Biomimetic nicotinamide coenzymes, including nicotinamide mononucleotide (NMN+), have been demonstrated as promising low-cost alternatives to nicotinamide adenine dinucleotide (phosphate) (NAD(P)+) in biocatalysis. Herein, to efficiently regenerate NMNH from NMN+ in vitro powered by biomass sugars, a thermophilic NADP+-dependent glucose 6-phosphate dehydrogenase from Thermotoga maritima (TmG6PDH) was engineered to increase the activity toward NMN+. The catalytic efficiency (kcat/Km) of optimal mutant (TmG6PDH-R7) toward NMN+ increased by 71.7-fold than TmG6PDH-WT. As a result, compared to the wild type, the coenzyme specificity ([kcat/Km]NMN+/[kcat/Km]NADP+) of TmG6PDH-R7 increased by ~2.0×105-fold. The structural analysis revealed that the introduced hydrophobic and bulky residues lead to the formation of a smaller binding pocket, which resulting in a higher affinity for NMN+ with small size than NADP+. Then several in vitro synthetic enzymatic biosystems (ivSEBs) comprising this thermophilic TmG6PDH-R7 and a previously engineered thermophilic 6-phosphogluconate dehydrogenase were constructed. These ivSEBs harnessed the complete oxidation of renewable biomass sugars to facilitate the stoichiometric regeneration of 12 molecules of NMNH from 1 molecule of glucose, thereafter producing various products such as levodione, 2,3-butanediol or bioelectricity, over a wide temperature range. This study could pave the way for using stable and low-cost biomimetic coenzymes in ivSEBs for industrial biomanufacturing.
Keywords: Glucose 6-phosphate dehydrogenase, nicotinamide mononucleotide, Coenzyme engineering, Complete oxidation, Biomass sugars.
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