Kawai Yuzuki, Kameyama Akihiko, Sakuraba Haruhiko, Matsuzawa Tomohiko
Faculty of Agriculture, Department of Applied Biological Science , Kagawa University, 2393 Ikenobe, Miki, 761-0795, Kagawa, Japan.
Cellular and Molecular Biotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, 305-8565, Ibaraki, Japan.
Sci Rep. 2025 Jun 6;15(1):19922. doi: 10.1038/s41598-025-05366-6.
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.
木葡聚糖是一种植物半纤维素多糖，具有β-葡聚糖主链和由木糖、半乳糖和岩藻糖等糖类组成的复杂侧链。在本研究中，我们在嗜热细菌海栖热袍菌中鉴定出了与木葡聚糖降解相关的酶。属于糖苷水解酶（GH）家族74的TmCel74被发现是一种内切渐进型木葡聚糖酶，它能将木葡聚糖降解为木葡聚糖寡糖，并能够在无分支和木糖基化的葡萄糖残基处切割β-葡聚糖主链。TmCel74的基因座位于编码α-L-岩藻糖苷酶（GH29）、α-木糖苷酶TmAxy31（GH31）和β-半乳糖苷酶TmBgalB（GH42）的基因座附近。TmAxy31和TmBgalB分别从木葡聚糖寡糖中释放木糖基和半乳糖基残基，但不从木葡聚糖多糖中释放，这表明这些外切型糖苷水解酶协同降解由TmCel74从木葡聚糖产生的木葡聚糖寡糖的侧链。我们的研究结果揭示了海栖热袍菌中木葡聚糖降解所需的复杂基因座。
