The Aspergillus niger faeB gene encodes a second feruloyl esterase involved in pectin and xylan degradation and is specifically induced in the presence of aromatic compounds

Gene overexpression and biochemical characterization of the biotechnologically relevant chlorogenic acid hydrolase from Aspergillus niger

The full-length gene that encodes the chlorogenic acid hydrolase from Aspergillus niger CIRM BRFM 131 was cloned by PCR based on the genome of the strain A. niger CBS 513.88. The complete gene consists of 1,715 bp and codes for a deduced protein of 512 amino acids with a molecular mass of 55,264 Da and an acidic pI of 4.6. The gene was successfully cloned and overexpressed in A. niger to yield 1.25 g liter(-1), i.e., 330-fold higher than the production of wild-type strain A. niger CIRM BRFM131. The histidine-tagged recombinant ChlE protein was purified to homogeneity via a single chromatography step, and its main biochemical properties were characterized. The molecular size of the protein checked by mass spectroscopy was 74,553 Da, suggesting the presence of glycosylation. ChlE is assembled in a tetrameric form with several acidic isoforms with pIs of around 4.55 and 5.2. Other characteristics, such as optimal pH and temperature, were found to be similar to those determined for the previously characterized chlorogenic acid hydrolase of A. niger CIRM BRFM 131. However, there was a significant temperature stability difference in favor of the recombinant protein. ChlE exhibits a catalytic efficiency of 12.5 x 10(6) M(-1) s(-1) toward chlorogenic acid (CGA), and its ability to release caffeic acid from CGA present in agricultural by-products such as apple marc and coffee pulp was clearly demonstrated, confirming the high potential of this enzyme.

Association of tannase-producing Staphylococcus lugdunensis with colon cancer and characterization of a novel tannase gene

BACKGROUND

The relationship between Streptococcus (St.) bovis endocarditis and colon cancer is well known. In St. bovis, the biotype I strain (formerly, St. gallolyticus) produces tannase that degrades tannins. The aim of this study was to investigate the association of tannase-producing bacteria with colon cancer, and to identify the major tannase-producing bacteria and the gene involved.

METHODS

Tannase-producing bacteria were isolated in tannic acid-treated selective agar medium from feces and rectal swabs of 357 patients who underwent colon endoscopy from 1999 to 2004.

RESULTS

Tannase-producing bacteria were isolated more frequently from the colon cancer group (24.3%) than from the adenoma or normal groups (14.4%; P < 0.05). S. gallolyticus, Staphylococcus (S.) lugdunensis, Lactobacillus (L.) plantarum, and L. pentosus were all identified as tannase-producing bacteria. Of these, S. lugdunensis was significantly isolated from the advanced-stage cancer group (22.2%; P < 0.001) more than from the early-stage cancer (8.6%) or adenoma (4.9%) groups. The gene (tanA) for tannase in S. lugdunensis was cloned and sequenced. The tanA gene was associated with all S. lugdunensis but not with other bacteria by Southern blotting and polymerase chain reaction.

CONCLUSIONS

Tannase-producing S. lugdunensis is associated with advanced-stage colon cancer, and the tanA gene is a useful marker for the detection of S. lugdunensis.

Phylogenetic analysis of the Aspergillus niger aggregate in relation to feruloyl esterase activity

Species of the Aspergillus niger aggregate are known to produce feruloyl esterases, enzymes involved in the degradation of cell wall polymers. However, species delineation is difficult in these fungi. We combined AFLP analysis with ITS rDNA and beta-tubulin sequencing to characterize the isolates of this aggregate in terms of feruloyl esterase production. A preliminary re-examination of isolates based on comparison of ITS rDNA and beta-tubulin sequences with those of typical taxa deposited in international collections led us to re-identify the isolates as members of the species A. niger, A. foetidus and A. tubingensis. Molecular clustering based on beta-tubulin data and AFLP analysis showed that the strains of A. niger formed a homogenous phylogenetic group distinguished by either zero or type A feruloyl esterase activity, while strains A. foetidus and A. tubingensis exhibited type B feruloyl esterase activity when grown on sugar beet pulp.

Esterification of ferulic acid with polyols using a ferulic acid esterase from Aspergillus niger

Commercially available enzyme preparations were screened for enzymes that have a high ability to catalyze direct ester-synthesis of ferulic acid with glycerol. Only a preparation, Pectinase PL "Amano" produced by Aspergillus niger, feruloylated glycerol under the experimental conditions. The enzyme responsible for the esterification was purified and characterized. This enzyme, called FAE-PL, was found to be quite similar to an A. niger ferulic acid esterase (FAE-III) in terms of molecular mass, pH and temperature optima, substrate specificity on synthetic substrates, and the N-terminal amino acid sequence. FAE-PL highly catalyzed direct esterification of ferulic acid and sinapinic acid with glycerol. FAE-PL could feruloylate monomeric sugars including arabinose, fructose, galactose, glucose, and xylose. We determined the suitable conditions for direct esterification of ferulic acid with glycerol to be as follows: 1% ferulic acid in the presence of 85% glycerol and 5% dimethyl sulfoxide at pH 4.0 and 50 degrees C. Under these conditions, 81% of ferulic acid could be converted to 1-glyceryl ferulate, which was identified by (1)H-NMR. The ability of 1-glyceryl ferulate to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals was higher than that of the anti-oxidant butyl hydroxytoluene.

Construction of engineered bifunctional enzymes and their overproduction in Aspergillus niger for improved enzymatic tools to degrade agricultural by-products

Two chimeric enzymes, FLX and FLXLC, were designed and successfully overproduced in Aspergillus niger. FLX construct is composed of the sequences encoding the feruloyl esterase A (FAEA) fused to the endoxylanase B (XYNB) of A. niger. A C-terminal carbohydrate-binding module (CBM family 1) was grafted to FLX, generating the second hybrid enzyme, FLXLC. Between each partner, a hyperglycosylated linker was included to stabilize the constructs. Hybrid proteins were purified to homogeneity, and molecular masses were estimated to be 72 and 97 kDa for FLX and FLXLC, respectively. Integrity of hybrid enzymes was checked by immunodetection that showed a single form by using antibodies raised against FAEA and polyhistidine tag. Physicochemical properties of each catalytic module of the bifunctional enzymes corresponded to those of the free enzymes. In addition, we verified that FLXLC exhibited an affinity for microcrystalline cellulose (Avicel) with binding parameters corresponding to a Kd of 9.9 x 10(-8) M for the dissociation constant and 0.98 micromol/g Avicel for the binding capacity. Both bifunctional enzymes were investigated for their capacity to release ferulic acid from natural substrates: corn and wheat brans. Compared to free enzymes FAEA and XYNB, a higher synergistic effect was obtained by using FLX and FLXLC for both substrates. Moreover, the release of ferulic acid from corn bran was increased by using FLXLC rather than FLX. This result confirms a positive role of the CBM. In conclusion, these results demonstrated that the fusion of naturally free cell wall hydrolases and an A. niger-derived CBM onto bifunctional enzymes enables the increase of the synergistic effect on the degradation of complex substrates.

Homologous expression of the feruloyl esterase B gene from Aspergillus niger and characterization of the recombinant enzyme

The faeB gene encoding the feruloyl esterase B (FAEB) was isolated from Aspergillus niger BRFM131 genomic DNA. The faeB gene, with additional sequence coding for a C-terminal histidine tag, was inserted into an expression vector under the control of the gpd promoter and trpC terminator and expressed in a protease deficient A. niger strain. Homologous overproduction allows to reach an esterase activity of 18 nkat mL(-1) against MCA as substrate. The improvement factor was 16-fold higher as compared to the production level obtained with non-transformed A. niger strain induced by sugar beet pulp. The corresponding secretion yield was estimated to be around 100 mg L(-1). Recombinant FAEB was purified 14.6-fold to homogeneity from an 8-day-old culture by a single affinity chromatographic step with a recovery of 64%. SDS-PAGE revealed a single band with a molecular mass of 75 kDa, while under non-denatured conditions, native enzyme has a molecular mass of around 150 kDa confirming that the recombinant FAEB is a homodimer. The recombinant and native FAEB have the same characteristics concerning temperature and pH optima, i.e., 50 degrees C and 6, respectively. In addition, the recombinant FAEB was determined to be quite stable up to 50 degrees C for 120 min. Kinetic constants for MCA, MpCA, and chlorogenic acid (5-O-caffeoyl quinic acid) were as follows: Km: 0.13, 0.029, and 0.16 mM and Vmax: 1101, 527.6, and 28.3 nkat mg(-1), respectively. This is the first report on the homologous overproduction of feruloyl esterase B in A. niger.

Purification and characterization of a chlorogenic acid hydrolase from Aspergillus niger catalysing the hydrolysis of chlorogenic acid

Among 15 Aspergillus strains, Aspergillus niger BRFM 131 was selected for its high chlorogenic acid hydrolase activity. The enzyme was purified and characterized with respect to its physico-chemical and kinetic properties. Four chromatographic steps were necessary to purify the protein to homogeneity with a recovery of 2%. Km of the chlorogenic acid hydrolase was estimated to be 10 microM against chlorogenic acid as substrate. Under native conditions, the protein presented a molecular mass of 170 kDa, and SDS-PAGE analysis suggested the presence of two identical 80 kDa subunits. Isoelectric point was 6.0; pH optimum for activity was determined to be 6.0 and temperature optima to be 55 degrees C. The N-terminal sequence did not present any homology with other cinnamoyl ester hydrolases previously described suggesting the purification of a new protein. The chlorogenic acid hydrolase was used successfully for the production of caffeic acid, which possesses strong antioxidant properties, from natural substrates specially rich in chlorogenic acid like apple marc and coffee pulp.

The Crystal Structure of Feruloyl Esterase A from Aspergillus niger Suggests Evolutive Functional Convergence in Feruloyl Esterase Family

As a component of the array of enzymes produced by micro-organisms to deconstruct plant cell walls, feruloyl esterases hydrolyze phenolic groups involved in the cross-linking of arabinoxylan to other polymeric structures. This is important for opening the cell wall structure, making material more accessible to glycosyl hydrolases. Here, we describe the first crystal structure of the non-modular type-A feruloyl esterase from Aspergillus niger (AnFaeA) solved at 2.5A resolution. AnFaeA displays an alpha/beta hydrolase fold similar to that found in fungal lipases and different from that reported for other feruloyl esterases. Crystallographic and site-directed mutagenesis studies allow us to identify the catalytic triad (Ser133-His247-Asp194) that forms the catalytic machinery of this enzyme. The active-site cavity is confined by a lid (residues 68-80), on the analogy of lipases, and by a loop (residues 226-244) that confers plasticity to the substrate-binding site. The lid presents a high ratio of polar residues, which in addition to a unique N-glycosylation site stabilises the lid in an open conformation, conferring the esterase character to this enzyme. A putative model for bound 5,5'-diferulic acid-linked arabinoxylan has been built, pointing to the more relevant residues involved in substrate recognition. Comparison with structurally related lipases reveals that subtle amino acid and conformational changes within a highly conserved protein fold may produce protein variants endowed with new enzymatic properties, while comparison with functionally related proteins points to a functional convergence after evolutionary divergence within the feruloyl esterases family.

The feruloyl esterase system of Talaromyces stipitatus: production of three discrete feruloyl esterases, including a novel enzyme, TsFaeC, with a broad substrate specificity

Several extracellular feruloyl esterases were produced by the mesophilic fungus Talaromyces stipitatus when grown on selective carbon sources in liquid media. Type-A and Type-B feruloyl esterases, as defined by their substrate specificity against methyl hydroxycinnamates, were produced during growth on wheat bran and sugar beet pulp, respectively. In addition, Tal. stipitatus produced a new type of esterase (TsFaeC) during growth on sugar beet pulp with a broader spectrum of activity (Type-C) against the (hydroxy)cinnamate esters than those previously described. All three enzymes were purified and N-terminal amino acid sequences and internal peptide sequences determined. The TsFaeC sequences were used to amplify a gene fragment from Tal. stipitatus genomic DNA. The flanking sequences were identified with the aid of RACE-RTPCR, and a full-length clone constructed. The faeC gene is present as a single copy and contains a single intron. The complete cDNA fragment contains an ORF of 1590bp, faeC, which is predicted to encode a 530 amino acid pre-protein, including a 25-residue signal peptide, and to produce a mature protein of M(R) 55 340Da. There was no evidence for a carbohydrate-binding domain in TsFaeC.

Production and characterization of the Talaromyces stipitatus feruloyl esterase FAEC in Pichia pastoris: identification of the nucleophilic serine

Feruloyl esterases constitute an interesting group of enzymes that have the potential for use over a broad range of applications in the agri-food industries. We report the over-expression and characterization of a novel feruloyl esterase exhibiting broad substrate specificity from Talaromyces stipitatus (FAEC) in Pichia pastoris. Using various gene constructions, we have investigated the use of alternative signal peptides to produce an authentic feruloyl esterase featuring the N-terminal sequence determined for the native enzyme. We demonstrate that additional amino acids at the N-terminus of the FAEC sequence do not influence the catalytic capacity of the enzyme, and that the nature of the signal sequence has a limited effect on the yield of the secreted enzyme, with the T. stipitatus FAEC signal sequence producing 297 mgL(-1), the Neurospora crassa Fae-1 260 mgL(-1), and the Saccharomyces cerevisiae alpha-factor secretion signal 214 mgL(-1). Mature FAEC contains two internal peptide sequences that correspond with the consensus motif G-X-S-X-G that contains the catalytic serine nucleophile, which is conserved in the esterase enzyme superfamily. The serine residues at the center of these peptide motifs have been independently mutated and the corresponding enzymes have been over-expressed in P. pastoris to identify the candidate nucleophilic residue responsible for catalyzing the enzymatic reaction. Purified recombinant FAEC containing S465A retained the esterase activity and appeared unaffected by the amino acid modification. In contrast, FAEC activity containing S166A was below the HPLC detection limit, suggesting that serine 166 constitutes the nucleophile.

A non-modular type B feruloyl esterase from Neurospora crassa exhibits concentration-dependent substrate inhibition

Feruloyl esterases, a subclass of the carboxylic acid esterases (EC 3.1.1.1), are able to hydrolyse the ester bond between the hydroxycinnamic acids and sugars present in the plant cell wall. The enzymes have been classified as type A or type B, based on their substrate specificity for aromatic moieties. We show that Neurospora crassa has the ability to produce multiple ferulic acid esterase activities depending upon the length of fermentation with either sugar beet pulp or wheat bran substrates. A gene identified on the basis of its expression on sugar beet pulp has been cloned and overexpressed in Pichia pastoris. The gene encodes a single-domain ferulic acid esterase, which represents the first report of a non-modular type B enzyme (fae-1 gene; GenBank accession no. AJ293029). The purified recombinant protein has been shown to exhibit concentration-dependent substrate inhibition (K(m) 0.048 mM, K (i) 2.5 mM and V(max) 8.2 units/mg against methyl 3,4-dihydroxycinnamate). The kinetic behaviour of the non-modular enzyme is discussed in terms of the diversity in the roles of the feruloyl esterases in the mobilization of plant cell wall materials and their respective modes of action.

Genes for chlorogenate and hydroxycinnamate catabolism (hca) are linked to functionally related genes in the dca-pca-qui-pob-hca chromosomal cluster of Acinetobacter sp. strain ADP1

Hydroxycinnamates are ubiquitous in the environment because of their contributions to the structure and defense mechanisms of plants. Additional plant products, many of which are formed in response to stress, support the growth of Acinetobacter sp. strain ADP1 through pathways encoded by genes in the dca-pca-qui-pob chromosomal cluster. In an appropriate genetic background, it was possible to select for an Acinetobacter strain that had lost the ability to grow with caffeate, a commonly occurring hydroxycinnamate. The newly identified mutation was shown to be a deletion in a gene designated hcaC and encoding a ligase required for conversion of commonly occurring hydroxycinnamates (caffeate, ferulate, coumarate, and 3,4-dihydroxyphenylpropionate) to thioesters. Linkage analysis showed that hcaC is linked to pobA. Downstream from hcaC and transcribed in the direction opposite the direction of pobA transcription are open reading frames designated hcaDEFG. Functions of these genes were inferred from sequence comparisons and from the properties of knockout mutants. HcaD corresponded to an acyl coenzyme A (acyl-CoA) dehydrogenase required for conversion of 3,4-dihydroxyphenylpropionyl-CoA to caffeoyl-CoA. HcaE appears to encode a member of a family of outer membrane proteins known as porins. Knockout mutations in hcaF confer no discernible phenotype. Knockout mutations in hcaG indicate that this gene encodes a membrane-associated esterase that hydrolyzes chlorogenate to quinate, which is metabolized in the periplasm, and caffeate, which is metabolized by intracellular enzymes. The chromosomal location of hcaG, between hcaC (required for growth with caffeate) and quiA (required for growth with quinate), provided the essential clue that led to the genetic test of HcaG as the esterase that produces caffeate and quinate from chlorogenate. Thus, in this study, organization within what is now established as the dca-pca-qui-pob-hca chromosomal cluster provided essential information about the function of genes in the environment.