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Xylanases with enhanced thermophilicity and alkalophilicity

Inactive Publication Date: 2009-03-19
NAT RES COUNCIL OF CANADA
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0012]The present invention relates to xylanases. More specifically, the invention relates to xylanases, and modified xylanases with improved performance at conditions of high temperature and pH.
[0013]This invention relates to a xylanase comprising at least one substituted amino acid residue at a position selected from the group consisting of amino acid 11, 116, 118, 144, and 161, with the position determined from sequence alignment of the modified xylanase with Trichoderma reesei xylanase II amino acid sequence defined in SEQ ID NO:16. Preferably, the xylanase exhibits improved thermophilicity, alkalophilicity, broader effective pH range, expression efficiency or a combination thereof, in comparison to a corresponding native TrX xylanase.
[0044]The present invention is directed to the use of the modified xylanase as defined above in an industrial process. Also included is an industrial process, wherein the industrial process comprises bleaching of pulp, processing of precision devices. or improving digestibility of poultry and swine feed.

Problems solved by technology

In the manufacturing of pulp for the production of paper, fibrous material is subjected to high temperatures and pressures in the presence of chemicals.
This in turn decreases the chlorinated effluent produced by such processes.
A drawback of many commercially available wild-type xylanases, is that these enzymes exhibit an acidic pH optimum and a temperature optimum of about 55° C. Therefore, in order to effectively utilize xylanases for bleaching applications, the pulp must be acidified to a pH approximating the optimal pH for the specific xylanase used.
Decreasing pulp temperatures for xylanase treatment decreases the efficiency of the subsequent chemical bleaching.
Further, the addition of acids leads to corrosion, which lessens the lifetime of process equipment.
However, these thermostable xylanase enzymes are large, with molecular masses ranging from 35-120 kDa (320-1100 residues), and exhibit a reduced ability to penetrate the pulp mass compared with other smaller xylanases which exhibit better accessibility to pulp fibers.
This additional cellulolytic activity is undesirable for pulp bleaching, due to its detrimental effect on cellulose, the bulk material in paper.
Furthermore, hyper-thermostable xylanase enzymes which function normally at extremely high temperatures have low specific activities at temperatures in the range for optimal pulp bleaching (Simpson et al.
However, the use of these enzymes within industrial applications still requires cooling and acidification of pulp following pretreatment, prior to enzyme addition.
However, these mutations including N11D also have an adverse effect on both the thermophilicity and the alkalophilicity of the xylanase, resulting in a decrease of enzymatic activity at higher temperatures and the neutral-alkaline pH, as compared to native TrX II.

Method used

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  • Xylanases with enhanced thermophilicity and alkalophilicity
  • Xylanases with enhanced thermophilicity and alkalophilicity
  • Xylanases with enhanced thermophilicity and alkalophilicity

Examples

Experimental program
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Effect test

example 1

Construction of Trichoderma reesei Mutant Xylanases

[0129]Basic recombinant DNA methods like plasmid preparation, restriction enzyme digestion, polymerase chain reaction, oligonucleotide phosphorylation, ligation, transformation and DNA hybridization were performed according to well-established protocols familiar to those skilled in the art (e.g. Sung et al., 1986) or as recommended by the manufacturer of the enzymes or kit. The buffers for many enzymes have been supplied as part of a kit or made according to the manufacturer's instructions. Restriction enzymes, T4 polynucleotide kinase and T4 DNA ligase were purchased from New England Biolabs Lid, Mississauga, Ont. GeneAmp PCR reagent kit was purchased from Perkin-Elmer. A precursor plasmid pXYbc, which is a pUC type plasmid with a Bacillus circulans xylanase gene inserted, has previously been prepared and published (Sung et al, 1993; Campbell et al., U.S. Pat. No. 5,405,769). A commonly used E. coli strain, HB101 (Clonetech Lab, Pa...

example 2

Characterization of Mutant Xylanases

2-1: Production of Xylanases

[0196]The culture conditions comprised a 5 ml culture of overnight innoculant in 2YT medium (16 g bacto-tryptone, 10 g yeast extract, 5 g NaCl, 1 L of water) containing ampicillin (100 mg / L) was added to 2YT medium (1 L) with ampicillin. The cultures were grown with shaking (200 rpm) at 37° C. After 16 hr, cells were harvested.

2-2: Purification of Mutant Xylanases

[0197]Protein samples were prepared from cells by first making an extract of the cells by grinding 10 g of the cell paste with 25 g of alumina powder. After grinding to smooth mixture, small amounts (5 mL) of ice cold buffer A (10 mM sodium acetate, pH 5.5 for BcX mutants) or buffer B (10 mM sodium acetate, pH 4.6 for TX mutants) were added and the mixture ground vigorously between additions. The alumina and cell debris were removed by centrifugation of the mixture at 8000×g for 30 min.

[0198]Prior to column chromatography, the supernatant was adjusted to pH 4.6...

example 3

Thermophilicity of Mutant Xylanases

[0206]Thermophilicity was examined to test the effect of different temperatures on the enzymatic hydrolysis of soluble xylan by different mutant xylanases.

[0207]The assay procedure was similar to the standard assay with changes in the incubation temperature and time. The xylanases (15 μg / mL) and soluble birchwood xylan substrate, in 50 mM sodium citrate buffer of pH 5.5, were mixed and incubated in a circulating water bath at different temperatures. After a 30-min incubation, the amount of reducing sugars released from xylan was determined by HBAH analysis and was calculated as a relative activity, with the value at 40° C. representing 100%.

[0208]The effect of temperature on the hydrolysis of xylan by TrX-HML-75A105H-125A129E-144R (TrX-HML-AHAE-R) is shown in FIG. 3. Compared to the precursor without the H144R mutation (TrX-HML-AHAE), this mutant xylanase showed a moderately improved enzymatic activity at higher temperature. These results suggest t...

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Abstract

The present invention provides a xylanase, or a modified xylanase enzyme comprising at least one substituted amino acid residue at a position selected from the group consisting of amino acid 11, 116, 118, 144 and 161, the position determined from sequence alignment of the modified xylanase with Trichoderma reesei xylanase II amino acid sequence. The xylanases described herein exhibit improved thermophilicity, alkalophilicity, expression efficiency, or a combination thereof, in comparison to a corresponding native xylanase.

Description

[0001]The present invention relates to xylanases. More specifically, the invention relates to xylanases, and modified xylanases with improved performance at conditions of high temperature and pH.BACKGROUND OF THE INVENTION[0002]Xylanases are a group of enzymes with wide commercial utility. A major application of xylanases is for pulp biobleaching in the production of paper. In addition, xylanases have been used as clarifying agents in juices and wines, as enzymatic agents in the washing of precision devices an 4 semiconductors (e.g. U.S. Pat. No. 5,078,802), and they are also used for improving digestibility of poultry and swine feed.[0003]In the manufacturing of pulp for the production of paper, fibrous material is subjected to high temperatures and pressures in the presence of chemicals. This treatment converts the fibers to pulp and is known as pulping. Following pulping, the pulp is bleached. Xylanase enzymes are used to enhance the bleaching of the pulp. The xylanase treatment ...

Claims

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Application Information

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IPC IPC(8): C12N9/24C12P21/06C07H21/04C12N1/18D21C5/00D21C9/10
CPCC12Y302/01008C12N9/2482D21C9/1036D21C5/005C12N9/248
Inventor SUNG, WING L.
Owner NAT RES COUNCIL OF CANADA
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