Substrate-dependent enantioselectivity of a novel hydantoinase from Arthrobacter aurescens DSM 3745: purification and characterization as new member of cyclic amidases

Chemical synthesis and enzymatic, stereoselective hydrolysis of a functionalized dihydropyrimidine for the synthesis of β-amino acids

A novel substrate, 6-(4-nitrophenyl)dihydropyrimidine-2,4(1H,3H)-dione (pNO₂PheDU), was chemically synthesized and analytically verified for the potential biocatalytic synthesis of enantiopure β-amino acids. The hydantoinase (EC 3.5.2.2) from Arthrobacter crystallopoietes DSM20117 was chosen to prove the enzymatic hydrolysis of this substrate, since previous investigations showed activities of this enzyme toward 6-monosubstituted dihydrouracils. Whole cell biotransformations with recombinant Escherichia coli expressing the hydantoinase showed degradation of pNO₂PheDU. Additionally, the corresponding N-carbamoyl-β-amino acid (NCarbpNO₂βPhe) was chemically synthesized, an HPLC-method with chiral stationary phases for detection of this product was established and thus (S)-enantioselectivity toward pNO₂PheDU has been shown. Consequently this novel substrate is a potential precursor for the enantiopure β-amino acid para-nitro-β-phenylalanine (pNO₂βPhe).

The stereoselectivity and hydrolysis efficiency of recombinant D-hydantoinase from Vigna angularis Against 5-benzylhydantoin derivatives with halogen and methyl substituents

The researches on D-hydantoinase activity and substrate specificity towards dihydropyrimidine and hydantoin derivatives have been carried out intensively over the last few decades. So far, the major efforts have focused on (R,S)-5-phenylhydantoin and (R,S)-5-(4-hydroxyphenyl)hydantoin, the most desirable D-hydantoinase substrates from pharmaceutical industry point of view. However, it was shown that D-hydantoinase is a substrate-dependent enzyme, and its activity and stereoselectivity towards 5-monosubstituted hydantoins varied significantly with the type of substrate and the source of the enzyme. The aim of this study was to estimate the substrate specificity of D-hydantoinase towards series of 5-benzylhydantoin derivatives with halogen and methyl substituents in the phenyl ring. The biotransformations were carried out by using commercial enzyme: immobilized, recombinant, cloned, and expressed in Escherichia coli D-hydantoinase from Vigna angularis (rD-HYD). All reactions were monitored by capillary electrophoresis (CE), and the conversion yields were calculated. Additionally, enantiomeric ratios of the obtained D-phenylalanine derivatives were estimated by chiral high-performance liquid chromatography (HPLC). Interestingly, the differences in the activities of examined enzyme towards particular 5-benzylhydantoin derivatives were observed. CE was also shown as a promising method for monitoring the hydrolysis of new substrates by D-hydantoinase and further analyzing of enzyme substrate specificity.

Biochemical and mutational studies of allantoinase from Bacillus licheniformis CECT 20T

Allantoinases (allantoin amidohydrolase, E.C. 3.5.2.5) catalyze the hydrolysis of the amide bond of allantoin to form allantoic acid, in those organisms where allantoin is not the final product of uric acid degradation. Despite their importance in the purine catabolic pathway, sequences of microbial allantoinases with proven activity are scarce, and only the enzyme from Escherichia coli (AllEco) has been studied in detail in the genomic era. In this work, we report the cloning, purification and characterization of the recombinant allantoinase from Bacillus licheniformis CECT 20T (AllBali). The enzyme was a homotetramer with an apparent Tm of 62 ± 1 °C. Optimal parameters for the enzyme activity were pH 7.5 and 50 °C, showing apparent Km and kcat values of 17.7 ± 2.7 mM and 24.4 ± 1.5 s(-1), respectively. Co(2+) proved to be the most effective cofactor, inverting the enantioselectivity of AllBali when compared to that previously reported for other allantoinases. The common ability of different cyclic amidohydrolases to hydrolyze distinct substrates to the natural one also proved true for AllBali. The enzyme was able to hydrolyze hydantoin, dihydrouracil and 5-ethyl-hydantoin, although at relative rates 3-4 orders of magnitude lower than with allantoin. Mutagenesis experiments suggest that S292 is likely implicated in the binding of the allantoin ring through the carbonyl group of the polypeptide main chain, which is the common mechanism observed in other members of the amidohydrolase family. In addition, our results suggest an allosteric effect of H2O2 toward allantoinase.

Process parameter optimization for hydantoinase-mediated synthesis of optically pure carbamoyl amino acids of industrial value using Pseudomonas aeruginosa resting cells

Hydantoinase-mediated enzymatic synthesis of optically pure carbamoyl amino acids was investigated as an environmentally friendly, energy-efficient alternative to the otherwise energy-intensive, polluting chemical synthesis. Hydantoinase-producing bacterial strain was identified as Pseudomonas aeruginosa by 16S rRNA gene sequencing and biochemical profiling using the BIOLOG Microbial Identification System. Hydantoinase activity was assessed using hydantoin analogs and 5-monosubstituted hydantoins as substrates in a colorimetric assay. The hydantoinase gene was PCR amplified using gene-specific primers and sequenced on an automated gene analyzer. Hydantoinase gene sequence of P. aeruginosa MCM B-887 revealed maximum homology of only 87 % with proven hydantoinase gene sequences in GenBank. MCM B-887 resting cells converted >99 % of substrate into N-carbamoyl amino acids under optimized condition at 42 °C, pH 8.0, and 100 mM substrate concentration in <120 min. Hydantoin hydrolyzing activity was D-selective and included broad substrate profile of 5-methyl hydantoin, 5-phenyl hydantoin, 5-hydroxyphenyl hydantoin, o-chlorophenyl hydantoin, as well as hydantoin analogs such as allantoin, dihydrouracil, etc. MCM B-887 resting cells may thus be suitable for bio-transformations leading to the synthesis of optically pure, unnatural carbamoyl amino acids of industrial importance.

One-step purification of insoluble hydantoinase overproduced in Escherichia coli

Over-expression of hydantoinase from Agrobacterium radiobacter NRRL B11291 (HDTar) results in the formation of insoluble aggregates in Escherichia coli. As previously reported, recombinant HDTar could be obtained in a homogeneous form using one chromatographic step. However, soluble proteins are required for the pre-treatment in several steps before proceeding to the chromatographic purification step. In this study, we reported a method based on artificial oil bodies (AOBs) to obtain homologous HDTar from its insoluble form in one step. By linkage of HDTar to intein-oleosin gene fusion, the tripartite fusion protein was over-expressed as aggregates in E. coli. Upon sonication, the mixture comprising plant oil and the insoluble fusion protein was readily assembled into AOBs. Further induction for peptide cleavage mediated by intein, the bound HDTar was liberated from AOBs, and the protein free of fusion tags was then recovered. As a result, refolded HDTar was amplified by over 300-fold. Obviously, this simplified method provides an efficient way to obtain HDTar with high yield and high purity.

The crystal structures of dihydropyrimidinases reaffirm the close relationship between cyclic amidohydrolases and explain their substrate specificity

In eukaryotes, dihydropyrimidinase catalyzes the second step of the reductive pyrimidine degradation, the reversible hydrolytic ring opening of dihydropyrimidines. Here we describe the three-dimensional structures of dihydropyrimidinase from two eukaryotes, the yeast Saccharomyces kluyveri and the slime mold Dictyostelium discoideum, determined and refined to 2.4 and 2.05 angstroms, respectively. Both enzymes have a (beta/alpha)8-barrel structural core embedding the catalytic di-zinc center, which is accompanied by a smaller beta-sandwich domain. Despite loop-forming insertions in the sequence of the yeast enzyme, the overall structures and architectures of the active sites of the dihydropyrimidinases are strikingly similar to each other, as well as to those of hydantoinases, dihydroorotases, and other members of the amidohydrolase superfamily of enzymes. However, formation of the physiologically relevant tetramer shows subtle but nonetheless significant differences. The extension of one of the sheets of the beta-sandwich domain across a subunit-subunit interface in yeast dihydropyrimidinase underlines its closer evolutionary relationship to hydantoinases, whereas the slime mold enzyme shows higher similarity to the noncatalytic collapsin-response mediator proteins involved in neuron development. Catalysis is expected to follow a dihydroorotase-like mechanism but in the opposite direction and with a different substrate. Complexes with dihydrouracil and N-carbamyl-beta-alanine obtained for the yeast dihydropyrimidinase reveal the mode of substrate and product binding and allow conclusions about what determines substrate specificity, stereoselectivity, and the reaction direction among cyclic amidohydrolases.

Evolutionary relationship and application of a superfamily of cyclic amidohydrolase enzymes

Cyclic amidohydrolases belong to a superfamily of enzymes that catalyze the hydrolysis of cyclic C-N bonds. They are commonly found in nucleotide metabolism of purine and pyrimidine. These enzymes share similar catalytic mechanisms and show considerable structural homologies, suggesting that they might have evolved from a common ancestral protein. Homology searches based on common mechanistic properties and three-dimensional protein structures provide clues to the evolutionary relationships of these enzymes. Among the superfamily of enzymes, hydantoinase has been highlighted by its potential for biotechnological applications in the production of unnatural amino acids. The enzymatic process for the production of optically pure amino acids consists of three enzyme steps: hydantoin racemase, hydantoinase, and N-carbamoylase. For efficient industrial application, some critical catalytic properties such as thermostability, catalytic activity, enantioselectivity, and substrate specificity require further improvement. To this end, isolation of new enzymes with desirable properties from natural sources and the optimization of enzymatic processes were attempted. A combination of directed evolution techniques and rational design approaches has made brilliant progress in the redesign of industrially important catalytic enzymes; this approach is likely to be widely applied to the creation of designer enzymes with desirable catalytic properties.

Enantioselective synthesis of (S)-2-amino-4-phenylbutanoic acid by the hydantoinase method

Biosynthesis of (S)-(+)-2-amino-4-phenylbutanoic acid (1) was performed by nonenantioselective hydantoinase and L-N-carbamoylase using racemic 5-[2-phenylethyl]-imidazolidine-2,4-dione (rac-2) as a substrate. The compounds involved in this biocatalysis process could be simultaneously resolved by high-performance liquid chromatography using Chirobiotic T column with a mobile phase of EtOH/H(2)O = 10/90 at pH 4.2-4.5. To our knowledge, this is the first report of the successful production of 1 by the combination of recombinant hydantoinase and L-N-carbamoylase.

Purification of industrial hydantoinase in one chromatographic step without affinity tag

Hydantoinase is used in industry as a biocatalyst for the production of optically pure D- or L-amino acids. Previously, homogeneous hydantoinase was obtained by multi-chromatographic purification procedures. Here, we reported a process that contained only a single chromatographic step to purify a recombinant hydantoinase to homogeneity. Hydantoinase from Agrobacterium radiobacter NRRL B11291 was expressed in Escherichia coli. The recombinant enzyme was purified following heat treatments, high concentration alcohol precipitation, and chelating Sephacel chromatography. The recombinant hydantoinase did not contain any affinity tags from the plasmid. This simplified procedure provided a convenient way to obtain hydantoinase in high yield (71%) and high purity. It should be very useful for further industrial application and for the study of the structure-function of hydantoinase.

Crystal structure of D-Hydantoinase from Burkholderia pickettii at a resolution of 2.7 Angstroms: insights into the molecular basis of enzyme thermostability

D-Hydantoinase (D-HYD) is an industrial enzyme that is widely used in the production of D-amino acids which are precursors for semisynthesis of antibiotics, peptides, and pesticides. This report describes the crystal structure of D-hydantoinase from Burkholderia pickettii (HYD(Bp)) at a 2.7-A resolution. The structure of HYD(Bp) consists of a core (alpha/beta)(8) triose phosphate isomerase barrel fold and a beta-sheet domain, and the catalytic active site consists of two metal ions and six highly conserved amino acid residues. Although HYD(Bp) shares only moderate sequence similarity with D-HYDs from Thermus sp. (HYD(Tsp)) and Bacillus stearothermophilus (HYD(Bst)), whose structures have recently been solved, the overall structure and the structure of the catalytic active site are strikingly similar. Nevertheless, the amino acids that compose the substrate-binding site are less conserved and have different properties, which might dictate the substrate specificity. Structural comparison has revealed insights into the molecular basis of the differential thermostability of D-HYDs. The more thermostable HYD(Tsp) contains more aromatic residues in the interior of the structure than HYD(Bp) and HYD(Bst). Changes of large aromatic residues in HYD(Tsp) to smaller residues in HYD(Bp) or HYD(Bst) decrease the hydrophobicity and create cavities inside the structure. HYD(Tsp) has more salt bridges and hydrogen-bonding interactions and less oxidation susceptible Met and Cys residues on the protein surface than HYD(Bp) and HYD(Bst). Besides, HYD(Tsp) also contains more rigid Pro residues. These factors are likely to make major contributions to the varying thermostability of these enzymes. This information could be exploited in helping to engineer more thermostable mesophilic enzymes.

Characterization and phylogenetic analysis of a thermostable N-carbamoyl- l-amino acid amidohydrolase from Bacillus kaustophilus CCRC11223

A thermostable N-carbamoyl- l-amino acid amidohydrolase ( l-N-carbamoylase) gene composed of an 1,230-bp ORF encoding a 44.3-kDa protein was cloned from the thermophile Bacillus kaustophilus CCRC11223. This l-N-carbamoylase contained six cysteine residues that form three disulfide bridges. The purified l-N-carbamoylase was stringently l-specific and exhibited high activity in the hydrolysis of N-carbamoyl- l-homophenylalanine. N-carbamoyl derivatives of beta-alanine, beta-aminoisobutyric acids, l-tryptophan, and d-specific amino acids were not recognized as substrates. The l-N-carbamoylase required the divalent metal ions Mn(2+), Co(2+), and Ni(2+) for increasing activity. The pH and temperature optima of the enzyme were pH 7.4 and 70 degrees C, respectively. This enzyme was completely thermostable at 50 degrees C for 36 days in the presence of d- and/or l-specific substrates. Phylogenetic analysis of the available amino acid sequences of N-carbamoyl and N-acyl amino acid amidohydrolases from the three main kingdoms of life showed that they can be divided into four distinct families. The B. kaustophilus enzyme could be classified into the family of l-N-carbamoylases and some beta-ureidopropionases, but did not hydrolyze beta-ureidopropionates.

Immobilization of the hydantoin cleaving enzymes from Arthrobacter aurescens DSM 3747

The immobilization procedure of the two industrially important hydantoin cleaving enzymes--hydantoinase and L-N-carbamoylase from Arthrobacter aurescens DSM 3747--was optimized. Using different methods (carbodiimide, epoxy activated carriers) it was possible to immobilize the crude hydantoinase from A. aurescens DSM 3747 to supports containing primary amino groups with a yield of up to 60%. Immobilization on more hydrophobic supports such as Eupergit C and C 250 L resulted in lower yields of activity, whereas the total protein coupled remained constant. All attempts to immobilize the crude L-N-carbamoylase resulted in only low activity yields. Therefore, the enzyme was highly purified and used in immobilization experiments. The pure enzyme could easily be obtained in large amounts by cultivation of a recombinant Escherichia coli strain following a three step purification protocol consisting of cell disruption, chromatography on Streamline diethylaminoethyl and Mono Q. The immobilization of the L-N-carbamoylase was optimized with respect to the coupling yield by varying the coupling method as well as the concentrations of protein, carrier and carbodiimide. Using 60 mM of water-soluble carbodiimide, nearly 100% of the enzyme activity and protein could be immobilized to EAH Sepharose 4B.

Optimization of the immobilization parameters and operational stability of immobilized hydantoinase and l-N-carbamoylase from Arthrobacter aurescens for the production of optically pure l-amino acids

2The immobilization parameters were optimized for the hydantoinase and the L-N-carbamoylase from Arthrobacter aurescens DSM 3747 or 3745, respectively. To optimize activity yields and specific activities for the immobilization to Eupergit C, Eupergit C 250 L, and EAH-Sepharose wild-type, recombinant and genetically modified ('tagged') enzymes were investigated concerning the influence of the protein concentration, the kind of support and the immobilization method. For both enzymes, the use of the recombinant proteins resulted in enhanced specific activities especially when using a hydrophilic support for immobilization such as Sepharose. In the case of a genetically modified hydantoinase carrying a His(6)-tag, affinity coupling led to a loss of activity of higher than 80%. Both enzymes were significantly stabilized by immobilization: In packed bed reactors, Eupergit C 250 L (NH(2))-immobilized hydantoinase and EAH-Sepharose-immobilized L-N-carbamoylase showed half-life times of approx. 14000 and 900 hours, respectively. Together with specific activities of the immobilized enzymes of 2.5 U/g wet carrier (hydantoinase) and 10 U/g wet carrier (L-N-carbamoylase) the newly developed biocatalysts are sufficient to fulfill industrial requirements.In comparison to the free enzymes, temperature and pH-optima were increased by 10 degrees C and one pH unit, respectively, after immobilization. The pH and temperature optima of the hydantoinase (L-N-carbamoylase) were determined to be pH 8.5-10 (pH 9.5) and 45-60 degrees C (60 degrees C).In order to provide sufficient amounts of biocatalyst for the process development in mini plant scale, a 50 fold scale-up of the optimized immobilization procedure was carried out for both enzymes. Because of the overlapping optima, both immobilized enzymes can be operated together in one reactor.

High-cell-density fermentation for production of L-N-carbamoylase using an expression system based on the Escherichia coli rhaBAD promoter

A high-cell-density fed-batch fermentation for the production of heterologous proteins in Escherichia coli was developed using the positively regulated Escherichia coli rhaBAD promoter. The expression system was improved by reducing of the amount of expensive L-rhamnose necessary for induction of the rhamnose promoter and by increasing the vector stability. Consumption of the inducer L-rhamnose was inhibited by inactivation of L-rhamnulose kinase encoding gene rhaB of Escherichia coli W3110, responsible for the first irreversible step in rhamnose catabolism. Plasmid instability caused by multimerization of the expression vector in the recombination-proficient W3110 was prevented by insertion of the multimer resolution site cer from the ColE1 plasmid into the vector. Fermentation experiments with the optimized system resulted in the production of 100 g x L(-1) cell dry weight and 3.8 g x L(-1) of recombinant L-N-carbamoylase, an enzyme, which is needed for the production of enantiomeric pure amino acids in a two-step reaction from hydantoins.

Development of an Escherichia coli whole cell biocatalyst for the production of L-amino acids

A whole cell biocatalyst for the enzymatic production of L-amino acids from hydantoins was created by coexpressing the genes encoding the L-hydantoinase, the L-N-carbamoylase and the hydantoin racemase from Arthrobacter aurescens in Escherichia coli. In order to construct a well balanced reaction system the enzymatic activity in the cells was varied by using vectors with different copy numbers for expression of the genes. Derivatives of pSC101, pACYC184 and pBR322 were employed for the various constructions and in one construct the hydantoinase gene was integrated into the E. coli chromosome. All constructs carried the E. coli rhamnose promoter system enabling gene expression control by transcriptional regulation. The productivity for L-tryptophan from the corresponding hydantoin was more than 6-fold higher than achieved with Arthrobacter aurescens.

Functional expression and characterization of the two cyclic amidohydrolase enzymes, allantoinase and a novel phenylhydantoinase, from Escherichia coli

A superfamily of cyclic amidohydrolases, including dihydropyrimidinase, allantoinase, hydantoinase, and dihydroorotase, all of which are involved in the metabolism of purine and pyrimidine rings, was recently proposed based on the rigidly conserved structural domains in identical positions of the related enzymes. With these conserved domains, two putative cyclic amidohydrolase genes from Escherichia coli, flanked by related genes, were identified and characterized. From the genome sequence of E. coli, the allB gene and a putative open reading frame, tentatively designated as a hyuA (for hydantoin-utilizing enzyme) gene, were predicted to express hydrolases. In contrast to allB, high-level expression of hyuA in E. coli of a single protein was unsuccessful even under various induction conditions. We expressed HyuA as a maltose binding protein fusion protein and AllB in its native form and then purified each of them by conventional procedures. allB was found to encode a tetrameric allantoinase (453 amino acids) which specifically hydrolyzes the purine metabolite allantoin to allantoic acid. Another open reading frame, hyuA, located near 64.4 min on the physical map and known as a UUG start, coded for D-stereospecific phenylhydantoinase (465 amino acids) which is a homotetramer. As a novel enzyme belonging to a cyclic amidohydrolase superfamily, E. coli phenylhydantoinase exhibited a distinct activity toward the hydantoin derivative with an aromatic side chain at the 5' position but did not readily hydrolyze the simple cyclic ureides. The deduced amino acid sequence of the novel phenylhydantoinase shared a significant homology (>45%) with those of allantoinase and dihydropyrimidinase, but its functional role still remains to be elucidated. Despite the unclear physiological function of HyuA, its presence, along with the allantoin-utilizing AllB, strongly suggested that the cyclic ureides might be utilized as nutrient sources in E. coli.

Hydantoin racemase from Arthrobacter aurescens DSM 3747: heterologous expression, purification and characterization

In Arthrobacter aurescens DSM 3747 three enzymes are involved in the complete conversion of slowly racemizing 5'-monosubstituted D,L-hydantoins to L-amino acids, a stereoselective hydantoinase, a stereospecific L-N-carbamoylase and a hydantoin racemase. The gene encoding the hydantoin racemase, designated hyuA, was identified upstream of the previously described L-N-carbamoylase gene in the plasmid pAW16 containing genomic DNA of A. aurescens. The gene hyuA which encodes a polypeptide of 25.1 kDa, was expressed in Escherichia coli and the recombinant protein purified to homogeneity and further characterized. The optimal condition for racemase activity were pH 8.5 and 55 degrees C with L-5-benzylhydantoin as substrate. The enzyme was completely inhibited by HgCL2 and iodoacetamide and stimulated by addition of dithiothreitol. No effect on enzyme activity was seen with EDTA. The enzyme showed preference for hydantoins with arylalkyl side chains. Kinetic studies revealed substrate inhibition towards the aliphatic substrate L-5-methylthioethylhydantoin. Enzymatic racemization of D-5-indolylmethylenehydantoin in D2O and NMR analysis showed that the hydrogen at the chiral center of the hydantoin is exchanged against solvent deuterium during the racemization.

Inverting enantioselectivity by directed evolution of hydantoinase for improved production of L-methionine

Using directed evolution, we have improved the hydantoinase process for production of L-methionine (L-met) in Escherichia coli. This was accomplished by inverting the enantioselectivity and increasing the total activity of a key enzyme in a whole-cell catalyst. The selectivity of all known hydantoinases for D-5-(2-methylthioethyl)hydantoin (D-MTEH) over the L-enantiomer leads to the accumulation of intermediates and reduced productivity for the L-amino acid. We used random mutagenesis, saturation mutagenesis, and screening to convert the D-selective hydantoinase from Arthrobacter sp. DSM 9771 into an L-selective enzyme and increased its total activity fivefold. Whole E. coli cells expressing the evolved L-hydantoinase, an L-N-carbamoylase, and a hydantoin racemase produced 91 mM L-met from 100 mM D,L-MTEH in less than 2 h. The improved hydantoinase increased productivity fivefold for >90% conversion of the substrate. The accumulation of the unwanted intermediate D-carbamoyl-methionine was reduced fourfold compared to cells with the wild-type pathway. Highly D-selective hydantoinase mutants were also discovered. Enantioselective enzymes rapidly optimized by directed evolution and introduced into multienzyme pathways may lead to improved whole-cell catalysts for efficient production of chiral compounds.

Purification of recombinant hydantoinase and L-N-carbamoylase from Arthrobacter aurescens expressed in Escherichia coli: comparison of wild-type and genetically modified proteins

Two enzymes, hydantoinase (HyuH) and L-N-carbamoylase (HyuC), are required for the biocatalytic production of natural and unnatural, optically pure L-amino acids starting from D,L-5-monosubstituted hydantoins using the so called 'hydantoinase-method'. For the preparation of immobilized enzymes, which omit several drawbacks of whole cell biocatalysts, purified or at least enriched HyuH and HyuC have to be provided. In order to simplify existing purification protocols several genetically modified derivatives of HyuH and HyuC from Arthrobacter aurescens DSM 3747 have been cloned and expressed in E. coli. A fusion protein consisting of maltose-binding protein (MalE) and HyuH resulted in an enhanced solubility of the hydantoinase, which easily forms inclusion bodies. On the other hand the fusion protein could easily be purified with high yield (76%) by just one chromatographic step (amylose resin) and the complex purification protocol of the wild-type enzyme could therefore be simplified and shortened significantly. Interestingly, the specific activity of the MalE-HyuH fusion protein was as high as the wild-type enzyme despite that the molecular mass was doubled. A second modification of HyuH carrying a histidine-tag was efficiently bound to a metal affinity matrix but inactivated completely during elution from the column at either low pH or in the presence of imidazole. In the case of HyuC, an aspartate-tag has been added to the biocatalyst to allow an integrated purification-immobilization procedure since this enzyme is immobilized efficiently only via its carboxylic groups. The diminished isoelectric point of the Asp-tagged HyuC resulted in a simplified purification procedure. Compared to the wild-type enzyme expressed in E. coli HyuC-Asp6 was shifted off the elution range of the contaminating proteins and higher purification factors were obtained even in the capturing step. In contrast to HyuH, it was possible to purify a L-N-carbamoylase carrying a histidine-tag to apparent homogeneity using immobilized metal affinity chromatography. Therefore, the existing three step purification protocol was reduced to one chromatographic step and the yield of this relatively unstable protein enhanced remarkably.

Biocatalysis for industrial production of fine chemicals

Chiral intermediates constitute a significant part of the fine chemicals market, which is strongly influenced by trends in the pharmaceutical industries, where approximately 70% of pharmaceuticals are expected to be enantiomerically pure in the next century as compared to 25% today. The main technologies by which enantiomerically pure ingredients are obtained today are (dynamic) resolutions of racemic mixtures. Asymmetric syntheses are being developed, but their applications in industry are still under represented. Biotechnological methods, resolutions as well as asymmetric syntheses, are becoming increasingly important in the industrial production of fine chemicals.