Characterization of a transcriptional regulator PtxS from Pseudomonas plecoglossicida for regulating 2-ketogluconic acid metabolism.

Homologs of PtxS are ubiquitous transcriptional regulators controlling the expression of the glucose dehydrogenase and kgu operon to globally regulate the 2-ketogluconic acid (2KGA) metabolism in Pseudomonas. In the present study, a PtxS from a 2KGA industrial producer Pseudomonas plecoglossicida JUIM01 (PpPtxS) was heterologously expressed in E. coli BL21(DE3), then structurally and functionally characterized. The obtained results showed that PpPtxS was a 36.65-kDa LacI-family transcriptional regulator. 2KGA was the sole effector of PpPtxS. Glucose negatively affected the molecular binding of PpPtxS and 2KGA, and gluconic acid inhibited the PpPtxS-2KGA binding reaction. PpPtxS in water solution mainly existed as a dimer and bound to two molecules of 2KGA. The effector 2KGA mainly bound to the region close to the C-terminal of PpPtxS by interacting with the 299th to the 301st amino acids (Ala, Gln, Pro, Thr, Glu and Arg). PpPtxS specifically recognized and bound to a 14-bp palindrome sequence (5'-TGAAACCGGTTTCA-3') due to its conserved HTH motif at the N-terminal. The characterization of PpPtxS in this study would provide a theoretical guidance for the industrial production of 2KGA.