Involved in the degradation of phospho-AI-2, thereby terminating induction of the lsr operon and closing the AI-2 signaling cycle. Catalyzes the conversion of (4S)-4-hydroxy-5-phosphonooxypentane-2,3-dione (P-DPD) to 3-hydroxy-5-phosphonooxypentane-2,4-dione (P-HPD). (2S)-2-hydroxy-3,4-dioxopentyl phosphate = 3-hydroxy-2,4-dioxopentyl phosphate Homodimer. In the absence of AI-2, repressed by LsrR. Induced by AI-2, via release of the LsrR repressor. In the absence of glucose, induced by cAMP-CRP by direct binding to the upstream region of the lsr promoter. Belongs to the LsrG family.