NADPH-generating systems in bacteria and archaea.

Sebastiaan K Spaans,John Van Der Oost,Servã© W M Kengen,Ruud A Weusthuis

doi:10.3389/fmicb.2015.00742

Abstract

Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is an essential electron donor in all organisms. It provides the reducing power that drives numerous anabolic reactions, including those responsible for the biosynthesis of all major cell components and many products in biotechnology. The efficient synthesis of many of these products, however, is limited by the rate of NADPH regeneration. Hence, a thorough understanding of the reactions involved in the generation of NADPH is required to increase its turnover through rational strain improvement. Traditionally, the main engineering targets for increasing NADPH availability have included the dehydrogenase reactions of the oxidative pentose phosphate pathway and the isocitrate dehydrogenase step of the tricarboxylic acid (TCA) cycle. However, the importance of alternative NADPH-generating reactions has recently become evident. In the current review, the major canonical and non-canonical reactions involved in the production and regeneration of NADPH in prokaryotes are described, and their key enzymes are discussed. In addition, an overview of how different enzymes have been applied to increase NADPH availability and thereby enhance productivity is provided.

Highlights

Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is an essential electron donor in all eukaryotes, bacteria, and archaea
In wildtype Escherichia coli aerobically grown in chemostats under glucose- or ammonia-limited conditions, the IDH reaction was the major producer of NADPH, accounting for more than 60% of the total NADPH production (Hua et al, 2003)
In prokaryotes that contain alternative GAP oxidation enzymes, such as NAD+-GAPDH, glyceraldehyde 3phosphate dehydrogenase (GAPN), or GAP:ferredoxin oxidoreductase (GAPOR) (Figure 4), NADP+-GAPDH is primarily involved in gluconeogenesis and does not appear to play a role in generating NADPH (Schäfer and Schönheit, 1993; Koksharova et al, 1998; Fillinger et al, 2000; Brunner et al, 2001; Matsubara et al, 2011; Ito et al, 2012)

Summary

Introduction

Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is an essential electron donor in all eukaryotes, bacteria, and archaea. With the possibility of engineering microbial metabolism to facilitate product formation, it became clear that NADPH availability remains a major hurdle in the efficient generation of many products These products range from medicinal compounds (Chemler et al, 2010; Siedler et al, 2011; Zhao et al, 2011) and (essential) amino acids (Becker et al, 2007; Papagianni, 2012) to molecules used as biofuels (Asadollahi et al, 2009; Kim et al, 2011; Peralta-Yahya et al, 2012) and building blocks for biodegradable plastic (Kabir and Shimizu, 2003). In addition to its redox function, NAD+ serves as a substrate for mono- and poly-ADP ribosylation, participates in histone deacetylation, and contributes to the production of the signaling molecule cyclic ADP-ribose Most of these reactions have been characterized in eukaryotes, but the ribosylation reactions play a role in toxin production by pathogenic bacteria (Ziegler, 2000; Pollak et al, 2007). Two principal NAD+ biosynthesis pathways have been characterized: (1) the de novo pathway and TABLE 1 | Overview of major canonical and non-canonical NADPH-generating enzymes

FAD or FMN no

Systems for NADPH Generation

Isocitrate Dehydrogenase

Desulfovibrio fructosovorans and the hyperthermophilic archaea

Findings

Final Remarks and Conclusion