Browsing by Author "Chen, Hui"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Coenzyme Engineering of a Hyperthermophilic 6-Phosphogluconate Dehydrogenase from NADP(+) to NAD(+) with Its Application to Biobatteries
    Chen, Hui; Zhu, Zhiguang; Huang, Rui; Zhang, Y. H. Percival (Nature Publishing Group, 2016-11-02)
    Engineering the coenzyme specificity of redox enzymes plays an important role in metabolic engineering, synthetic biology, and biocatalysis, but it has rarely been applied to bioelectrochemistry. Here we develop a rational design strategy to change the coenzyme specificity of 6-phosphogluconate dehydrogenase (6PGDH) from a hyperthermophilic bacterium Thermotoga maritima from its natural coenzyme NADP(+) to NAD(+). Through amino acid-sequence alignment of NADP(+)-and NAD(+)-preferred 6PGDH enzymes and computer-aided substrate-coenzyme docking, the key amino acid residues responsible for binding the phosphate group of NADP(+) were identified. Four mutants were obtained via site-directed mutagenesis. The best mutant N32E/R33I/T34I exhibited a x 6.4 x 10(4)-fold reversal of the coenzyme selectivity from NADP(+) to NAD(+). The maximum power density and current density of the biobattery catalyzed by the mutant were 0.135 mW cm(-2) and 0.255 mA cm(-2), similar to 25% higher than those obtained from the wide-type 6PGDH-based biobattery at the room temperature. By using this 6PGDH mutant, the optimal temperature of running the biobattery was as high as 65 degrees C, leading to a high power density of 1.75 mW cm(-2). This study demonstrates coenzyme engineering of a hyperthermophilic 6PGDH and its application to high-temperature biobatteries.
  • Thumbnail Image
    High-Throughput Screening of Coenzyme Preference Change of Thermophilic 6-Phosphogluconate Dehydrogenase from NADP⁺ to NAD⁺
    Huang, Rui; Chen, Hui; Zhong, Chao; Kim, Jae Eung; Zhang, Yi-Heng Percival (Nature, 2016-09-02)
    Coenzyme engineering that changes NAD(P) selectivity of redox enzymes is an important tool in metabolic engineering, synthetic biology, and biocatalysis. Here we developed a high throughput screening method to identify mutants of 6-phosphogluconate dehydrogenase (6PGDH) from a thermophilic bacterium Moorella thermoacetica with reversed coenzyme selectivity from NADP⁺ to NAD⁺. Colonies of a 6PGDH mutant library growing on the agar plates were treated by heat to minimize the background noise, that is, the deactivation of intracellular dehydrogenases, degradation of inherent NAD(P)H, and disruption of cell membrane. The melted agarose solution containing a redox dye tetranitroblue tetrazolium (TNBT), phenazine methosulfate (PMS), NAD⁺, and 6-phosphogluconate was carefully poured on colonies, forming a second semi-solid layer. More active 6PGDH mutants were examined via an enzyme-linked TNBT-PMS colorimetric assay. Positive mutants were recovered by direct extraction of plasmid from dead cell colonies followed by plasmid transformation into E. coli TOP10. By utilizing this double-layer screening method, six positive mutants were obtained from two-round saturation mutagenesis. The best mutant 6PGDH A30D/R31I/T32I exhibited a 4,278-fold reversal of coenzyme selectivity from NADP⁺ to NAD⁺. This screening method could be widely used to detect numerous redox enzymes, particularly for thermophilic ones, which can generate NAD(P)H reacted with the redox dye TNBT.