A mediator-adapted diaphorase variant for a glucose dehydrogenase–diaphorase biocatalytic system

• Published in: Biosensors & bioelectronics 2010-10, Vol.26 (2), p.452-457
• Main Authors: Sugiyama, Taiki, Goto, Yoshio, Matsumoto, Ryuhei, Sakai, Hideki, Tokita, Yuichi, Hatazawa, Tsuyonobu
• Format: Article
• Language: English
• Subjects: Bioconversions. Hemisynthesis; Bioelectric Energy Sources - microbiology; Biofuel cell; Biological and medical sciences; Biotechnology; Catalysis; Diaphorase; Dihydrolipoamide Dehydrogenase - chemistry; Directed molecular evolution method; Equipment Design; Equipment Failure Analysis; Escherichia coli - physiology; Fundamental and applied biological sciences. Psychology; General aspects; Genetic Variation; Glucose 1-Dehydrogenase - chemistry; Immobilization techniques; Mediator; Methods. Procedures. Technologies; Mutation; Protein engineering; Protein immobilization
• ISSN: 0956-5663; 1873-4235
• DOI: 10.1016/j.bios.2010.07.092

Biofuel cell is an energy conversion device of the next generation which enables use of safer and higher energy-density fuels such as glucose. We have been developing a biofuel cell that comprises the three enzymes: glucose dehydrogenase (GDH) and diaphorase (DI) on anode, and bilirubin oxidase (BOD) on cathode. In this work, we have developed a DI variant suitable for our biofuel cell by using directed molecular evolution method. A gene library of DI variants was constructed by using error-prone PCR and the variant proteins were expressed in an Escherichia coli system. 8000 isolated variants have been screened with activity against 2-amino-1,4-naphthoquinone (ANQ), and 10 of them have been qualified which were then purified and examined their activities against ANQ. A highest activity was observed in G122D variant of which glycine residue at position 122 is substituted to aspartate. Enzymatic kinetic analyses show that K M for ANQ in G122D is 1/3 of that in wild type (G122D: 356 μM, wild type: 1.08 mM), whereas k cat and K M for NADH is almost the same, clearly showing that G122D mutation has given DI an improvement in enzymatic activity at lower ANQ concentration. The effect of this mutation was considered electrochemically in solution and in immobilized layer. The results show that G122D variant DI gave a higher current at lower ANQ concentration in solution, as well as in immobilized condition where GDH is co-immobilized within.