A versatile disulfide-driven recycling system for NADP+ with high cofactor turnover number

NADP+-dependent enzymes are important in many biocatalytic processes to generate high-value chemicals for the pharmaceutical and food industry; hence, a costeffective, efficient, and environmentally friendly recycling system for the relatively expensive and only marginally stable enzyme cofactor NADP+ offers significant benefits. NADP+ regeneration schemes have previously been described, but their application is severely limited by the low total turnover numbers (TTN) for the cofactor. Here, we report a glutathione-based recycling system that combines glutaredoxin from E. coli (EcGRX) and the glutathione reductase from S. cerevisiae (ScGR) for NADP+ regeneration. This system employs inexpensive latent organic disulfides such as oxidized cysteine or 2-hydroxyethyl disulfide (HED) as oxidizing agents and allows NADP+ recycling under both aerobic and anaerobic conditions with a TTN in excess of 5 × 105, indicating that each regeneration cycle is 99.9998% selective toward forming the cofactor. Accordingly, for each 1 mol of product generated, less than $0.05 of cofactor is needed. Finally, the EcGRX/ScGR pair is compatible with eight enzymes in the guanosine monophosphate (GMP) biosynthetic pathway, giving the corresponding isotopically labeled nucleotide in high yield. The glutathione-based NADP+ recycling system has potential for biocatalytic applications in academic and industrial settings

Streptavidin as a Scaffold for Light-Induced Long-Lived Charge Separation

Long-lived photo-driven charge separation is demonstrated by assembling a triad on a protein scaffold. For this purpose, a biotinylated triarylamine was added to a Ru II –streptavidin conjugate bearing a methyl viologen electron acceptor covalently linked to the N -terminus of streptavidin. To improve the rate and lifetime of the electron transfer, a negative patch consisting of up to three additional negatively charged amino acids was engineered through mutagenesis close to the biotin-binding pocket of streptavidin. Time-resolved laser spectroscopy revealed that the covalent attachment and the negative patch were beneficial for charge separation within the streptavidin hosted triad; the charge separated state was generated within the duration of the excitation laser pulse, and lifetimes up to 3120 ns could be achieved with the optimized supramolecular triad