemicals but illustrate the need for enzymes with improved substrate range and implementation of techniques to overcome product inhibition and equilibrium constraints.     

Sister chromatid exchanges of human peripheral blood lymphocytes induced by N,N-diethylaniline in vitro

N,N-Diethylaniline is a reagent used in organic synthesis and is an important intermediate in the manufacturing of dyes. To evaluate its genotoxicity, we examined whether it can induce sister chromatid exchanges (SCEs) in human lymphocytes. We found that N,N-diethylaniline significantly increased the frequency of SCEs both in the absence and presence of S-9 mix. The SCEs from cultures treated by N,N-diethylaniline in the presence of S-9 mix displayed a marked increase which was about 5-fold greater than the control. ANOVA analyses indicated that there is a dose–response relationship between doses of N,N-diethylaniline and the frequency of SCEs, especially in the presence of S-9 mix. The results suggested that N,N-diethylaniline has genotoxicity.     

Lipase-catalyzed synthesis and antibacterial activity of N-vanillylnonanamide

N-vanillylnonanamide (VAN) was successfully synthesized from vanillylamine hydrochloride by enzymatic catalysis in supercritical carbon dioxide (SC–CO₂). Five commercial lipases, Novozyme 435, Lipozyme IM, Amano PS, Amano G and Sigma Candida cylindracea type VII, as biocatalysts for VAN synthesis were compared. Lipozyme IM exhibited best yields of tested lipases. Various parameters such as time, temperature, pressure and vanillylamine hydrochloride/nonanoic anhydride ratio that influenced the reaction were investigated. Nonanoic anhydride showed the best acyl donor of the employed substrates. An amidation yield of 40% was obtained when nonanoic anhydride and Lipozyme IM were used at 170 bar and 50 °C for 23 h in SC–CO₂. Besides, addition of 2 mM divalent salts (CuCl₂ and ZnCl₂) significantly increased 11–23% yield of the VAN. The enzyme operational stability suggested that Lipozyme IM maintained over 50 °C of the initial activity for the synthesis of VAN after reuse for 69 h. Furthermore, in vitro, VAN behaved as a potential antibacterial against Escherichia coli.     

Metabolic engineering of Pseudomonas putida for production of vanillylamine from lignin-derived substrates

Whole-cell bioconversion of technical lignins using Pseudomonas putida strains overexpressing amine transaminases (ATAs) has the potential to become an eco-efficient route to produce phenolic amines. Here, a novel cell growth-based screening method to evaluate the in vivo activity of recombinant ATAs towards vanillylamine in P. putida KT2440 was developed. It allowed the identification of the native enzyme Pp-SpuC-II and ATA from Chromobacterium violaceum (Cv-ATA) as highly active towards vanillylamine in vivo. Overexpression of Pp-SpuC-II and Cv-ATA in the strain GN442ΔPP_2426, previously engineered for reduced vanillin assimilation, resulted in 94- and 92-fold increased specific transaminase activity, respectively. Whole-cell bioconversion of vanillin yielded 0.70 ± 0.20 mM and 0.92 ± 0.30 mM vanillylamine, for Pp-SpuC-II and Cv-ATA, respectively. Still, amine production was limited by a substantial re-assimilation of the product and formation of the by-products vanillic acid and vanillyl alcohol. Concomitant overexpression of Cv-ATA and alanine dehydrogenase from Bacillus subtilis increased the production of vanillylamine with ammonium as the only nitrogen source and a reduction in the amount of amine product re-assimilation. Identification and deletion of additional native genes encoding oxidoreductases acting on vanillin are crucial engineering targets for further improvement.     

3-(1-Piperidinyl)alanine formation during the preparation ofC-terminal cysteine peptides with the Fmoc/t-Bu strategy

Summary Several side reactions have been detected for cysteine-containing peptides. During the synthesis ofC-terminal cysteine peptides, a base-catalyzed elimination of the sulfhydryl-protected side-chain to afford the dehydroalanine derivative followed by a nucleophilic addition to the alkene was observed. MALDI-TOF analysis was a useful analytical technique to determine this phenomenon.Abbreviations Acm acetamidomethyl - Boc tert-butyloxycarbonyl - t-Bu tert-butyl - DBU 1,8-diazabicyclo[5.4.0]undec-7-ene - DIEA N,N-diisopropylethylamine - DMF N,N-dimethylformamide - Fmoc 9-fluorenylmethyloxycarbonyl - HATU N-[(dimethylamino)-1H-1,2,3-triazolo[4,5-b]pyridin-1-yl-methylene]-N-methylmethanaminium hexafluorophosphateN-oxide - HBTU N-[(1H-benzotriazol-1-yl)(dimethylamino)methylene]-N-methylmethanaminium hexafluorophosphateN-oxide - HOAt 1-hydroxy-7-azabenzotriazole - HOBt 1-hydroxybenzotriazole - HPLC high-performance liquid chromatography - MALDI-TOF matrix-assisted laser desorption/ionization time-of-flight mass spectrometry - PAC 4-hydroxymethylphenoxyacetic acid handle - PAL 5-(4-(9-fluorenylmethyloxycarbonyl)aminomethyl-3,5-dimethoxy-phenoxy)valeric acid handle - PEG-PS polyethylene glycol-polystyrene graft supports - PS polystyrene - Reagent R TFA/thioanisole/1,2-ethanedithiol/anisole (90:5:3:2) - S-t-Bu S-tert-butyl mercapto - TFA trifluoroacetic acid - Trt triphenylmethyl. Amino acid symbols denote thel-configuration, unless indicated otherwise     

Synthesis of pentylferulate by a feruloyl esterase from Aspergillus niger using water-in-oil microemulsions

Pentylferulate synthesis was achieved at high yields (50–60%) with Aspergillus niger feruloyl esterase using a water-in-oil microemulsion system. The initial rate of synthesis decreased by 15–20% when the water content of the microemulsion was increased from 1.8 to 2.4% (v/v), although a concomitant decrease in conversion was not observed. The enzyme stability was significantly higher in the microemulsion than in an aqueous solution.     

Anti-Prelog Reduction of Prochiral Carbonyl Compounds by Oenococcus oeni in a Biphasic System

An aqueous-organic biphasic system was established and used with whole cells of Oenococcus oeni to reduce 2-octanone to (R)-2-octanol. The conversion reached 99% when the Tris/borate buffer was increased from 50 mM to 300 mM in the aqueous phase. In addition, the conversion increased as the log P value of the organic solvent changed from 0.5 to 6.6. Under optimized conditions, the conversion of (R)-2-octanol reached 99% from 0.5 M 2-octanone with an optical purity of 99% e.e. The biphasic system allows the anti-Prelog reduction of aliphatic and aromatic ketones to furnish (R)-configurated alcohols in high optical purity as well.     

Improved octyl glucoside synthesis using immobilized β-glucosidase on PA-M with reduced glucose surplus inhibition

A β-glucosidase extracted from bitter almond (Prunus dulcis var. amara) was immobilized on polyamine microspheres (PA-M) for catalytic octyl glucoside (OG) synthesis from glucose and octanol through reversed hydrolysis. The immobilization increased the activity of enzyme at pH 6.0–7.0, and the optimal reaction temperature for immobilized enzyme was identical to the free enzyme. The thermal stability and solvent tolerance of enzyme were increased by its immobilization. In the co-solvent system using 10% t-butyl alcohol and 10% (v/v) water, the yield of OG was increased by 1.7-fold compared to the yield from the system without co-solvent. Based on dynamic and Dixon plot analyses, the initial reaction velocity (V₀) increased approximately three-fold on immobilization and the OG synthesis was inhibited by surplus glucose. The inhibition dissociation constants for free and immobilized enzyme were 219?mM and 116?mM, respectively. A fed-batch mode was applied in the OG synthesis to minimize substrate inhibition. After 336?h of reaction, the OG yield and the conversion rate of glucose reached 134?mM and 59.6%, respectively. Compared to the batch operation, the fed-bath operation increased the OG yield and the conversion rate of glucose by 340% and 381%, respectively.     

Capsaicin hydrolysis by Candida antarctica lipase

Capsaicin was hydrolysed by lipase B from Candida antarctica into vanillylamine and 8-methyl-6-trans-nonenoic acid. Conversions of 70% were obtained after 72 h at 70 °C in water but decreased to only 15% when capsaicin was solubilized in 15% (v/v) ethanol/water after 72 h at 45 °C. No activity occurred in chloroform/water mixtures. According to our knowledge, this is the first report concerning amide hydrolysis by a lipase.     

3-Thiopropionic acid as a highly versatile multidetachable thioester resin linker

Summary This paper describes a practical new use of 3-mercaptopropionic acid as a highly versatile multidetachable linker for solid-phase synthesis. Our approach is based on the stability of the alkylthioester functionality to optimized Boc-SPPS protocols and HF treatment, as well as on the mild activation of the thioester functionality toward nucleophilic or reductive displacement. This allows several C-terminal modifications to be introduced into a synthetic molecule during the cleavage step. We have shown that unprotected peptides can be efficiently cleaved from a propyl thioester-polyethylene glycol-poly-(N,N-dimethylacrylamide) copolymer resin using a great variety of nucleophiles to give the corresponding C-terminally modified peptides (esters, thioesters, carboxylic acids, thioacids, amides, hydroxamic acids, hydrazides, alcohols). The nucleophilic cleavage reaction is both rapid and exceptionally clean in all the cases tested. Abbreviations: HBTU,N-[(1H-benzotriazol-1-yl)(dimethylamino)methylene]-N-methylmethanaminium hexafluorophosphateN-oxide); DIEA,N,N-diisopropylethylamine; DMF,N,N-dimethyl formamide; ES-MS, electrospray mass spectrometry; FAB-MS, fast atom bombardment mass spectrometry; HMBA, hydroxymethylbenzoic acid; HPLC, high performance liquid chromatography; PBS: phosphate buffer saline; PEGA, polyethylene glycolpoly-(N,N-dimethylacrylamide); TFA, trifluoroacetic acid; SPPS, solid-phase peptide synthesis. Standard IUPAC single and triple letter codes for amino acids are used throughout     

Aspergillus melleus protease-catalyzed peptide synthesis using the carbamoylmethyl ester as an acyl donor in 1,1,1,3,3,3-hexafluoro- 2-propanol/N,N-dimethylformamide

The coupling between the carbamoylmethyl ester of an N-protected amino acid or dipeptide (at 25 mM) and an amino acid amide (at 100 mM) was achieved using Aspergillus melleus protease in 1,1,1,3,3,3-hexafluoro-2-propanol/N,N-dimethylformamide (1:1, v/v); the coupling efficiencies were dependent largely on the combination of amino acid residues: e.g. the dipeptide yields after 48 h were for l-Ala + Gly, 100% and for l-Leu + l-Leu, 16%.     

Carboxypeptidase Y-Catalyzed Reaction in Systems Containing Organic Solvent

The effect of organic solvents on carboxypeptidase Y (a serine carboxypeptidase from yeast)-catalyzed hydrolysis of amino acid ester and peptide synthesis from N-acyl amino acid ester and amino acid amide was investigated.

The K_m value of ester hydrolysis increased with an increase in the solvent content. Dioxane was the most effective and dimethyl sulfoxide (DMSO) the least, whilst K_cat showed a tendency to increase slightly in N, N-dimethylformamide (DMF) and DMSO. For dioxane and acetonitrile (MeCN) a maximum was observed.

In peptide formation from Fua-Phe-OEt and Gly-NH₂, dioxane and MeCN supported high product yield at molar fractions smaller than ca. 0.05 but the yield decreased significantly at higher fractions, although a relatively constant selectivity (ratio of the peptide bond formed to the ester consumed) was maintained. DMSO gave rather low peptide yields and selectivity even at lower molar fractions. DMF showed an intermediate tendency.

An apparent saturation parameter of the amine component was evaluated and the dissociation constant of a complex between acyl-enzyme and amino acid amide (K_n), as well as the rate constant of aminolysis exerted by the amino acid amide bound correctly on the enzyme (K_n), was calculated by initial rate analysis of peptide formation. In contrast to K_m values, K_n decreased with increasing concentrations of organic cosolvent. while a suppressive effect was observed (except for DMSO) on the K_n parameter.

Effects of the solvent practically immiscible in water was also studied by use of the enzyme physically “immobilized” on glass beads.     

Effects of Long-Term Fertilization on Leaf Photosynthetic Characteristics and Grain Yield in Winter Wheat

Based on a 20-year fertilization experiment with wheat-maize double cropping system, the effects of different long-term fertilization treatments on leaf photosynthetic characteristics and grain yield in different winter wheat (Triticum aestivum L.) cultivars were studied in the growing seasons of 2000–2001 and 2001–2002. A total of nine fertilization treatments were implemented, i.e. no fertilizer (CK), N fertilizer (N), N and P fertilizers (NP), N and K fertilizers (NK), N, P, and K fertilizers (NPK), only organic manure (M), organic manure and N fertilizer (MN), organic manure and N and P fertilizers (MNP), and organic manure and N, P, and K fertilizers (MNPK). With the treatments of combined organic manure and inorganic fertilizers (TMI), net photosynthetic rate (P _N), maximal activity of photosystem 2, PS2 (F_v/F_m), and chlorophyll content (SPAD value) of flag leaves and leaf area index (LAI) were much higher at the mid grain filling stage (20 or 23 d post anthesis, DPA), and exhibited slower declines at the late grain filling stage (30 DPA), compared with the treatments of only inorganic fertilizers (TI). The maximal canopy photosynthetic traits expressed as P _N×LAI and SPAD×LAI at the mid grain filling stage were also higher in TMI than those in TI, which resulted in different grain yields in TMI and TI. Among the treatments of TMI or among the treatments of TI, both flag leaf and canopy photosynthetic abilities and yield levels increased with the supplement of inorganic nutrients (N, P, and K fertilizers), except for the treatment of NK. Under NK, soil contents of N and K increased while that of P decreased. Hence the unbalanced nutrients in soil from the improper input of nutrients in NK treatment were probably responsible for the reduced flag leaf and canopy photosynthetic characteristics and LAI, and for the fast declining of flag leaf photosynthetic traits during grain filling, resulting in the reduced yield of NK similar to the level of CK.     

A method for the facile solid-phase synthesis of gramicidin S and its analogs

Summary A simple method is described for the facile synthesis of gramicidin S and six other analogs, using standard solidphase synthetic technology and a single solution-phase cyclization step. The peptides were purified to homogeneity and characterized by plasma desorption time-of-flight mass spectrometry and NMR spectroscopy. Complete ¹H NMR assignments for all seven peptides (in aqueous solution) are presented. Unlike previous approaches, the presented method is simple, automatable, rapid (less than three days), high-yielding, requires no side-chain protection during cyclization, and appears to be generally applicable to the preparation of a variety of related head-to-tail cyclic peptides.Abbreviations Boc t-butyloxycarbonyl - BOP benzotriazoyl N-oxytris(dimethylamino)phosphonium hexafluorophosphate - Bzl benzyl - DCC N,N-dicyclohexylcarbodiimide - DCM dichloromethane - DIEA N,N-diisopropylethylamine - DMF N,N-dimethylformamide - DQF-COSY double-quantum-filtered correlation spectroscopy - DSS 2,2-dimethyl-2-silapentane-5-sulfonate, sodium salt - EDAC 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide - HBTU 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyl uronium hexafluorophosphate - HOBt 1-hydroxybenzotriazole - 4-MeBzl 4-methylbenzyl - NHS N-hydroxysuccinimide - NOESY nuclear Overhauser effect spectroscopy - PAM phenylacetamidomethyl (resin) - RP-HPLC reversed-phase high-performance liquid chromatography - TFA trifluoroacetic acid - TOCSY total correlation spectroscopy - Tos tosyl - Troc 2,2,2-trichloroethylcarbamate.     

Effect of organic cosolvent on kinetic resolution of tert-leucine by penicillin G acylase from Kluyvera citrophila

Penicillin G acylase (PGA) from Kluyvera citrophila immobilized on Amberzyml was used for enantioselective hydrolysis of N-phenylacetylated-dl-tert-leucine (N-Phac-dl-Tle) to produce l-tert-leucine (l-Tle). The effects of various organic cosolvents on hydrolysis of N-Phac-dl-Tle have been investigated in aqueous-cosolvent medium. It was founded that the rate of PGA-catalyzed reaction was significantly affected by the presence of 2% (v/v) organic cosolvent concentration. The initial rate fell with increasing logP of the cosolvent, but for logP values less than −0.24 the rate was faster than in purely aqueous medium. Additionally, the relative rate increases with the increase of dielectric constant (ε) of organic cosolvents. The yields of l-Tle in all aqueous-cosolvent systems were above 95% with the enantiomeric excess (ee) of >99%.     

Comparative study on methyl orange removal by growing cells and washed cell suspensions of <Emphasis Type="Italic">Lactobacillus casei</Emphasis> TISTR 1500

Lactobacillus casei TISTR 1500 possesses cytoplasmic azoreductase, and converts methyl orange to N,N-dimethyl-p-phenylenediamine and 4-aminobenzenesulfonic acid. In culture growth, the strain completely degraded methyl orange at 200 mg/l, even though the pH value was lower than 4. The decolorization was inhibited in the growing culture with 800 mg of the dye/l after incubation for 12 h. The percentage of decolorization and specific decolorization rate with 400 and 800 mg/l were 66 and 15%, and 14.2, and 8.7 mg/gCell/h, respectively. Additionally, a growing culture is more tolerant to a high initial dye concentration than when using washed cell suspensions supplied with only sucrose. Moreover, incubation of a low cell density in 600 μM of Na⁺ and 20 mM of sucrose increased the specific decolorization rate from 2.34 mg/gCell/h (without Na⁺) to 4.32 mg/gCell/h. However, Na⁺ had no effect on the enhancement of azoreductase activity in the reaction mixture.     

Effect of Solvents and Kinetic Parameters on Synthesis of Ethyl Propionate Catalysed by Poly (AAc-co-HPMA-cl-MBAm)-Matrix-Immobilized Lipase of Pseudomonas aeruginosa BTS-2.

Summary A purified alkaline thermo-tolerant bacterial lipase from Pseudomonas aeruginosa BTS-2 was immobilized on a poly (AAc-co-HPMA-cl-MBAm) hydrogel network. The hydrogel showed approximately 95% binding efficiency for lipase (specific activity 1.96 U mg⁻¹). The immobilized enzyme achieved 65.1% conversion of ethanol and propionic acid (100 mM each) into ethyl propionate in n-nonane at 65 °C in 9 h. When alkane of C-chain length lower than n-nonane was used as the organic solvent, the conversion of ethanol and propionic acid into ethyl propionate decreased with a decrease in the log P value of alkanes. The immobilized lipase retained approximately 30% of its original catalytic activity after five cycles of reuse for esterification of ethanol and propionic acid into ethyl propionate at temperature 65 °C in 3 h. Addition of a molecular sieve (3 ?) to the reaction mixture enhanced the formation of ethyl propionate to 89.3%. Moreover, ethanol and propionic acid when taken a molar ratio of 3:1 further promoted the conversion rate to 94%. However, an increase in the molar ratio of propionic acid with respect to ethanol resulted in a decline of ethyl propionate synthesis.     

Anaerobic degradation of betaine by marine Desulfobacterium strains

From enrichment cultures with betaine (20 mM) and sulfate (20 mM) as the substrates and intertidal mud as an inoculum, a betaine-oxidizing, sulfate-reducing bacterium (strain PM4) was isolated. Strain PM4 was an oval to rod-shaped, Gram-negative, motile bacterium, which was able to oxidize lactate completely to CO₂ and contained, during growth on betaine and sulfate, high activities of key enzymes of the acetyl CoA/CO dehydrogenase pathway (carbon monoxide dehydrogenase and formate dehydrogenase), but not of 2-oxo-glutarate dehydrogenase, a key enzyme of the citric acid cycle. On the basis of its morphological and physiological characteristics, strain PM4 was identified as a Desulfobacterium strain. Desulfobacterium PM4 grew on betaine with a doubling time of approximately 20 h at 30°C and produced N, N-dimethylglycine (in a 1:1 ratio) and sulfide as products. In this type of betaine metabolism one of the methyl groups of betaine is oxidized to CO₂ and the reducing equivalents generated are used for the reduction of sulfate. Desulfobacterium autotrophicum (DSM 3382) grew also on betaine and sulfate with the formation of N,N-dimethylglycine, sulfide and CO₂.     

Enzymatic enantioselective transcyanation of silicon-containing aliphatic ketone with (S)-hydroxynitrile lyase from Manihot esculenta

(S)-Hydroxynitrile lyase from Manihot esculenta (MeHNL) was shown for the first time to be able to catalyze the enantioselective transcyanation of acetyltrimethylsilane (ATMS) with acetone cyanohydrin to form (S)-2-trimethylsilyl-2-hydroxyl-propionitrile in an aqueous/organic biphasic system. To better understand the reaction, various influential variables were examined. The most suitable organic phase, optimal buffer pH, aqueous phase content, shaking rate, temperature, concentration of ATMS, acetone cyanohydrin and crude enzyme were diisopropyl ether (DIPE), 5.4, 13% (v/v), 190 rpm, 40°C, 10 mM, 20 mM, and 35 U/ml, respectively, under which the initial reaction rate, substrate conversion and product enantiomeric excess (e.e.) were 19.5 mM/h, 99.0% and 93.5%, respectively. A comparative study demonstrated that silicon atoms in the substrate had a great effect on the reaction, and that ATMS was a much better substrate for MeHNL than its carbon analogue 3,3-dimethyl-2-butanone (DMBO) with respect to the initial reaction rate, substrate conversion and product e.e. MeHNL has greater affinity towards ATMS than its carbon analogue as indicated by the much lower K_m. The activation energy of MeHNL-catalyzed transcyanation of ATMS was also markedly lower than that of DMBO. The silicon effect on the reaction was rationalized on the basis of the special characteristics of silicon atoms and the catalytic mechanism of MeHNL.