2024-03-29T10:55:32Zhttps://eprints.lib.hokudai.ac.jp/dspace-oai/requestoai:eprints.lib.hokudai.ac.jp:2115/220962022-11-17T02:08:08Zhdl_2115_20046hdl_2115_138Structural insights into unique substrate selectivity of Thermoplasma acidophilum D-aldohexose dehydrogenaseYasutake, YoshiakiNishiya, YoshiakiTamura, NorikoTamura, TomohiroD-aldohexose dehydrogenaseD-glucose dehydrogenaseD-mannoseshort-chain dehydrogenase/reductase (SDR)Thermoplasma acidophilum464The D-aldohexose dehydrogenase from the thermoacidophilic archaea Thermoplasma acidophilum (AldT) belongs to the short-chain dehydrogenase/reductase (SDR) superfamily and catalyzes the oxidation of several monosaccharides with a preference for NAD+ rather than NADP+ as a cofactor. It has been found that AldT is a unique enzyme that exhibits the highest dehydrogenase activity against D-mannose. Here, we describe the crystal structures of AldT in ligand-free form, in complex with NADH, and in complex with the substrate D-mannose, at 2.1 Å, 1.65 Å, and 1.6 Å resolution, respectively. The AldT subunit forms a typical SDR fold with an unexpectedly long C-terminal tail and assembles into an intertwined tetramer. The D-mannose complex structure reveals that Glu84 interacts with the axial C2 hydroxyl group of the bound D-mannose. Structural comparison with Bacillus megaterium glucose dehydrogenase (BmGlcDH) suggests that the conformation of the glutamate side-chain is crucial for discrimination between D-mannose and its C2 epimer D-glucose, and the conformation of the glutamate side-chain depends on the spatial arrangement of nearby hydrophobic residues that do not directly interact with the substrate. Elucidation of the D-mannose recognition mechanism of AldT further provides structural insights into the unique substrate selectivity of AldT. Finally, we show that the extended C-terminal tail completely shuts the substrate-binding pocket of the neighboring subunit both in the presence and absence of substrate. The elaborate inter-subunit interactions between the C-terminal tail and the entrance of the substrate-binding pocket imply that the tail may play a pivotal role in the enzyme activity.ElsevierJournal Articleapplication/pdfhttp://hdl.handle.net/2115/22096https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/22096/1/JMB367-4.pdf0022-28361089-8638Journal of Molecular Biology3674103410462007-04-06enginfo:pmid/17300803info:doi/10.1016/j.jmb.2007.01.029author