Journal
ACS SYNTHETIC BIOLOGY
Volume 8, Issue 2, Pages 264-273Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acssynbio.8b00485
Keywords
redox biosensor; NADH/NAD; high-throughput screening; bacterial physiology; respiratory chain
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Funding
- DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science) [DE-FC02-07ER64494]
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NADH and NAD+ cofactors drive hundreds of biochemical reactions, and their ratio is a key metabolic marker of cellular state. Traditional assays to measure the NADH/NAD+ ratio is laborious, prone to inaccuracies, and not suitable for high-throughput screening. We report a genetically encoded ratiometric biosensor for NADH/NAD+ based on redox-responsive bacterial transcription factor Rex that overcomes these limitations. We engineered a Rex-regulated E. coli promoter with improved biosensor characteristics by tuning the affinity of Rex and the operator site. Since NADH is oxidized during aerobic respiration, we used the biosensor-reporter to investigate the effect of removing respiratory chain enzymes on NADH/NAD+ ratio during aerobiosis. We found that the NADH/NAD+ signal increased in five of the nine mutants by over 3-fold compared to wildtype, including an NADH dehydrogenase double mutant with 6-fold elevation. We also found that among several common carbon sources, E. coli grown on acetate exhibited higher NADH/NAD+ compared to E. coli grown on glucose. As a proof-of-concept for high-throughput redox screening, we were able to enrich high NADH mutants present at 1 in 10000 among wildtype cells by biosensor-guided pooled screen. Thus, our Rex biosensor-reporter enables facile, noninvasive, high-throughput redox measurement to understand and engineer redox metabolism.
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