Abstract
BackgroundXylanase-containing enzyme cocktails are used on an industrial scale to convert xylan into value-added products, as they hydrolyse the β-1,4-glycosidic linkages between xylopyranosyl residues. In the present study, we focused on xynS1, the glycoside hydrolase (GH) 11 xylanase gene derived from the Streptomyces sp. strain J103, which can mediate XynS1 protein synthesis and lignocellulosic material hydrolysis.ResultsxynS1 has an open reading frame with 693 base pairs that encodes a protein with 230 amino acids. The predicted molecular weight and isoelectric point of the protein were 24.47 kDa and 7.92, respectively. The gene was cloned into the pET-11a expression vector and expressed in Escherichia coli BL21(DE3). Recombinant XynS1 (rXynS1) was purified via His-tag affinity column chromatography. rXynS1 exhibited optimal activity at a pH of 5.0 and temperature of 55 °C. Thermal stability was in the temperature range of 50–55 °C. The estimated Km and Vmax values were 51.4 mg/mL and 898.2 U/mg, respectively. One millimolar of Mn2+ and Na+ ions stimulated the activity of rXynS1 by up to 209% and 122.4%, respectively, and 1 mM Co2+ and Ni2+ acted as inhibitors of the enzyme. The mixture of rXynS1, originates from Streptomyces sp. strain J103 and acetyl xylan esterase (AXE), originating from the marine bacterium Ochrovirga pacifica, enhanced the xylan degradation by 2.27-fold, compared to the activity of rXynS1 alone when Mn2+ was used in the reaction mixture; this reflected the ability of both enzymes to hydrolyse the xylan structure. The use of an enzyme cocktail of rXynS1, AXE, and commercial cellulase (Celluclast® 1.5 L) for the hydrolysis of lignocellulosic biomass was more effective than that of commercial cellulase alone, thereby increasing the relative activity 2.3 fold.ConclusionThe supplementation of rXynS1 with AXE enhanced the xylan degradation process via the de-esterification of acetyl groups in the xylan structure. Synergetic action of rXynS1 with commercial cellulase improved the hydrolysis of pre-treated lignocellulosic biomass; thus, rXynS1 could potentially be used in several industrial applications.
Highlights
Xylanase-containing enzyme cocktails are used on an industrial scale to convert xylan into valueadded products, as they hydrolyse the β-1,4-glycosidic linkages between xylopyranosyl residues
Results of similarity and identity analysis of the Xylanase protein (XynS1) amino acid sequence obtained from Streptomyces sp. strain J103 revealed that XynS1 exhibited 73.2% identity and 85.7% similarity with the characterised endo-1,4-beta-xylanase precursor of Streptomyces sp
XynS1 shared 70.7% and 68.2% amino acid sequence identities with characterised xylanases from Streptomyces rameus and Streptomyces sp
Summary
Xylanase-containing enzyme cocktails are used on an industrial scale to convert xylan into valueadded products, as they hydrolyse the β-1,4-glycosidic linkages between xylopyranosyl residues. Hemicellulose, which acts as a physical shield covering cellulose fibres, is one of the major factors responsible for this recalcitrant nature [3, 4] It is composed of a heterogeneous mixture of xylan, xyloglucan, mannans, and glucomannans [5]; xylan was identified to be the most abundant hemicellulose in lignocellulosic biomass [6]. The complex and heterogenic structure of xylan is targeted by several xylolytic enzymes that exhibit synergetic activity; these enzymes include endo-1,4-β-xylanase (EC 3.2.1.8) and 1,4-β-xylosidase (EC 3.2.1.37) They act as the key enzymes that cleave the β-1,4-glycosidic linkages between xylopyranosyl residues and α-D glucuronidases (EC 3.2.1.139), α-Larabinofuranosidase (EC 3.2.1.55), acetylxylan esterase (EC 3.1.1.72), and ferulic acid esterase (EC 3.1.1.73), for the hydrolysis of side chains (http://www.cazy.org), [12, 13]. Based on the results of amino acid sequence analysis [14] xylanases are categorised into the following glycosyl hydrolase (GH) families: 5, 7, 8, 10, 11, 43, and 52; the majority of studied xylanases belong to the GH 10 and GH 11 families (http://www.cazy.org) [12, 15]
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