Gene_locus Report for: aspng-faeb

The faeB gene encoding a second feruloyl esterase from Aspergillus niger has been cloned and characterized. It consists of an open reading frame of 1644 bp containing one intron. The gene encodes a protein of 521 amino acids that has sequence similarity to that of an Aspergillus oryzae tannase. However, the encoded enzyme, feruloyl esterase B (FAEB), does not have tannase activity. Comparison of the physical characteristics and substrate specificity of FAEB with those of a cinnamoyl esterase from A. niger [Kroon, Faulds and Williamson (1996) Biotechnol. Appl. Biochem. 23, 255-262] suggests that they are in fact the same enzyme. The expression of faeB is specifically induced in the presence of certain aromatic compounds, but not in the presence of other constituents present in plant-cell-wall polysaccharides such as arabinoxylan or pectin. The expression profile of faeB in the presence of aromatic compounds was compared with the expression of A. niger faeA, encoding feruloyl esterase A (FAEA), and A. niger bphA, the gene encoding a benzoate-p-hydroxylase. All three genes have different subsets of aromatic compounds that induce their expression, indicating the presence of different transcription activating systems in A. niger that respond to aromatic compounds. Comparison of the activity of FAEA and FAEB on sugar-beet pectin and wheat arabinoxylan demonstrated that they are both involved in the degradation of both polysaccharides, but have opposite preferences for these substrates. FAEA is more active than FAEB towards wheat arabinoxylan, whereas FAEB is more active than FAEA towards sugar-beet pectin.

An inducible esterase has been isolated from a liquid culture of Aspergillus niger grown on sugar-beet pulp. The enzyme was active on methyl esters of cinnamic acids, caffeic > p-coumaric > ferulic, and is therefore termed a cinnamoyl esterase. The enzyme was not active on methyl sinapinate, a good substrate for ferulic acid esterase III, which was purified previously from A. niger [Faulds and Williamson (1994) Microbiology 140, 779-787]. With methyl caffeate as substrate the enzyme had temperature and pH optima of 50 degrees C and 6.0 respectively, and a specific activity of 96.9 units per mg of protein. The purified protein (native molecular mass 145 000 Da) gave a single heavily stained band on SDS/PAGE, suggesting the protein was a dimer, and seemed to be heavily glycosylated. Isoelectric focusing gave a single band corresponding to a pl of 4.80. The pure enzyme was free of other carbohydrase activities. The activity of the pure enzyme was inhibited by more than 99% after treatment with the serine-specific protease inhibitor aminoethylbenzenesulphonylfluoride (1 mM) for 12 h. The enzyme was capable of releasing ferulic acid from sugar beet pulp.

The activity of two forms of ferulic acid esterase (FAE) from Aspergillus niger on a synthetic feruloylated substrate (methyl ferulate) and on 11 different feruloylated oligosaccharides from sugar-beet pulp and wheat bran was determined. The enzymes exhibited different specificities for the various feruloylated substrates and were more active on certain substrates of cell-wall origin than on methyl ferulate. Both enzymes preferred the arabinose residue to which ferulic acid is attached in the furanose form. FAE-I had no clear preference for the type of linkage involved between the ferulic acid units and the oligosaccharide chain. In contrast, FAE-III had a clear requirement for ferulic acid to be attached to O-5 of the Ara f ring while no catalysis was observed when ferulic acid was attached to O-2. Both enzymes showed maximum activity on feruloylated trisaccharides. An increase in the length of the oligosaccharide chain did not preclude catalysis, but feruloylated oligosaccharides of a dp > 3 were hydrolysed at a reduced rate. Our results support the hypothesis that different kinds of ferulic acid esterases exist with different specificities for the oligosaccharide chain of the feruloylated substrates.

The filamentous fungus Aspergillus niger is widely exploited by the fermentation industry for the production of enzymes and organic acids, particularly citric acid. We sequenced the 33.9-megabase genome of A. niger CBS 513.88, the ancestor of currently used enzyme production strains. A high level of synteny was observed with other aspergilli sequenced. Strong function predictions were made for 6,506 of the 14,165 open reading frames identified. A detailed description of the components of the protein secretion pathway was made and striking differences in the hydrolytic enzyme spectra of aspergilli were observed. A reconstructed metabolic network comprising 1,069 unique reactions illustrates the versatile metabolism of A. niger. Noteworthy is the large number of major facilitator superfamily transporters and fungal zinc binuclear cluster transcription factors, and the presence of putative gene clusters for fumonisin and ochratoxin A synthesis.

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.

The faeB gene encoding a second feruloyl esterase from Aspergillus niger has been cloned and characterized. It consists of an open reading frame of 1644 bp containing one intron. The gene encodes a protein of 521 amino acids that has sequence similarity to that of an Aspergillus oryzae tannase. However, the encoded enzyme, feruloyl esterase B (FAEB), does not have tannase activity. Comparison of the physical characteristics and substrate specificity of FAEB with those of a cinnamoyl esterase from A. niger [Kroon, Faulds and Williamson (1996) Biotechnol. Appl. Biochem. 23, 255-262] suggests that they are in fact the same enzyme. The expression of faeB is specifically induced in the presence of certain aromatic compounds, but not in the presence of other constituents present in plant-cell-wall polysaccharides such as arabinoxylan or pectin. The expression profile of faeB in the presence of aromatic compounds was compared with the expression of A. niger faeA, encoding feruloyl esterase A (FAEA), and A. niger bphA, the gene encoding a benzoate-p-hydroxylase. All three genes have different subsets of aromatic compounds that induce their expression, indicating the presence of different transcription activating systems in A. niger that respond to aromatic compounds. Comparison of the activity of FAEA and FAEB on sugar-beet pectin and wheat arabinoxylan demonstrated that they are both involved in the degradation of both polysaccharides, but have opposite preferences for these substrates. FAEA is more active than FAEB towards wheat arabinoxylan, whereas FAEB is more active than FAEA towards sugar-beet pectin.

An inducible esterase has been isolated from a liquid culture of Aspergillus niger grown on sugar-beet pulp. The enzyme was active on methyl esters of cinnamic acids, caffeic > p-coumaric > ferulic, and is therefore termed a cinnamoyl esterase. The enzyme was not active on methyl sinapinate, a good substrate for ferulic acid esterase III, which was purified previously from A. niger [Faulds and Williamson (1994) Microbiology 140, 779-787]. With methyl caffeate as substrate the enzyme had temperature and pH optima of 50 degrees C and 6.0 respectively, and a specific activity of 96.9 units per mg of protein. The purified protein (native molecular mass 145 000 Da) gave a single heavily stained band on SDS/PAGE, suggesting the protein was a dimer, and seemed to be heavily glycosylated. Isoelectric focusing gave a single band corresponding to a pl of 4.80. The pure enzyme was free of other carbohydrase activities. The activity of the pure enzyme was inhibited by more than 99% after treatment with the serine-specific protease inhibitor aminoethylbenzenesulphonylfluoride (1 mM) for 12 h. The enzyme was capable of releasing ferulic acid from sugar beet pulp.

The activity of two forms of ferulic acid esterase (FAE) from Aspergillus niger on a synthetic feruloylated substrate (methyl ferulate) and on 11 different feruloylated oligosaccharides from sugar-beet pulp and wheat bran was determined. The enzymes exhibited different specificities for the various feruloylated substrates and were more active on certain substrates of cell-wall origin than on methyl ferulate. Both enzymes preferred the arabinose residue to which ferulic acid is attached in the furanose form. FAE-I had no clear preference for the type of linkage involved between the ferulic acid units and the oligosaccharide chain. In contrast, FAE-III had a clear requirement for ferulic acid to be attached to O-5 of the Ara f ring while no catalysis was observed when ferulic acid was attached to O-2. Both enzymes showed maximum activity on feruloylated trisaccharides. An increase in the length of the oligosaccharide chain did not preclude catalysis, but feruloylated oligosaccharides of a dp > 3 were hydrolysed at a reduced rate. Our results support the hypothesis that different kinds of ferulic acid esterases exist with different specificities for the oligosaccharide chain of the feruloylated substrates.