Yaoi Katsuro, Kondo Hidemasa, Noro Natsuko, Suzuki Mamoru, Tsuda Sakae, Mitsuishi Yasushi
Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan.
Structure. 2004 Jul;12(7):1209-17. doi: 10.1016/j.str.2004.04.020.
Oligoxyloglucan reducing-end-specific cellobiohydrolase (OXG-RCBH; EC 3.2.1.150) is an exoglucanase that recognizes the reducing end of oligoxyloglucan and releases two glucosyl residue segments from the main chain. The X-ray crystal structure of OXG-RCBH determined at 2.2 A resolution reveals a unique feature of this enzyme; OXG-RCBH consists of a tandem repeat of two similar domains, which are both folded into seven-bladed beta-propeller structures. The sequence alignment of the propeller blades, based on the structure, indicates that a weak repeat of the amino acid sequence occurred seven times to construct each domain. There is a cleft that can accommodate the substrate oligosaccharide between the two domains, which is a putative substrate binding subsite. Mutation of either Asp35 or Asp465, located in the putative catalytic center, to Asn resulted in a protein with no detectable catalytic activity, indicating the critical role of these amino acids in catalysis.
低聚木葡聚糖还原端特异性纤维二糖水解酶（OXG-RCBH；EC 3.2.1.150）是一种外切葡聚糖酶，它识别低聚木葡聚糖的还原端，并从主链上释放出两个葡萄糖基残基片段。以2.2 Å分辨率测定的OXG-RCBH的X射线晶体结构揭示了这种酶的一个独特特征；OXG-RCBH由两个相似结构域的串联重复组成，这两个结构域都折叠成七叶β-螺旋桨结构。基于该结构的螺旋桨叶片序列比对表明，氨基酸序列的弱重复出现了七次以构建每个结构域。在两个结构域之间有一个可容纳底物寡糖的裂隙，这是一个假定的底物结合亚位点。位于假定催化中心的Asp35或Asp465突变为Asn会导致蛋白质没有可检测到的催化活性，表明这些氨基酸在催化中起关键作用。
