This family includes four different proteins from E. coli alone. One of them, YdgG or TqsA, has been shown to mediate transport of the quorum-sensing signal autoinducer 2 (AI-2). It is not clear if TqsA enhances secretion of AI-2 or inhibits AI-2 uptake. By altering the intracellular concentration of AI-2, TqsA affects gene expression in biofilms and biofilm formation. TsqA belongs to the AI-2 exporter (AI-2E) superfamily.
Jiyao W et al.(2023). "The conserved domain database in 2023.",