Mine Shouhei, Watanabe Masahiro, Kamachi Saori, Abe Yoshito, Ueda Tadashi
From the Biomedical Research Institute (BMD), National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577,
the Research Institute for Sustainable Chemistry (ISC), AIST, 3-11-32 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, and
J Biol Chem. 2017 Mar 24;292(12):4996-5006. doi: 10.1074/jbc.M116.766535. Epub 2017 Jan 27.
The archaeal exo-β-d-glucosaminidase (GlmA) is a dimeric enzyme that hydrolyzes chitosan oligosaccharides into monomer glucosamines. GlmA is a member of the glycosidase hydrolase (GH)-A superfamily-subfamily 35 and is a novel enzyme in terms of its primary structure. Here, we present the crystal structure of GlmA in complex with glucosamine at 1.27 Å resolution. The structure reveals that a monomeric form of GlmA shares structural homology with GH42 β-galactosidases, whereas most of the spatial positions of the active site residues are identical to those of GH35 β-galactosidases. We found that upon dimerization, the active site of GlmA changes shape, enhancing its ability to hydrolyze the smaller substrate in a manner similar to that of homotrimeric GH42 β-galactosidase. However, GlmA can differentiate glucosamine from galactose based on one charged residue while using the "evolutionary heritage residue" it shares with GH35 β-galactosidase. Our study suggests that GH35 and GH42 β-galactosidases evolved by exploiting the structural features of GlmA.
古菌外切-β-D-氨基葡萄糖苷酶（GlmA）是一种二聚体酶，可将壳寡糖水解为单体氨基葡萄糖。GlmA是糖苷水解酶（GH）-A超家族35亚家族的成员，就其一级结构而言是一种新型酶。在此，我们展示了GlmA与氨基葡萄糖复合物的晶体结构，分辨率为1.27 Å。该结构表明，GlmA的单体形式与GH42β-半乳糖苷酶具有结构同源性，而活性位点残基的大多数空间位置与GH35β-半乳糖苷酶相同。我们发现，二聚化后，GlmA的活性位点会改变形状，以类似于同三聚体GH42β-半乳糖苷酶的方式增强其水解较小底物的能力。然而，GlmA可以基于一个带电荷的残基区分氨基葡萄糖和半乳糖，同时利用其与GH35β-半乳糖苷酶共有的“进化遗传残基”。我们的研究表明，GH35和GH42β-半乳糖苷酶是通过利用GlmA的结构特征进化而来的。
