ATP regeneration by a single polyphosphate kinase powers multigram-scale aldehyde synthesis in vitro

Abstract

ATP recycling systems are required to avoid the addition of stoichiometric quantities of cofactor and facilitate industrial implementation of ATP-dependent enzymes. One factor that limits the biocatalytic application of these enzymes is the lack of a scalable AMP to ATP regeneration system. Whole-cells or a combination of purified enzymes are often exploited for ATP regeneration from AMP, whereas cell free systems comprising a single crude enzyme preparation would be preferred. To establish such a system, we focussed on polyphosphate kinases (PPKs) to find a single enzyme that could be used to power ATP-consuming reactions. Screening of some previously reported PPKs revealed limitations of these biocatalysts for scale-up purposes. As such, a panel of novel putative PPK2-III enzymes was constructed and compared to characterised enzymes belonging to the same class. Multidimensional small-scale screening revealed that PPK12 (from an unclassified Erysipelotrichaceae bacterium) displays enhanced expression levels, ATP formation rates, polyphosphate tolerance and stability under a variety of harsh conditions. The carboxylic acid reductase (CAR) catalysed reduction of carboxylates to aldehydes was chosen as a model reaction to test the applicability of PPK12 as a bifunctional biocatalyst for ATP regeneration from AMP. The implementation of the identified ATP-recycling enzyme provided the first example of cell free multigram-scale aldehyde synthesis employing enzymes and a single PPK2-III, paving the way for affordable scalable ATP regeneration technologies.