Dimethylallyltryptophan Synthase Research Articles

Clustered genes involved in cyclopiazonic acid production are next to the aflatoxin biosynthesis gene cluster in Aspergillus flavus

Cyclopiazonic acid (CPA), an indole-tetramic acid mycotoxin, is produced by many species of Aspergillus and Penicillium. In addition to CPA Aspergillus flavus produces polyketide-derived carcinogenic aflatoxins. Aflatoxin biosynthesis genes form a gene cluster in a subtelomeric region. Isolates of A. flavus lacking aflatoxin production due to the loss of the entire aflatoxin gene cluster and portions of the subtelomeric region are often unable to produce CPA, which suggests a physical link of genes involved in CPA biosynthesis to the aflatoxin gene cluster. Examining the subtelomeric region in A. flavus isolates of different chemotypes revealed a region possibly associated with CPA production. Disruption of three of the four genes present in this region predicted to encode a monoamine oxidase, a dimethylallyl tryptophan synthase, and a hybrid polyketide non-ribosomal peptide synthase abolished CPA production in an aflatoxigenic A. flavus strain. Therefore, some of the CPA biosynthesis genes are organized in a mini-gene cluster that is next to the aflatoxin gene cluster in A. flavus.

The GC and window-averaged DNA curvature profile of secondary metabolite gene cluster in Aspergillus fumigatus genome

An immense variety of complex secondary metabolites is produced by filamentous fungi including Aspergillus fumigatus, a main inducer of invasive aspergillosis. The identification of fungal secondary metabolite gene cluster is essential for the characterization of fungal secondary metabolism in terms of genetics and biochemistry through recombinant technologies such as gene disruption and cloning. Most of the prediction methods for secondary metabolite gene cluster severely depend on homology searches. However, homology-based approach has intrinsic limitation to unknown or novel gene cluster. We analyzed the GC and window-averaged DNA curvature profile of 26 secondary metabolite gene clusters in the A. fumigatus genome to find out potential conserved features of secondary metabolite gene cluster. Fifteen secondary metabolite gene clusters showed a conserved pattern in window-averaged DNA curvature profile, that is, the DNA regions including secondary metabolic signature genes such as polyketide synthase, nonribosomal peptide synthase, and/or dimethylallyl tryptophan synthase consisted of window-averaged DNA curvature values lower than 0.18 and these DNA regions were at least 20 kb. Forty percent of secondary metabolite gene clusters with this conserved pattern were related to severe regulation by a transcription factor, LaeA. Our result could be used for identification of other fungal secondary metabolite gene clusters, especially for secondary metabolite gene cluster that is severely regulated by LaeA or other proteins with similar function to LaeA.

A 7-dimethylallyltryptophan synthase from Aspergillus fumigatus: overproduction, purification and biochemical characterization

A putative prenyltransferase gene, Afu3g12930, was identified in the genome sequence of Aspergillus fumigatus. EAL92290, encoded by Afu3g12930, consists of 472 aa, with a molecular mass of about 53 kDa. The coding sequence of Afu3g12930 was cloned in pQE60, and overexpressed in Escherichia coli. The soluble His(6)-fusion protein was purified to apparent homogeneity, and characterized biochemically. The enzyme was found to catalyse the prenylation of Trp at the C-7 position of the indole moiety, in the presence of dimethylallyl diphosphate (DMAPP); therefore, it functions as a 7-dimethylallyltryptophan synthase (7-DMATS). The structure of the enzymic product was elucidated by NMR and MS analysis. K(m) values were 67 microM for DMAPP, and 137 microM for l-Trp. Geranyl diphosphate was not accepted as prenyl donor, while Trp-containing dipeptides were found to be aromatic substrates of 7-DMATS. 7-DMATS did not need divalent metal ions for its enzymic reaction, although Ca(2+) enhanced the reaction velocity slightly. The enzyme is the second dimethylallyltryptophan synthase identified in A. fumigatus. Interestingly, it shares a sequence identity of only 31 % at the amino acid level with another known dimethylallyltryptophan synthase, FgaPT2, from the same fungus; FgaPT2 prenylates l-Trp at the C-4 position of the indole ring. Afu3g12930 belongs to a putative biosynthetic gene cluster consisting of eight genes. Orthologous clusters were also identified in the genome sequences of Neosartorya fischeri and Aspergillus terreus. The putative roles of the genes in the cluster are discussed.

Towards the elimination of ergot alkaloid biosynthesis genes in Neotyphodium Coenophialum

Neotyphodium coenophialum strain e19 from tall fescue cv. Kentucky 31 carries dmaW1 and dmaW2, two gene homologues that encode dimethylallyltryptophan synthase, the enzyme for the first step in ergot-alkaloid biosynthesis. In our effort to disrupt both homologues and ultimately obtain marker-free mutants, we are using a marker-exchange strategy employing the Cre/ loxP site-specific recombination system. Of 1522 transformants obtained and screened, three were likely dmaW2 disruptants because they gave no PCR product from the wild-type locus, but yielded the larger PCR fragment from the disruption construct. The putative dmaW2-knockouts were also transformed with pKAES186, a plasmid with a cassette containing the cre and ble genes in between loxP sequences. The transformants obtained were screened for the presence of hph, cre and ble genes. The preliminary results indicate a loop-out of the hph gene. The transformants inoculated into endophyte-free tall fescue preserved their compatibility with the plant. The fungus grown from these plants will be further analysed for the presence of hph, cre and ble genes. Keywords: Cre/LoxP, dimethylallyltryptophan synthase, dmaW, Epichloë, ergot alkaloids, Festuca arundinacea, gene knockouts, Lolium arundinaceum, Neotyphodium coenophialum, tall fescue

Post-Genome Research on the Biosynthesis of Ergot Alkaloids

Genome sequencing provides new opportunities and challenges for identifying genes for the biosynthesis of secondary metabolites. A putative biosynthetic gene cluster of fumigaclavine C, an ergot alkaloid of the clavine type, was identified in the genome sequence of ASPERGILLUS FUMIGATUS by a bioinformatic approach. This cluster spans 22 kb of genomic DNA and comprises at least 11 open reading frames (ORFs). Seven of them are orthologous to genes from the biosynthetic gene cluster of ergot alkaloids in CLAVICEPS PURPUREA. Experimental evidence of the identified cluster was provided by heterologous expression and biochemical characterization of two ORFs, FgaPT1 and FgaPT2, in the cluster of A. FUMIGATUS, which show remarkable similarities to dimethylallyltryptophan synthase from C. PURPUREA and function as prenyltransferases. FgaPT2 converts L-tryptophan to dimethylallyltryptophan and thereby catalyzes the first step of ergot alkaloid biosynthesis, whilst FgaPT1 catalyzes the last step of the fumigaclavine C biosynthesis, i. e., the prenylation of fumigaclavine A at C-2 position of the indole nucleus. In addition to information obtained from the gene cluster of ergot alkaloids from C. PURPUREA, the identification of the biosynthetic gene cluster of fumigaclavine C in A. FUMIGATUS opens an alternative way to study the biosynthesis of ergot alkaloids in fungi.

The Crystal Structure of (S)-3-O-Geranylgeranylglyceryl Phosphate Synthase Reveals an Ancient Fold for an Ancient Enzyme

We report crystal structures of the citrate and sn-glycerol-1-phosphate (G1P) complexes of (S)-3-O-geranylgeranylglyceryl phosphate synthase from Archaeoglobus fulgidus (AfGGGPS) at 1.55 and 2.0 A resolution, respectively. AfGGGPS is an enzyme that performs the committed step in archaeal lipid biosynthesis, and it presents the first triose phosphate isomerase (TIM)-barrel structure with a prenyltransferase function. Our studies provide insight into the catalytic mechanism of AfGGGPS and demonstrate how it selects for the sn-G1P isomer. The replacement of "Helix 3" by a "strand" in AfGGGPS, a novel modification to the canonical TIM-barrel fold, suggests a model of enzyme adaptation that involves a "greasy slide" and a "swinging door." We propose functions for the homologous PcrB proteins, which are conserved in a subset of pathogenic bacteria, as either prenyltransferases or being involved in lipoteichoic acid biosynthesis. Sequence and structural comparisons lead us to postulate an early evolutionary history for AfGGGPS, which may highlight its role in the emergence of Archaea.

Overproduction, purification and characterization of FtmPT1, a brevianamide F prenyltransferase from Aspergillus fumigatus

A putative prenyltransferase gene, ftmPT1, was identified in the genome sequence of Aspergillus fumigatus. ftmPT1 was cloned and expressed in Escherichia coli, and the protein FtmPT1 was purified to near homogeneity and characterized biochemically. This enzyme was found to catalyse the prenylation of cyclo-L-trp-L-Pro (brevianamide F) at the C-2 position of the indole nucleus. FtmPT1 is a soluble monomeric protein, which does not contain the usual prenyl diphosphate binding site (N/D)DXXD found in most prenyltransferases, and which does not require divalent metal ions for its enzymic activity. K(m) values for brevianamide F and dimethylallyl diphosphate were determined as 55 and 74 microM, respectively. The turnover number was 5.57 s(-1). FtmPT1 showed a high substrate specificity towards dimethylallyl diphosphate, but accepted different tryptophan-containing cyclic dipeptides. Together with dimethylallyltryptophan synthase of ergot alkaloid biosynthesis, FtmPT1 belongs to a new group of prenyltransferases with aromatic substrates.

Overproduction, purification and characterization of FgaPT2, a dimethylallyltryptophan synthase from Aspergillus fumigatus

A putative dimethylallyltryptophan synthase gene, fgaPT2, was identified in the genome sequence of Aspergillus fumigatus. fgaPT2 was cloned and overexpressed in Saccharomyces cerevisiae. The protein FgaPT2 was purified to near homogeneity and characterized biochemically. This enzyme was found to convert L-tryptophan to 4-dimethylallyltryptophan, a reaction known to be the first step in ergot alkaloid biosynthesis. FgaPT2 is a soluble, dimeric protein with a subunit size of 52 kDa, and contains no putative prenyl diphosphate binding site (N/D)DXXD. Km values for L-tryptophan and dimethylallyl diphosphate (DMAPP) were determined as 8 and 4 microM, respectively. Metal ions, such as Mg2+ and Ca2+, enhance the reaction velocity, but are not essential for the enzymic reaction. FgaPT2 showed a relatively strict substrate specificity for both tryptophan and DMAPP. FgaPT2 is the first enzyme in the biosynthesis of ergot alkaloids to be purified and characterized in homogeneous form after heterologous overproduction.

The determinant step in ergot alkaloid biosynthesis by an endophyte of perennial ryegrass

Many cool-season grasses harbor fungal endophytes in the genus Neotyphodium, which enhance host fitness, but some also produce metabolites—such as ergovaline—believed to cause livestock toxicoses. In Claviceps species the first step in ergot alkaloid biosynthesis is thought to be dimethylallyltryptophan (DMAT) synthase, encoded by dmaW, previously cloned from Claviceps fusiformis. Here we report the cloning and characterization of dmaW from Neotyphodium sp. isolate Lp1, an endophyte of perennial ryegrass ( Lolium perenne). The gene was then disrupted, and the mutant failed to produce any detectable ergovaline or simpler ergot and clavine alkaloids. The disruption was complemented with the C. fusiformis gene, which restored ergovaline production. Thus, the biosynthetic role of DMAT synthase was confirmed, and a mutant was generated for future studies of the ecological and agricultural importance of ergot alkaloids in endophytes of grasses.

The phylogeny and evolution of the genus Claviceps

Phylogenetic trees of 16 Claviceps species were constructed based on alignments of 5.8S rDNA and the adjacent ITS1 and ITS2 spacers. Two highly supported clades were found: (1) C. paspali, C. zizaniae, C. grohii, C. sulcata, C. fusiformis, and C. purpurea; and (2) C. citrina, C. phalaridis, two unidentified Claviceps spp. (isolates PM and SG), C. sorghicola, C. gigantea, C. sorghi, C. africana, C. viridis, and C. pusilla. No relationship was found between the species placement and its morphological markers. The probe from C. purpurea gene cpd1 for dimethylallyl tryptophan synthase, the first enzyme of alkaloid biosynthesis, was hybridized to Pst 1 digested genomes of the above species under non-stringent conditions. Hybridizing DNA was present in all species of clade 1, although the signal of the C. paspali gene was weaker. In clade 2, only C. africana, C. gigantea, and C. pusilla gave weak positive signals. Colorimetric detection found small amounts of alkaloids in cultures of Claviceps sp. SG and PM but despite that, no cpd1 hybridizing bands were found. The occurrence of two major clades of Claviceps and their biogeography suggests, that the genus originates from South America and that the evolution of its species was influenced by comigration with their hosts and with the global climatic changes that influenced spreading of grass subfamilies.

Molecular cloning and genetic analysis of an indole-diterpene gene cluster from Penicillium paxilli.

The indole-diterpene paxilline is a potent tremorgenic mammalian mycotoxin and a known inhibitor of maxi-K ion channels. The gene cluster responsible for paxilline biosynthesis in Penicillium paxilli was identified by mapping four large plasmid-induced chromosome deletions. The cluster is predicted to lie within a 50 kb region of chromosome Va and to contain 17 genes, including a geranylgeranyl pyrophosphate (GGPP) synthase (paxG), two FAD-dependent monooxygenases (paxM and N), two cytochrome P450 monooxygenases (paxP and Q), a dimethylallyltryptophan (DMAT) synthase (paxD) and two possible transcription factors (paxR and paxS), which contain a Zn(II)2Cys6 DNA-binding motif. Targeted replacement of paxG confirmed that it is essential for paxilline biosynthesis but dispensable for growth. The GGPP for primary metabolism is predicted to be provided by a second GGPP synthase (ggs1) that was cloned, sequenced and mapped to chromosome IV. Semi-quantitative reverse transcriptase-polymerase chain reaction analysis demonstrated that the expression of paxG, paxM and paxP in submerged liquid cultures of P. paxilli increased dramatically with the onset of paxilline biosynthesis. In contrast, the expression of beta-tubulin (tub2) and ggs1 was not induced. This is the first description of the molecular cloning and genetic analysis of an indole-diterpene gene cluster.

Evidence for an ergot alkaloid gene cluster in Claviceps purpurea.

A gene (cpd1) coding for the dimethylallyltryptophan synthase (DMATS) that catalyzes the first specific step in the biosynthesis of ergot alkaloids, was cloned from a strain of Claviceps purpurea that produces alkaloids in axenic culture. The derived gene product (CPD1) shows only 70% similarity to the corresponding gene previously isolated from Claviceps strain ATCC 26245, which is likely to be an isolate of C. fusiformis. Therefore, the related cpd1 most probably represents the first C. purpurea gene coding for an enzymatic step of the alkaloid biosynthetic pathway to be cloned. Analysis of the 3'-flanking region of cpd1 revealed a second, closely linked ergot alkaloid biosynthetic gene named cpps1, which codes for a 356-kDa polypeptide showing significant similarity to fungal modular peptide synthetases. The protein contains three amino acid-activating modules, and in the second module a sequence is found which matches that of an internal peptide (17 amino acids in length) obtained from a tryptic digest of lysergyl peptide synthetase 1 (LPS1) of C. purpurea, thus confirming that cpps1 encodes LPS1. LPS1 activates the three amino acids of the peptide portion of ergot peptide alkaloids during D-lysergyl peptide assembly. Chromosome walking revealed the presence of additional genes upstream of cpd1 which are probably also involved in ergot alkaloid biosynthesis: cpox1 probably codes for an FAD-dependent oxidoreductase (which could represent the chanoclavine cyclase), and a second putative oxidoreductase gene, cpox2, is closely linked to it in inverse orientation. RT-PCR experiments confirm that all four genes are expressed under conditions of peptide alkaloid biosynthesis. These results strongly suggest that at least some genes of ergot alkaloid biosynthesis in C. purpurea are clustered, opening the way for a detailed molecular genetic analysis of the pathway.

Identification of genes induced in alkaloid-producing cultures of Claviceps sp.

In order to identify genes which are expressed during alkaloid synthesis in an axenic culture of Claviceps sp. (strain ATCC 26245), a cDNA library from a producing culture was differentially screened with cDNA from producing (cDNA+) and non-producing (cDNA-) cultures, respectively. Altogether, ten cDNA clones were obtained, the alkaloid-synthesis-correlated expression of which was confirmed by Northern analyses. Evaluation of their nucleotide and derived amino-acid sequences identified one gene unequivocally, coding for dimethylallyltryptophan-synthase (DMAT-S), the initial enzyme of the specific alkaloid pathway. For two other genes significant homologies to known fungal genes were detected: one clone showed homology to the Neurospora crassa ccg1 gene, coding for a clock-regulated putative general stress protein; seven cDNA clones, derived from the same gene, which is highly expressed under these conditions, contained typical hydrophobin domains and long stretches of asparagine/glycine repeats (like QID3 from Trichoderma harzianum), thus probably representing a cell-wall constituent. These data show that this is not only a successful approach to clone genes specific for the alkaloid-pathway of C. purpurea, but also of genes which might be involved in the differentiation of sclerotial hyphae, the prerequisite for alkaloid synthesis.

The Claviceps purpurea Gene Encoding Dimethylallyltryptophan Synthase, the Committed Step for Ergot Alkaloid Biosynthesis

The first pathway-specific step of ergot alkaloid biosynthesis in the fungus, Claviceps purpurea, is catalyzed by the prenyltransferase, 4-(γ,γ-dimethylallyl)tryptophan synthase. Partial sequence information was obtained for the purified enzyme and a degenerate oligonucleotide mixture was used to identify and amplify segments of the gene, dmaW. The complete gene and near-full-length cDNA were cloned and sequenced. The cDNA was cloned in a yeast expression vector in sense and antisense orientations relative to the inducible GAL1 promoter. Extracts of yeast transformants with the sense constructs, but not antisense constructs or cloning vector, catalyzed production of 4-(γ,γ-dimethylallyl)tryptophan. The sequence of dmaW and its cDNA indicated that it encoded a 455 amino acid polypeptide with a predicted molecular mass of 51,824 Da and a putative prenyl diphosphate binding motif.

Dimethylallyltryptophan synthase. An enzyme-catalyzed electrophilic aromatic substitution

Dimethylallyltryptophan (DMAT) synthase catalyzes the alkylation of L-tryptophan at C(4) by dimethylallyl diphosphate (DMAPP) in the first pathway-specific step in the biosynthesis of ergot alkaloids. The mechanism of the reaction was studied with analogs of both substrates. Five 7-substituted derivatives of N-acetyltryptophan (2, Z=OCH 3 , CH 3 , F, CF 3 , and NO 2 ) were synthesized. The L enantiomers of the free amino acids were obtained by selective hydrolysis of the racemate using aminoacylase from Aspergillus

Purification and characterization of dimethylallyl tryptophan synthase from Claviceps purpurea

Dimethylallyl tryptophan synthase (DMAT synthase) catalyzes the alkylation of l-tryptophan by dimethylallyl diphosphate to form 4-(γ,γ-dimethylallyl)- l-tryptophan. The enzyme from mycelia of Claviceps purpurea was purified approximately 125-fold to apparent homogeneity by chromatography on n-butyl Sepharose, Q Sepharose, phenyl Sepharose, and Protein Pak as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Analysis by gel filtration chromatography and SDS-PAGE indicated that DMAT synthase is an α 2 dimer with a molecular mass of 105 kDa. The purified enzyme was active in metal-free buffer containing EDTA. However, activity was enhanced upon addition of divalent calcium or magnesium ions to the buffer. Values for K M and V max were determined in the metal-free EDTA buffer ( K M DMAPP, 14 μM; K M L-tryptophan, 40 μM; V max, 215 nmol min −1 mg −1), 4 m m CaCl 2 ( K M DMAPP, 8.0 μM; K M L-truptophan, 17 μM; V max, 504 nmol min −1 mg −1), and 4 m m MgCl 2 ( K M DMAPP, 8.0 μM; K M L-tryptophan, 12 μM; V max, 455 nmol min −1 mg −1). The product was isolated and characterized by 1H NMR, uv, and FAB mass spectrometry.