Okazaki Nobuo, Blaber Michael, Kuroki Ryota, Tamada Taro
Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society, 162-1 Shirakata, Tokai, Ibaraki 319-1106, Japan.
College of Medicine, Florida State University, 1115 West Call Street, Tallahassee, FL 32306-4300, USA.
Acta Crystallogr F Struct Biol Commun. 2018 Nov 1;74(Pt 11):741-746. doi: 10.1107/S2053230X1801453X. Epub 2018 Oct 31.
Glycosyltrehalose synthase (GTSase) converts the glucosidic bond between the last two glucose residues of amylose from an α-1,4 bond to an α-1,1 bond, generating a nonreducing glycosyl trehaloside, in the first step of the biosynthesis of trehalose. To better understand the structural basis of the catalytic mechanism, the crystal structure of GTSase from the hyperthermophilic archaeon Sulfolobus shibatae DSM5389 (5389-GTSase) has been determined to 2.4 Å resolution by X-ray crystallography. The structure of 5389-GTSase can be divided into five domains. The central domain contains the (β/α)-barrel fold that is conserved as the catalytic domain in the α-amylase family. Three invariant catalytic carboxylic amino acids in the α-amylase family are also found in GTSase at positions Asp241, Glu269 and Asp460 in the catalytic domain. The shape of the catalytic cavity and the pocket size at the bottom of the cavity correspond to the intramolecular transglycosylation mechanism proposed from previous enzymatic studies.
糖基海藻糖合酶（GTSase）在海藻糖生物合成的第一步中，将直链淀粉最后两个葡萄糖残基之间的糖苷键从α-1,4键转化为α-1,1键，生成一种非还原性糖基海藻糖。为了更好地理解催化机制的结构基础，通过X射线晶体学已确定嗜热古菌柴田硫化叶菌DSM5389（5389-GTSase）的GTSase晶体结构，分辨率为2.4 Å。5389-GTSase的结构可分为五个结构域。中央结构域包含（β/α）-桶状折叠，在α-淀粉酶家族中作为催化结构域保守存在。在GTSase的催化结构域中，还在第241位天冬氨酸、第269位谷氨酸和第460位天冬氨酸位置发现了α-淀粉酶家族中三个不变的催化性羧基氨基酸。催化腔的形状以及腔底部的口袋大小与先前酶学研究提出的分子内转糖基化机制相对应。
