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 [1]. TsqA belongs to the AI-2 exporter (AI-2E) superfamily [2].

1: YdgG (TqsA) controls biofilm formation in Escherichia coli K-12 through autoinducer 2 transport. Herzberg M, Kaye IK, Peti W, Wood TK; J Bacteriol. 2006;188:587-598. PMID:16385049

2: The autoinducer-2 exporter superfamily. Rettner RE, Saier MH Jr; J Mol Microbiol Biotechnol. 2010;18:195-205. PMID:20559013