2.A.79 The Threonine/Serine Exporter (ThrE) Family
The first member of the ThrE family to be characterized was the ThrE protein of Corynebacterium glutamicum (Simic et al., 2002). This protein (489aas) exhibits 10 putative TMSs and catalyzes the pmf-dependent efflux of threonine and serine (Kruse et al., 2002). It has close homologues in Mycobacterium tuberculosis (Rv 3737; 529aas; pirB70798) and Strepomyces coelicolor (578aas; pirT36336. However more distant homologues, some of which consist of 'spliced' two-component systems, are also found in E. coli, Vibrio cholera, Xylella fastidiosa, Saccharomyces cerevisiae, Schizosaccharomyces pombe and Methanobacterium thermoautotrophicum. Thus, members of the ThrE family are diverse in sequence and are ubiquitous, being found in bacteria, archaea and eukaryotes (Eggeling and Sahm, 2003; Yen et al., 2002). Other characterized members of this family catalyze succinate (and probably other dicarboxylate) transport (export; see TC# 2.A.79.2.1).
The transport reaction catalyzed by ThrE of E. coli (TC# 2.A.79.1.1) is:
threonine or serine (in) + H+ (out) ⇌ threonine or serine (out) + H+ (in)
That for YjjPB of E. coli (TC# 2.A.79.2.1) is:
dicarboxylate (succinate, and probably malate and fumarate) (in) + H+ (out) ⇌ dicarboxylate (out) + H+ (in).