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Biochemical and structural characterization of quinoprotein aldose sugar dehydrogenase from Thermus thermophilus HJ6: Mutational analysis of Tyr156 in the substrate-binding site

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Title
Biochemical and structural characterization of quinoprotein aldose sugar dehydrogenase from Thermus thermophilus HJ6: Mutational analysis of Tyr156 in the substrate-binding site
Authors
Kim, Han-Woo
Wang, Ji-Yeon
Lee, Ji-Yeon
Park, Ae Kyung
Park, Hyun
Jeon, Sung-Jong
Subject
Biochemistry & Molecular Biology; Biophysics
Keywords
Thermus thermophilus; Aldose sugar dehydrogenase; Soluble quinoprotein glucose; Dehydrogenase; Alcohol oxidation
Issue Date
2016
Citation
Kim, Han-Woo, et al. 2016. "Biochemical and structural characterization of quinoprotein aldose sugar dehydrogenase from Thermus thermophilus HJ6: Mutational analysis of Tyr156 in the substrate-binding site". Archives of Biochemistry and Biophysics, 608: 20-26.
Abstract
The gene encoding a quinoprotein aldose sugar dehydrogenase (ASD) from Thermus thermophilus HJ6 (Tt_ASD) was cloned and sequenced; it comprised 1059 nucleotides encoding a protein containing 352 amino acids that had a predicted molecular mass of 38.9 kDa. The deduced amino acid sequence showed 42.9% and 33.9% identities to the ASD proteins from Pyrobaculum aerophilum and Escherichia coli, respectively. The biochemical properties of Tt_ASD were characterized. The optimum pH for the oxidation of glucose was 7.0-7.5 and the optimum temperature was 70℃. The half-life of heat inactivation for the apoenzyme was about 25 min at 85 ℃. The enzyme was highly thermostable, and the activity of the pyrroloquinoline quinone-bound holoenzyme was not lost after incubation at 85 ℃ for 100 min. Tt_ASD could oxidize various sugars, including hexoses, pentoses, disaccharides, and polysaccharides, in addition to alcohols. Structural analysis suggested that Tyr156 would be the substratebinding residue. Two mutants, Y156A and Y156K, had impaired activities and affinities for all substrates and completely lost their activities for alcohols. This structural and mutational analysis of Tt_ASD demonstrates the crucial role of Tyr156 in determining substrate specificity.
DOI
http://dx.doi.org/10.1016/j.abb.2016.08.022
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