Cloning and expression of a Clostridium thermocellum xylanase gene in Escherichia coli

A Clostridium thermocellum xylanase gene, designated xynX, was cloned in Escherichia coli and was categorized a novel gene as a result of the comparison of restriction patterns of the C. thermocellum xylanase genes so far reported. The xynX gene encodes a xylanase having the molecular weight of 105 kilodaltons. A number of smaller truncated proteins with activities towards 4-methylumbelliferyl-beta-D-cellobioside and xylan were also produced. The enzyme hydrolyzed xylan to xylo-oligosaccharide, indicating typical activity of endo-beta-1,4-xylanase. This endoxylanase hydrolyzed carboxymethylcellulose without notable reduction of the viscosity as an exo-beta-1,4-glucanase, even though the enzyme exhibited very low levels of activity against other soluble and insoluble cellulosic substrates.