Molecular cloning, expression in Escherichia coli and structural-functional analysis of a pyruvate kinase from Pyrobaculum calidifontis

Application of recombinant human pyruvate kinase in recombinase polymerase amplification

Recombinase polymerase amplification (RPA) is an isothermal DNA amplification reaction at around 41°C using recombinase (Rec), single-stranded DNA-binding protein (SSB), strand-displacing DNA polymerase (Pol), and an ATP-regenerating enzyme. In this study, we attempted to use pyruvate kinase instead of creatine kinase (CK) that has been consistently used as an ATP-regenerating enzyme in RPA. Human pyruvate kinase M1 (PKM) was expressed in Escherichia coli and purified from the cells. RPA with PKM was performed at 41°C with the in vitro synthesized urease subunit β (ureB) DNA from Ureaplasma parvum serovar 3 as a standard DNA. The optimal concentrations of PKM and phosphoenolpyruvate were 20 ng/μL and 10 mM, respectively. The RPA reaction with PKM was more sensitive than that with CK. PKM exhibited higher thermostability than CK, suggesting that the RPA reagents with PKM are preferable to those with CK for onsite use.

Investigation of enzymatic quality and quantity using pyridoxal 5'-phosphate (PLP) regeneration system as a decoy in Escherichia coli

Pyridoxal 5'-phosphate (PLP), an essential cofactor for multiple enzymes, was used as a protein decoy to prompt enzyme expression and activity for the first time. The best chassis, denoted as WJK, was developed using a pyridoxal kinase (PdxK) and integrated at the HK022 phage attack site of Escherichia coli W3110. When compared with the original strain, the amount and activity of lysine decarboxylase (CadA) in WJK were significantly increased by 100 % and 120 %, respectively. When supplementary nineteen amino acids as second carbon source, cell growth and protein trade-off were observed. The transcriptional levels of genes from glycolysis to TCA cycle, adhE, argH and gdhA were dominating and redirected more flux into α-ketoglutarate, thus facilitated cell growth. Stepwise improvement was conducted with pyridoxal and nitrogen-rich medium; hence, CadA activity was increased to 60 g-cadaverine/g-dry cell weight/h. By reutilizing the whole-cell biocatalysts in two repeated reactions with the supplementation of fresh cells, a total cadaverine of 576 g/L was obtained even without additional PLP. Notably, PLP decoy augment the enzymatic activities of 5-aminolevulinic acid synthase and glutamate/lysine/arginine decarboxylases by over 100 %. Finally, a conserved PLP-binding pocket, Ser-His-Lys, was identified as a vital PLP sponge site that simultaneously improved protein quality and quantity.