Characterization of glycoside hydrolases involved in xyloglucan degradation in the thermophilic bacterium Thermotoga maritima

Xyloglucan, a plant hemicellulosic polysaccharide, has a β-glucan main chain and complex side chains composed of sugars such as xylose, galactose and fucose. In this study, we identified xyloglucan degradation-related enzymes in the thermophilic bacterium Thermotoga maritima. TmCel74, belonging to glycoside hydrolase (GH) family 74, was found to be an endo-processive-type xyloglucanase that degraded xyloglucan into xyloglucan oligosaccharides and was able to cleave the β-glucan main chain at both unbranched and xylosylated glucosyl residues. The gene locus of TmCel74 was located near the loci encoding α-L-fucosidase (GH29), α-xylosidase TmAxy31 (GH31), and β-galactosidase TmBgalB (GH42). TmAxy31 and TmBgalB released xylosyl and galactosyl residues, respectively, from xyloglucan oligosaccharides, but not from xyloglucan polysaccharides, indicating that these exo-type glycoside hydrolases cooperatively degrade the side chains of xyloglucan oligosaccharides produced from xyloglucan by TmCel74. Our findings shed light on the complex genetic locus required for xyloglucan degradation in T. maritima.