2.A.86 The Autoinducer-2 Exporter (AI-2E) Family (formerly the PerM Family, TC #9.B.22)
The AI-2E family (UPF0118) is a large family of prokaryotic proteins derived from a variety of bacteria and archaea. Those examined are about 350 residues in length, and the couple that have been examined exhibit 7 putative transmembrane α-helical spanners (TMSs) (Rettner and Saier, 2010). E. coli, B. subtilis and several other prokaryotes have multiple paralogues encoded within their genomes. Herzberg et al. (2006) have presented strong evidence for a role of a AI-2E family homologue, YdgG (renamed TqsA), as an exporter of the E. coli autoinducer-2 (AI-2) (Camilli and Bassler, 2006; Chen et al., 2002). AT-2 is a proposed signalling molecule for interspecies communication in bacteria. It is a furanosyl borate diester (Chen et al., 2002). It is induced in Bacillus subtilis by exposure to rice seedlings (Xie et al. 2015).
More recently, it has been reported that this family includes a member of the UPF0118 family (which is the former designation for the AI-2E family), and this transmembrane protein with 7 TMSs, exhibits pH-dependent Na+ or Li+/H+ antiport activity. Phylogenetic analyses were reported (Dong et al. 2017). Thus, it appears that different members of the family may have very different transport functions.
The transport reactions catalyzed by membeers of the AI-2E family are:
AI-2 (in) ⇌ AI-2 (out)
Na+ or Li+ (out) + H+ (in) → Na+ or Li+ (in) + H+ (out)