Involved in the regulation of 2-ketogluconic acid metabolism via the control of the expression of the kgu operon (PubMed:33529626). Binds directly to a 14-bp palindrome sequence via its conserved HTH motif (PubMed:33529626). 2-ketogluconate acts as a molecular effector and causes dissociation of PtxS from its target promoter (PubMed:33529626). Glucose negatively affects the molecular binding of PtxS and 2KGA, and gluconic acid inhibits the PtxS-2KGA binding reaction (PubMed:33529626). Homodimer. Contains an N-terminal helix-turn-helix DNA-binding domain and a C-terminal domain that binds the effector.