Gene Expression and Molecular Characterization of a Xylanase from Chicken Cecum Metagenome

A xylanase gene xynA(MG1) with a 1,116-bp open reading frame, encoding an endo-beta-1,4-xylanase, was cloned from a chicken cecum metagenome. The translated XynA(MG1) protein consisted of 372 amino acids including a putative signal peptide of 23 amino acids. The calculated molecular mass of the mature XynA(MG1) was 40,013Da, with a theoretical pI value of 5.76. The amino acid sequence of XynA(MG1) showed 59% identity to endo-beta-1,4-xylanase from Prevotella bryantii and Prevotella ruminicola and 58% identity to that from Prevotella copri. XynA(MG1) has two conserved motifs, DVVNE and TEXD, containing two active site glutamates and an invariant asparagine, characteristic of GH10 family xylanase. The xynA(MG1) gene without signal peptide sequence was cloned and fused with thioredoxin protein (Trx.Tag) in pET-32a plasmid and overexpressed in Escherichia coli Tuner (TM)(DE3) pLysS. The purified mature XynA(MG1) was highly salt-tolerant and stable and displayed higher than 96% of its catalytic activity in the reaction containing 1 to 4M NaCl. It was only slightly affected by common organic solvents added in aqueous solution to up to 5M. This chicken cecum metagenome-derived xylanase has potential applications in animal feed additives and industrial enzymatic processes requiring exposure to high concentrations of salt and organic solvents.