Department of Bioscience and Biotechnology, Fukui Prefectural University, 4-1-1 Matsuokakenjyoujima, Eiheiji-cho, Yoshida-gun, Fukui, 910-1195, Japan.
Department of Biotechnology, College of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan.
Biochem Biophys Res Commun. 2020 Dec 17;533(4):1170-1176. doi: 10.1016/j.bbrc.2020.09.133. Epub 2020 Oct 9.
α-1,3-Glucan is a homopolymer composed of D-glucose (Glc) and it is an extracellular polysaccharide found in dental plaque due to Streptococcus species. α-1,3-Glucanase from Streptomyces thermodiastaticus strain HF3-3 (Agl-ST) has been identified as a thermostable α-1,3-glucanase, which is classified into glycoside hydrolase family 87 (GH87) and specifically hydrolyzes α-1,3-glucan with an endo-action. The enzyme has a potential to inhibit the production of dental plaque and to be used for biotechnological applications. Here we show the structure of the catalytic unit of Agl-ST determined at 1.16 Å resolution using X-ray crystallography. The catalytic unit is composed of two modules, a β-sandwich fold module, and a right-handed β-helix fold module, which resembles other structural characterized GH87 enzymes from Bacillus circulans str. KA-304 and Paenibacillus glycanilyticus str. FH11, with moderate sequence identities between each other (approximately 27% between the catalytic units). However, Agl-ST is smaller in size and more thermally stable than the others. A disulfide bond that anchors the C-terminal coil of the β-helix fold, which is expected to contribute to thermal stability only exists in the catalytic unit of Agl-ST.
α-1,3-葡聚糖是一种由 D-葡萄糖（Glc）组成的均聚物，它是一种存在于牙菌斑中的胞外多糖，由链球菌属产生。来自嗜热链霉菌 HF3-3 的α-1,3-葡聚糖酶（Agl-ST）已被鉴定为一种耐热的α-1,3-葡聚糖酶，属于糖苷水解酶家族 87（GH87），特异性地以内切方式水解α-1,3-葡聚糖。该酶具有抑制牙菌斑生成和用于生物技术应用的潜力。在这里，我们使用 X 射线晶体学确定了 Agl-ST 的催化单元在 1.16 Å分辨率下的结构。催化单元由两个模块组成，一个β-三明治折叠模块和一个右手β-螺旋折叠模块，与来自环状芽孢杆菌 str. KA-304 和粘质沙雷氏菌 str. FH11 的其他结构特征的 GH87 酶相似，彼此之间具有中等序列同一性（催化单元之间约为 27%）。然而，Agl-ST 的尺寸较小，且比其他酶更耐热。只有 Agl-ST 的催化单元中存在一个二硫键，该键锚定β-螺旋折叠的 C 端卷曲，预计仅对热稳定性有贡献。
