open access

https://hdl.handle.net/2115/22096

Structural insights into unique substrate selectivity of Thermoplasma acidophilum D-aldohexose dehydrogenase

英語

Thermoplasma acidophilum

2007-04-06

Elsevier

Journal of Molecular Biology

367(4)

1034-1046

The 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.

学術雑誌論文

Accepted Manuscript

0022-2836

1089-8638