Functional Characterization of Epitheaflagallin 3-O-Gallate Generated in Laccase-Treated Green Tea Extracts in the Presence of Gallic Acid.

Epitheaflagallin (ETFG) and epitheaflagallin 3-O-gallate (ETFGg) are minor polyphenols in black tea extract that are enzymatically synthesized from epigallocatechin (EGC) and epigallocatechin gallate (EGCg), respectively, in green tea extract via laccase oxidation in the presence of gallic acid. The constituents of laccase-treated green tea extract in the presence of gallic acid are thus quite different from those of nonlaccase-treated green tea extract: EGC and EGCg are present in lower concentrations, and ETFG and ETFGg are present in higher concentrations. Additionally, laccase-treated green tea extract contains further polymerized catechin derivatives, comparable with naturally fermented teas such as oolong tea and black tea. We found that ETFGg and laccase-treated green tea extracts exhibit versatile physiological functions in vivo and in vitro, including antioxidative activity, pancreatic lipase inhibition, Streptococcus sorbinus glycosyltransferase inhibition, and an inhibiting effect on the activity of matrix metalloprotease-1 and -3 and their synthesis by human gingival fibroblasts. We confirmed that these inhibitory effects of ETFGg in vitro match well with the results obtained by docking simulations of the compounds with their target enzymes or noncatalytic protein. Thus, ETFGg and laccase-treated green tea extracts containing ETFGg are promising functional food materials with potential antiobesity and antiperiodontal disease activities.

Identification and characterization of a novel (-)-vibo-quercitol 1-dehydrogenase from Burkholderia terrae suitable for production of (-)-vibo-quercitol from 2-deoxy-scyllo-inosose.

(-)-vibo-Quercitol is a deoxyinositol (1L-1,2,4/3,5-cyclohexanepentol) that naturally occurs in oak species, honeydew honey, wines aged in oak barrels, and Gymnema sylvestre and is a potential intermediate for pharmaceuticals. We found that (-)-vibo-quercitol is stereoselectively synthesized from 2-deoxy-scyllo-inosose by the reductive reaction of a novel (-)-vibo-quercitol 1-dehydrogenase found in the proteomes of Burkholderia, Pseudomonas, and Arthrobacter. Among them, Burkholderia terrae sp. AKC-020 (40-1) produced a (-)-vibo-quercitol 1-dehydrogenase appropriate for synthesizing (-)-vibo-quercitol with a high diastereomeric excess. The enzyme was strongly induced in Bu. terrae cells when quercitol or 2-deoxy-scyllo-inosose was used as carbon source in the culture medium. The enzyme is NAD(H)-dependent and shows highly specific activity for (-)-vibo-quercitol and myo-inositol among the substrates tested. The enzyme gene (qudh) was obtained by PCR using degenerate primers based on the N-terminal and internal amino acid sequences of the purified enzyme, followed by thermal asymmetric interlaced PCR. The qudh gene showed homology with inositol 2-dehydrogenase (sharing 49.5% amino acid identity with IdhA from Sinorhizobium meliloti 1021). We successfully produced several recombinant (-)-vibo-quercitol 1-dehydrogenases and related enzymes identified by genome database mining using an Escherichia coli expression system. This revealed that scyllo-inositol dehydrogenase (IolX) in Bacillus subtilis can catalyze the reduction of 2-deoxy-scyllo-inosose to yield scyllo-quercitol, a stereoisomer of (-)-vibo-quercitol. Thus, we successfully identified two enzymes to produce both stereoisomers of deoxyinositols that are rare in nature.

Gene-specific amplicons from metagenomes as an alternative to directed evolution for enzyme screening: a case study using phenylacetaldehyde reductases.

Screening gene-specific amplicons from metagenomes (S-GAM) is a highly promising technique for the isolation of genes encoding enzymes for biochemical and industrial applications. From metagenomes, we isolated phenylacetaldehyde reductase (par) genes, which code for an enzyme that catalyzes the production of various Prelog's chiral alcohols. Nearly full-length par genes were amplified by PCR from metagenomic DNA, the products of which were fused with engineered par sequences at both terminal regions of the expression vector to ensure proper expression and then used to construct Escherichia coli plasmid libraries. Sequence- and activity-based screening of these libraries identified different homologous par genes, Hpar-001 to -036, which shared more than 97% amino acid sequence identity with PAR. Comparative characterization of these active homologs revealed a wide variety of enzymatic properties including activity, substrate specificity, and thermal stability. Moreover, amino acid substitutions in these genes coincided with those of Sar268 and Har1 genes, which were independently engineered by error-prone PCR to exhibit increased activity in the presence of concentrated 2-propanol. The comparative data from both approaches suggest that sequence information from homologs isolated from metagenomes is quite useful for enzyme engineering. Furthermore, by examining the GAM-based sequence dataset derived from soil metagenomes, we easily found amino acid substitutions that increase the thermal stability of PAR/PAR homologs. Thus, GAM-based approaches can provide not only useful homologous enzymes but also an alternative to directed evolution methodologies.

Characterization and cloning of laccase gene from Hericium coralloides NBRC 7716 suitable for production of epitheaflagallin 3-O-gallate.

Epitheaflagallin 3-O-gallate (ETFGg) is a minor polyphenol found in black tea extract, which has good physiological functions. It is synthesized from epigallocatechin gallate (EGCg) with gallic acid via laccase oxidation. Various basidiomycetes and fungi were screened to find a suitable laccase for the production of ETFGg. A basidiomycete, Hericium coralloides NBRC 7716, produced an appropriate extracellular laccase. The purified laccase produced twice the level of ETFGg compared with commercially available laccase from Trametes sp. The enzyme, termed Lcc2, is a monomeric protein with an apparent molecular mass of 67.2 kDa. The N-terminal amino acid sequence of Lcc2 is quite different from laccase isolated from the fruiting bodies of Hericium. Lcc2 showed similar substrate specificity to known laccases and could oxidize various phenolic substrates, including pyrogallol, gallic acid, and 2,6-dimethoxyphenol. The full-length lcc2 gene was obtained by PCR using degenerate primers, which were designed based on the N-terminal amino acid sequence of Lcc2 and conserved copper-binding sites of laccases, and 5'-, and 3'-RACE PCR with mRNA. The Lcc2 gene showed homology with Lentinula edodes laccase (sharing 77% amino acid identity with Lcc6). We successfully produced extracellular Lcc2 using a heterologous expression system with Saccharomyces cerevisiae. Moreover, it was confirmed that the recombinant laccase generates similar levels of ETFGg as the native enzyme.

Efficient PCR-based amplification of diverse alcohol dehydrogenase genes from metagenomes for improving biocatalysis: screening of gene-specific amplicons from metagenomes.

Screening of gene-specific amplicons from metagenomes (S-GAM) has tremendous biotechnological potential. We used this approach to isolate alcohol dehydrogenase (adh) genes from metagenomes based on the Leifsonia species adh gene (lsadh), the enzyme product of which can produce various chiral alcohols. A primer combination was synthesized by reference to homologs of lsadh, and PCR was used to amplify nearly full-length adh genes from metagenomic DNAs. All adh preparations were fused with lsadh at the terminal region and used to construct Escherichia coli plasmid libraries. Of the approximately 2,000 colonies obtained, 1,200 clones were identified as adh positive (∼60%). Finally, 40 adh genes, Hladh-001 to Hladh-040 (for homologous Leifsonia adh), were identified from 223 clones with high efficiency, which were randomly sequenced from the 1,200 clones. The Hladh genes obtained via this approach encoded a wide variety of amino acid sequences (8 to 99%). After screening, the enzymes obtained (HLADH-012 and HLADH-021) were confirmed to be superior to LSADH in some respects for the production of anti-Prelog chiral alcohols.

Gene cloning and characterization of two NADH-dependent 3-quinuclidinone reductases from Microbacterium luteolum JCM 9174.

We used the resting-cell reaction to screen approximately 200 microorganisms for biocatalysts which reduce 3-quinuclidinone to optically pure (R)-(-)-3-quinuclidinol. Microbacterium luteolum JCM 9174 was selected as the most suitable organism. The genes encoding the protein products that reduced 3-quinuclidinone were isolated from M. luteolum JCM 9174. The bacC gene, which consists of 768 nucleotides corresponding to 255 amino acid residues and is a constituent of the bacilysin synthetic gene cluster, was amplified by PCR based on homology to known genes. The qnr gene consisted of 759 nucleotides corresponding to 252 amino acid residues. Both enzymes belong to the short-chain alcohol dehydrogenase/reductase (SDR) family. The genes were expressed in Escherichia coli as proteins which were His tagged at the N terminus, and the recombinant enzymes were purified and characterized. Both enzymes showed narrow substrate specificity and high stereoselectivity for the reduction of 3-quinuclidinone to (R)-(-)-3-quinuclidinol.

Production of (R)-3-quinuclidinol by E. coli biocatalysts possessing NADH-dependent 3-quinuclidinone reductase (QNR or bacC) from Microbacterium luteolum and Leifsonia alcohol dehydrogenase (LSADH).

We found two NADH-dependent reductases (QNR and bacC) in Microbacterium luteolum JCM 9174 (M. luteolum JCM 9174) that can reduce 3-quinuclidinone to optically pure (R)-(-)-3-quinuclidinol. Alcohol dehydrogenase from Leifsonia sp. (LSADH) was combined with these reductases to regenerate NAD+ to NADH in situ in the presence of 2-propanol as a hydrogen donor. The reductase and LSADH genes were efficiently expressed in E. coli cells. A number of constructed E. coli biocatalysts (intact or immobilized) were applied to the resting cell reaction and optimized. Under the optimized conditions, (R)-(-)-3-quinuclidinol was synthesized from 3-quinuclidinone (15% w/v, 939 mM) giving a conversion yield of 100% for immobilized QNR. The optical purity of the (R)-(-)-3-quinuclidinol produced by the enzymatic reactions was >99.9%. Thus, E. coli biocatalysis should be useful for the practical production of the pharmaceutically important intermediate, (R)-(-)-3-quinuclidinol.

Gene cloning and characterization of dihydrolipoamide dehydrogenase from Microbacterium luteolum: A useful enzymatic regeneration system of NAD+ from NADH.

Dihydrolipoamide dehydrogenase (LPD), a useful biocatalyst for regenerating NAD(+), was purified from Microbacterium luteolum JCM 9174, and the gene encoding LPD was cloned from the genomic DNA. The gene contained an opening reading frame consisting of 1395 nucleotides encoding 465 amino acid residues with a predicted molecular weight of 49912.1 Da, which displayed 36-78% homology to known LPDs. Moreover, the FAD- and NAD(+)-binding sites and the two catalytic residues in the LPDs were conserved. The enzyme was expressed in recombinant Escherichia coli cells and purified to homogeneity by column chromatography. LPD of M. luteolum (MluLPD) accepted not only lipoamide but also some artificial electron acceptors such as dichlorophenolindophenol (DCIP) and nitrotetrazolium blue (NTB), that is, it functions as a diaphorase. NAD(+) demonstrated a strong activating effect on MluLPD, and the activity was 5.2 times higher than that without NAD(+). The enzyme was suitable for regenerating NAD(+) in biocatalytic reactions because of its high affinity for NADH (6.1 microM). An NAD(+)-regenerating system with MluLPD and laccase using 2,5-dimethoxy-1,4-benzoquinone as a hydrogen acceptor was demonstrated.

A novel thermophilic pectate lyase containing two catalytic modules of Clostridium stercorarium.

The Clostridium stercorarium F-9 pel9A gene encodes a pectate lyase Pel9A consisting of 1,240 amino acids with a molecular weight of 135,171. The mature form of Pel9A is a modular enzyme composed of two family-9 catalytic modules of polysaccharide lyases, CM9-1 and CM9-2, in order from the N terminus. Pel9A showed an overall sequence similarity to the hypothetical pectate lyase PelX of Bacillus halodurans (sequence identity 53%), and CM9-2 showed moderate sequence similarities to some pectate lyases of family 9. Sequence identity between CM9-1 and CM9-2 was 21.3%. The full-length Pel9A lacking the N-terminal signal peptide was expressed, purified, and characterized. The enzyme required Ca(2+) ion for its enzyme activity and showed high activity toward polygalacturonic acid but lower activity toward pectin, indicating that Pel9A is a pectate lyase. Immunological analysis using an antiserum raised against the purified enzyme indicated that Pel9A is constitutively synthesized by C. stercorarium F-9.