Bacterial Autoinducer-2 (AI-2) and its precursor, 4,5-dihydroxy-2,3-pentanedione (DPD), mediate the quorum sensing 2 system. DPD is synthesized from S-ribosylhomocysteine (SRH) by the LuxS enzyme, which is found in both E. coli and S. typhimurium. In E. coli and most pathogenic bacteria, DPD undergoes spontaneous transformations, including cyclization to form (2R,4S)-2-methyl-2,4-dihydroxydihydrofuran-3-one and hydration to the final autoinducer, (2R,4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (AI-2). This product is then released from the cell through the AI-2 transporter (TqsA). As the level of AI-2 increases, other cells detect it and import it through the autoinducer-2 ABC transporter (LsrACDB). Inside the cells, AI-2 is degraded by phosphorylation, followed by isomerization to P-HPD. Finally, the acetyl group of P-HPD is transferred to coenzyme A, and dihydroxyacetone phosphate is released. Both DPD and AI-2 play critical roles in quorum sensing, allowing bacteria to coordinate gene expression in response to population density.

Quorum sensing - Autoinducer-2 Biosynthesis References