Mixing and matching methylotrophic enzymes to design a novel methanol utilization pathway in E. coli.

One-carbon (C1) compounds, such as methanol, have recently gained attention as alternative low-cost and non-food feedstocks for microbial bioprocesses. Considerable research efforts are thus currently focused on the generation of synthetic methylotrophs by transferring methanol assimilation pathways into established bacterial production hosts. In this study, we used an iterative combination of dry and wet approaches to design, implement and optimize this metabolic trait in the most common chassis, E. coli. Through in silico modelling, we designed a new route that "mixed and matched" two methylotrophic enzymes: a bacterial methanol dehydrogenase (Mdh) and a dihydroxyacetone synthase (Das) from yeast. To identify the best combination of enzymes to introduce into E. coli, we built a library of 266 pathway variants containing different combinations of Mdh and Das homologues and screened it using high-throughput 13C-labeling experiments. The highest level of incorporation of methanol into central metabolism intermediates (e.g. 22% into the PEP), was obtained using a variant composed of a Mdh from A. gerneri and a codon-optimized version of P. angusta Das. Finally, the activity of this new synthetic pathway was further improved by engineering strategic metabolic targets identified using omics and modelling approaches. The final synthetic strain had 1.5 to 5.9 times higher methanol assimilation in intracellular metabolites and proteinogenic amino acids than the starting strain did. Broadening the repertoire of methanol assimilation pathways is one step further toward synthetic methylotrophy in E. coli.

Engineering the expression system for Komagataella phaffii (Pichia pastoris): an attempt to develop a methanol-free expression system.

The construction of a methanol-free expression system of Komagataella phaffii (Pichia pastoris) was attempted by engineering a strong methanol-inducible DAS1 promoter using Citrobacter braakii phytase production as a model case. Constitutive expression of KpTRM1, formerly PRM1-a positive transcription regulator for methanol-utilization (MUT) genes of K. phaffii,was demonstrated to produce phytase without addition of methanol, especially when a DAS1 promoter was used but not an AOX1 promoter. Another positive regulator, Mxr1p, did not have the same effect on the DAS1 promoter, while it was more effective than KpTrmp1 on the AOX1 promoter. Removing a potential upstream repression sequence (URS) and multiplying UAS1DAS1 in the DAS1 promoter significantly enhanced the yield of C. braakii phytase with methanol-feeding, which surpassed the native AOX1 promoter by 80%. However, multiplying UAS1DAS1 did not affect the yield of methanol-free expression by constitutive KpTrm1p. Another important region to enhance the effect of KpTrm1p under a methanol-free condition was identified in the DAS1 promoter, and was termed ESPDAS1. Nevertheless, methanol-free phytase production using an engineered DAS1 promoter outperformed phytase production with the GAP promoter by 25%. Difference in regulation by known transcription factors on the AOX1 promoter and the DAS1 promoter was also illustrated.

Activity Essential Residue Analysis of Taxoid 10ß-O-Acetyl Transferase for Enzymatic Synthesis of Baccatin.

Taxoid 10ß-O-acetyl transferase (DBAT) is a key enzyme in the biosynthesis of the famous anticancer drug paclitaxel, which catalyses the formation of baccatin III from 10-deacetylbaccatin III (10-DAB). However, the activity essential residues of the enzyme are still unknown, and the acylation mechanism from its natural substrate 10-deacetylbaccatin III and acetyl CoA to baccatin III remains unclear. In this study, the homology modelling, molecular docking, site-directed mutagenesis, and kinetic parameter determination of the enzyme were carried out. The results showed that the enzyme mutant DBATH162A resulted in complete loss of enzymatic activity, suggesting that the residue histidine at 162 was essential to DBAT activity. Residues D166 and R363 which were located in the pocket of the enzyme by homology modelling and molecular docking were also important for DBAT activity through the site-directed mutations. Furthermore, four amino acid residues including S31 and D34 from motif SXXD, D372 and G376 from motif DFGWG also played important roles on acylation. This was the first report of the elucidation of the activity essential residues of DBAT, making it possible for the further structural-based re-design of the enzyme for efficient biotransformation of baccatin III and paclitaxel.

Complete Tetrasaccharide Repeat Unit Biosynthesis of the Immunomodulatory Bacteroides fragilis Capsular Polysaccharide A.

Capsular polysaccharide A (CPSA) is a four-sugar repeating unit polymer found on the surface of the gut symbiont Bacteroides fragilis that has therapeutic potential in animal models of autoimmune disorders. This therapeutic potential has been credited to its zwitterionic character derived from a positively charged N-acetyl-4-aminogalactosamine (AADGal) and a negatively charged 4,6-O-pyruvylated galactose (PyrGal). In this report, using a fluorescent polyisoprenoid chemical probe, the complete enzymatic assembly of the CPSA tetrasaccharide repeat unit is achieved. The proposed pyruvyltransferase, WcfO; galactopyranose mutase, WcfM; and glycosyltransferases, WcfP and WcfN, encoded by the CPSA biosynthesis gene cluster were heterologously expressed and functionally characterized. Pyruvate modification, catalyzed by WcfO, was found to occur on galactose of the polyisoprenoid-linked disaccharide (AADGal-Gal), and did not occur on galactose linked to uridine diphosphate (UDP) or a set of nitrophenyl-galactose analogues. This pyruvate modification was also found to be required for the incorporation of the next sugar in the pathway N-acetylgalactosamine (GalNAc) by the glycosyltransferase WcfP. The pyruvate acetal modification of a galactose has not been previously explored in the context of a polysaccharide biosynthesis pathway, and this work demonstrates the importance of this modification to repeat unit assembly. Upon production of the polyisoprenoid-linked AADGal-PyrGal-GalNAc, the proteins WcfM and WcfN were found to work in concert to form the final tetrasaccharide, where WcfM formed UDP-galactofuranose (Galf) and WcfN transfers Galf to the AADGal-PyrGal-GalNAc. This work demonstrates the first enzymatic assembly of the tetrasaccharide repeat unit of CPSA in a sequential single pot reaction.

A rationally engineered yeast pyruvyltransferase Pvg1p introduces sialylation-like properties in neo-human-type complex oligosaccharide.

Pyruvylation onto the terminus of oligosaccharide, widely seen from prokaryote to eukaryote, confers negative charges on the cell surface and seems to be functionally similar to sialylation, which is found at the end of human-type complex oligosaccharide. However, detailed molecular mechanisms underlying pyruvylation have not been clarified well. Here, we first determined the crystal structure of fission yeast pyruvyltransferase Pvg1p at a resolution of 2.46 Å. Subsequently, by combining molecular modeling with mutational analysis of active site residues, we obtained a Pvg1p mutant (Pvg1p(H168C)) that efficiently transferred pyruvyl moiety onto a human-type complex glycopeptide. The resultant pyruvylated human-type complex glycopeptide recognized similar lectins on lectin arrays as the α2,6-sialyl glycopeptides. This newly-generated pyruvylation of human-type complex oligosaccharides would provide a novel method for glyco-bioengineering.

Comparison of transposon and deletion mutants in Mycobacterium tuberculosis: The case of rv1248c, encoding 2-hydroxy-3-oxoadipate synthase.

We compared phenotypes of five strains of Mycobacterium tuberculosis (Mtb) differing in their expression of rv1248c and its product, 2-hydroxy-3-oxoadipate synthase (HOAS), with a focus on carbon source-dependent growth rates and attenuation in mice. Surprisingly, an rv1248c transposon mutant on a CDC1551 background grew differently than an rv1248c deletion mutant on the same background. Moreover, the same rv1248c deletion in two different yet genetically similar strain backgrounds (CDC1551 and H37Rv) gave different phenotypes, though each could be complemented. Whole genome re-sequencing did not provide an obvious explanation for these discrepancies. These observations offer a cautionary lesson about the strength of inference from complementation and sequence analysis, and commend consideration of more complex phenomena than usually contemplated in Mtb, such as epigenetic control.

Simultaneous functions of the installed DAS/DAK formaldehyde-assimilation pathway and the original formaldehyde metabolic pathways enhance the ability of transgenic geranium to purify gaseous formaldehyde polluted environment.

The overexpression of dihydroxyacetone synthase (DAS) and dihydroxyacetone kinase (DAK) from methylotrophic yeasts in chloroplasts created a photosynthetic formaldehyde (HCHO)-assimilation pathway (DAS/DAK pathway) in transgenic tobacco. Geranium has abilities to absorb and metabolize HCHO. Results of this study showed that the installed DAS/DAK pathway functioning in chloroplasts greatly enhanced the role of the Calvin cycle in transgenic geranium under high concentrations of gaseous HCHO stress. Consequently, the yield of sugars from HCHO-assimilation increased approximately 6-fold in transgenic geranium leaves, and concomitantly, the role of three original HCHO metabolic pathways reduced, leading to a significant decrease in formic acid, citrate and glycine production from HCHO metabolism. Although the role of three metabolic pathways reduced in transgenic plants under high concentrations of gaseous HCHO stress, the installed DAS/DAK pathway could still function together with the original HCHO metabolic pathways. Consequently, the gaseous HCHO-resistance of transgenic plants was significantly improved, and the generation of H2O2 in the transgenic geranium leaves was significantly less than that in the wild type (WT) leaves. Under environmental-polluted gaseous HCHO stress for a long duration, the stomata conductance of transgenic plants remained approximately 2-fold higher than that of the WT, thereby increasing its ability to purify gaseous HCHO polluted environment.

Genome-wide identification, domain architectures and phylogenetic analysis provide new insights into the early evolution of shikimate pathway in prokaryotes.

Despite intense scrutiny from researchers in the fields of biochemistry and metabolism, our understanding of the evolutionary history of the key anabolic shikimate pathway remains limited. To shed light on the early evolutionary events leading to the assembly of the pathway, we investigated the distributions, domain architectures and phylogenies of component enzymes using a bioinformatic procedure based on Hidden Markov Model profiles. The aro genes for the canonical shikimate pathway had most wider distribution in prokaryotes; and the variant pathway coordinated by 2-amino-3,7-dideoxy-D-threo-hept-6-ulosonic acid (ADH) synthase and type II 3-dehydroquinate (DHQ) synthase could be identified in most of archaeal species. In addition, the ancient bidirectional horizontal gene transfer events had happened between two prokaryotic domains: Bacteria and Archaea. Besides 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase, the phylogenetically distinct subfamilies of 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase and chorismate synthase had ever emerged in the evolutionary history of shikimate pathway. These findings provide new insight into the early evolution of the shikimate pathway and advance our understanding of the evolution of metabolic pathways.

A dual conformation of the post-decarboxylation intermediate is associated with distinct enzyme states in mycobacterial KGD (α-ketoglutarate decarboxylase).

α-Ketoacid dehydrogenases are large multi-enzyme machineries that orchestrate the oxidative decarboxylation of α-ketoacids with the concomitant production of acyl-CoA and NADH. The first reaction, catalysed by α-ketoacid decarboxylases (E1 enzymes), needs a thiamine diphosphate cofactor and represents the overall rate-limiting step. Although the catalytic cycles of E1 from the pyruvate dehydrogenase (E1p) and branched-chain α-ketoacid dehydrogenase (E1b) complexes have been elucidated, little structural information is available on E1o, the first component of the α-ketoglutarate dehydrogenase complex, despite the central role of this complex at the branching point between the TCA (tricarboxylic acid) cycle and glutamate metabolism. In the present study, we provide structural evidence that MsKGD, the E1o (α-ketoglutarate decarboxylase) from Mycobacterium smegmatis, shows two conformations of the post-decarboxylation intermediate, each one associated with a distinct enzyme state. We also provide an overall picture of the catalytic cycle, reconstructed by either crystallographic snapshots or modelling. The results of the present study show that the conformational change leading the enzyme from the initial (early) to the late state, although not required for decarboxylation, plays an essential role in catalysis and possibly in the regulation of mycobacterial E1o.

Differentiation of Bacillus anthracis, B. cereus, and B. thuringiensis on the basis of the csaB gene reflects host source.

csaB gene analysis clustered 198 strains of Bacillus anthracis, Bacillus cereus, and Bacillus thuringiensis into two groups related to mammalian and insect hosts, respectively. Mammal-related group I strains also have more S-layer homology (SLH) protein genes than group II strains. This indicates that csaB-based differentiation reflects selective pressure from animal hosts.

The fission yeast Pvg1p has galactose-specific pyruvyltransferase activity.

N-Glycan from the fission yeast Schizosaccharomyces pombe contains outer-chain pyruvic acid 4,6-ketal-linked galactose (PvGal). Here, we characterized a putative S. pombe pyruvyltransferase, Pvg1p, reported to be essential for biosynthesis of PvGal. When p-nitrophenyl-ß-Gal (pNP-ß-Gal) was used as a substrate, the structure of the recombinant Pvg1p product was determined to be pNP-PvGal by one- and two-dimensional NMR spectroscopy. The recombinant Pvg1p transferred pyruvyl residues from phosphoenolpyruvate specifically to ß-linked galactose.

Molecular characterization of two genes with high similarity to the dihydroxyacetone synthase gene in the methylotrophic yeast Pichia methanolica.

The methylotrophic yeast Pichia methanolica possesses two genes, PmDAS1 and PmDLP1, whose amino acid sequences show high similarity to dihydroxyacetone synthase (DAS), the formaldehyde-fixing enzyme for methanol metabolism within the peroxisome. The PmDAS1 and PmDLP1 genes encode 709 and 707 amino acid residues respectively, and PmDas1p contains a type-1 peroxisomal targeting signal (PTS1), while PmDlp1p does not. Upon phylogenetic analysis, PmDas1p fit into the DAS group with other DASs, while PmDlp1p was grouped with the DAS-like proteins (DLP) of non-methylotrophic yeasts and fungi, a branch of the phylogenetic tree independent of the DAS and transketolase (TK) groups. While expression of PmDAS1 restored the methylotrophic growth of the Candida boidinii das1Delta strain, the PmDLP1 and PmDAS1-DeltaPTS1 genes did not. Taken together, these results indicate that PmDAS1 encodes a functional DAS and has an indispensable role in methanol metabolism, and that PmDlp1p share a common, as yet uncharacterized function in P. methanolica as well as in non-methylotrophic yeasts and fungi.

Trm2p-dependent derepression is essential for methanol-specific gene activation in the methylotrophic yeast Candida boidinii.

We identified a gene, designated TRM2, responsible for methanol-inducible gene expression in the methylotrophic yeast Candida boidinii. The encoded protein Trm2p contains two C(2)H(2)-type zinc finger motifs near the N terminus and shows high similarity to Saccharomyces cerevisiae Adr1p and Pichia pastoris Mxr1p. A C. boidinii gene-disrupted strain (trm2Delta) could not grow on methanol or oleate, but could grow on glucose or ethanol. Trm2p was necessary for the activation of five methanol-inducible promoters tested. Trm2p was localized to the nucleus during growth on nonfermentable carbon sources, but to the cytosol during growth on glucose. A chromatin immunoprecipitation assay revealed that Trm2p specifically bound to the promoters of the alcohol oxidase gene (AOD1) and the dihydroxyacetone synthase gene in cells grown on methanol or oleate, but did not bind to these promoters in cells grown on glucose. The derepressed level of expression of AOD1, which was observed in the trm1Delta strain (the TRM1 gene encodes a transcription factor responsible for methanol-specific gene activation), was decreased in the trm1Deltatrm2Delta strain to a level similar to that observed in the trm2Delta strain. These results suggest that Trm2p-dependent derepression is essential for the Trm1p-dependent methanol-specific gene activation in C. boidinii.

Identification of Mxr1p-binding sites in the promoters of genes encoding dihydroxyacetone synthase and peroxin 8 of the methylotrophic yeast Pichia pastoris.

Expression of genes involved in methanol metabolism of Pichia pastoris is regulated by Mxr1p, a zinc finger transcription factor. In this study, we studied the target gene specificity of Mxr1p by examining its ability to bind to promoters of genes encoding dihydroxyacetone synthase (DHAS) and peroxin 8 (PEX8), since methanol-inducible expression of these genes is abrogated in mxr1-null mutant strains of P. pastoris. Different regions of DHAS and PEX8 promoter were isolated from P. pastoris genomic DNA and their ability to bind to a recombinant Mxr1p protein containing the N-terminal 150 amino acids, including the zinc finger DNA-binding domain, was examined. These studies reveal that Mxr1p specifically binds to promoter regions containing multiple 5'-CYCC-3' sequences, although all DNA sequences containing the 5'-CYCC-3' motif do not qualify as Mxr1p-binding sites. Key DNA-binding determinants are present outside 5'-CYCC-3' motif and Mxr1p preferably binds to DNA sequences containing 5'-CYCCNY-3' than those containing 5'-CYCCNR-3' sequences. This study provides new insights into the molecular determinants of target gene specificity of Mxr1p, and the methodology described here can be used for mapping Mxr1p-binding sites in other methanol-inducible promoters of P. pastoris.

Evaluation of substituted triazol-1-yl-pyrimidines as inhibitors of Bacillus anthracis acetohydroxyacid synthase.

Acetohydroxyacid synthase (AHAS), a potential target for antimicrobial agents, catalyzes the first common step in the biosynthesis of the branched-chain amino acids. The genes of both catalytic and regulatory subunits of AHAS from Bacillus anthracis (Bantx), a causative agent of anthrax, were cloned, overexpressed in Escherichia coli, and purified to homogeneity. To develop novel anti-anthracis drugs that inhibit AHAS, a chemical library was screened, and four chemicals, AVS2087, AVS2093, AVS2387, and AVS2236, were identified as potent inhibitors of catalytic subunit with IC(50) values of 1.0 +/- 0.02, 1.0 +/- 0.04, 2.1 +/- 0.12, and 2.0 +/- 0.08 microM, respectively. Further, these four chemicals also showed strong inhibition against reconstituted AHAS with IC(50) values of 0.05 +/- 0.002, 0.153 +/- 0.004, 1.30 +/- 0.10, and 1.29 +/- 0.40 microM, respectively. The basic scaffold of the AVS group consists of 1-pyrimidine-2-yl-1H-[1,2,4]triazole-3-sulfonamide. The potent inhibitor, AVS2093 showed the lowest binding energy, -8.52 kcal/mol and formed a single hydrogen bond with a distance of 1.973 A. As the need for novel antibiotic classes to combat bacterial drug resistance increases, the screening of new compounds that act against Bantx-AHAS shows that AHAS is a good target for new anti-anthracis drugs.

Cloning, characterization and expression of a gene encoding dihydroxyacetone synthase in Mycobacterium sp. strain JC1 DSM 3803.

Dihydroxyacetone synthase (DHAS) is a key enzyme involved in the assimilation of methanol in Mycobacterium sp. strain JC1 DSM 3803. The structural gene encoding DHAS in Mycobacterium sp. strain JC1 was cloned using random-primed probes synthesized after PCR with synthetic primers based on the amino acid sequences conserved in two yeast DHASs and several transketolases. The cloned gene, dasS, had an ORF of 2193 nt, encoding a protein with a calculated molecular mass of 78,197 Da. The deduced amino acid sequence of dasS contained an internal sequence of Mycobacterium sp. strain JC1 DHAS and exhibited 29.2 and 27.3 % identity with those of Candida boidinii and Hansenula polymorpha enzymes, respectively. Escherichia coli transformed with the cloned gene produced a novel protein with a molecular mass of approximately 78 kDa, which cross-reacted with anti-DHAS antiserum and exhibited DHAS activity. Primer-extension analysis revealed that the transcriptional start site of the gene was the nucleotide A located 31 bp upstream from the dasS start codon. RT-PCR showed that dasS was transcribed as a monocistronic message. Northern hybridization and beta-galactosidase assay with the putative promoter region of dasS revealed that the gene was transcribed only in cells growing on methanol. The expression of dasS in Mycobacterium sp. strain JC1 was free from catabolite repression.

The pentose phosphate pathway in Trypanosoma cruzi: a potential target for the chemotherapy of Chagas disease.

Trypanosoma cruzi is highly sensitive to oxidative stress caused by reactive oxygen species. Trypanothione, the parasite's major protection against oxidative stress, is kept reduced by trypanothione reductase, using NADPH; the major source of the reduced coenzyme seems to be the pentose phosphate pathway. Its seven enzymes are present in the four major stages in the parasite's biological cycle; we have cloned and expressed them in Escherichia coli as active proteins. Glucose 6-phosphate dehydrogenase, which controls glucose flux through the pathway by its response to the NADP/NADPH ratio, is encoded by a number of genes per haploid genome, and is induced up to 46-fold by hydrogen peroxide in metacyclic trypomastigotes. The genes encoding 6-phosphogluconolactonase, 6-phosphogluconate dehydrogenase, transaldolase and transketolase are present in the CL Brener clone as a single copy per haploid genome. 6-phosphogluconate dehydrogenase is very unstable, but was stabilized introducing two salt bridges by site-directed mutagenesis. Ribose-5-phosphate isomerase belongs to Type B; genes encoding Type A enzymes, present in mammals, are absent. Ribulose-5-phosphate epimerase is encoded by two genes. The enzymes of the pathway have a major cytosolic component, although several of them have a secondary glycosomal localization, and also minor localizations in other organelles.

The pentose phosphate pathway in Trypanosoma cruzi: a potential target for the chemotherapy of Chagas disease

Trypanosoma cruzi is highly sensitive to oxidative stress caused by reactive oxygen species. Trypanothione, the parasite's major protection against oxidative stress, is kept reduced by trypanothione reductase, using NADPH; the major source of the reduced coenzyme seems to be the pentose phosphate pathway. Its seven enzymes are present in the four major stages in the parasite's biological cycle; we have cloned and expressed them in Escherichia coli as active proteins. Glucose 6-phosphate dehydrogenase, which controls glucose flux through the pathway by its response to the NADP/NADPH ratio, is encoded by a number of genes per haploid genome, and is induced up to 46-fold by hydrogen peroxide in metacyclic trypomastigotes. The genes encoding 6-phosphogluconolactonase, 6-phosphogluconate dehydrogenase, transaldolase and transketolase are present in the CL Brener clone as a single copy per haploid genome. 6-phosphogluconate dehydrogenase is very unstable, but was stabilized introducing two salt bridges by site-directed mutagenesis. Ribose-5-phosphate isomerase belongs to Type B; genes encoding Type A enzymes, present in mammals, are absent. Ribulose-5-phosphate epimerase is encoded by two genes. The enzymes of the pathway have a major cytosolic component, although several of them have a secondary glycosomal localization, and also minor localizations in other organelles.

Trypanosoma cruzi é altamente sensível ao estresse oxidativo causado por espécies reativas do oxigênio. Tripanotiona, o principal protetor do parasita contra o estresse oxidativo, é mantido reduzido pela tripanotiona redutase, pela presença deNADPH; a principal fonte da coenzima reduzida parece ser a via da pentose fosfato. As sete enzimas dessa via estão presentes nos quatro principais estágios do ciclo biológico do parasita; nós clonamos e expressamos as enzimas em Escherichia coli como proteínas ativas. Glucose 6-fosfato desidrogenase, que controla o fluxo da glucose da via em resposta à relação NADP/NADPH, é codificada por um número de genes por genoma haplóide e é induzida até 46-vezes por peróxido de hidrogênio em trypomastigotas metacíclicos. Os genes que codificam 6-fosfogluconolactonase, 6-fosfogluconato desidrogenase, transaldolase e transcetolase estão presentes no clone CL Brener como cópia única por genoma haplóide. 6-fosfogluconato desidrogenase é muito instável, mas foi estabilizada introduzindo duas pontes salinas por mutagênese sítio-dirigida. A Ribose-5-fosfato isomerase pertence ao Tipo B; genes que codificam enzimas Tipo A, presentes em mamíferos estão ausentes. A Ribulose-5-fosfato epimerase é codificada por dois genes. As enzimas da via têm um componente citosólico principal, embora várias delas tenham uma localização glicosomal secundária e também, localizações em menor número em outras organelas.

The final acylation step in taxol biosynthesis: cloning of the taxoid C13-side-chain N-benzoyltransferase from Taxus.

The formation of several acyl groups and an amide group of Taxol is catalyzed by regioselective CoA thioester-dependent acyltransferases. Several full-length acyltransferase sequences, obtained from a cDNA library constructed from mRNA isolated from Taxus cuspidata cells induced for Taxol production with methyl jasmonate, were individually expressed in Escherichia coli, from which a cDNA clone encoding a 3'-N-debenzoyl- 2'-deoxytaxol N-benzoyltransferase was identified. This recombinant enzyme catalyzes the stereoselective coupling of the surrogate substrate N-debenzoyl-(3'RS)-2'-deoxytaxol with benzoyl-CoA to form predominantly one 3'-epimer of 2'-deoxytaxol. The product 2'-deoxytaxol was confirmed by radio-HPLC,(1)H-NMR, and chemical ionization-MS. This enzymatic reaction constitutes the final acylation in the Taxol biosynthetic pathway. The full-length cDNA coding for the N-benzoyltransferase has an ORF of 1,323 nucleotides and encodes a 441-residue protein with a calculated molecular weight of 49,040. The recombinant enzyme expressed in E. coli has a pH optimum at 8.0, a k(cat) approximately 1.5 +/- 0.3 s(-1) and K(m) values of 0.42 mM and 0.40 mM for the N-deacylated taxoid and benzoyl-CoA, respectively. In addition to improving the production yields of Taxol in genetically engineered host systems, this enzyme provides a means of attaching modified aroyl groups to taxoid precursors for the purpose of improving drug efficacy.

A methylotrophic pathway participates in pectin utilization by Candida boidinii.

The methylotrophic yeast Candida boidinii S2 was found to be able to grow on pectin or polygalacturonate as a carbon source. When cells were grown on 1% (wt/vol) pectin, C. boidinii exhibited induced levels of the pectin-depolymerizing enzymes pectin methylesterase (208 mU/mg of protein), pectin lyase (673 mU/mg), pectate lyase (673 mU/mg), and polygalacturonase (3.45 U/mg) and two methanol-metabolizing peroxisomal enzymes, alcohol oxidase (0.26 U/mg) and dihydroxyacetone synthase (94 mU/mg). The numbers of peroxisomes also increased ca. two- to threefold in cells grown on these pectic compounds (3.34 and 2.76 peroxisomes/cell for cells grown on pectin and polygalacturonate, respectively) compared to the numbers in cells grown on glucose (1.29 peroxisomes/cell). The cell density obtained with pectin increased as the degree of methyl esterification of pectic compounds increased, and it decreased in strains from which genes encoding alcohol oxidase and dihydroxyacetone synthase were deleted and in a peroxisome assembly mutant. Our study showed that methanol metabolism and peroxisome assembly play important roles in the degradation of pectin, especially in the utilization of its methyl ester moieties.