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).
References:
Threonine/Serine exporter, ThrE (10 TMSs; DUF1212; Eggeling & Sahm, 2003)
Bacteria, archaea and eukarya
ThrE of Corynebacterium glutamicum (Q79VD1)
Pheromone-regulated membrane protein 10 of 1150 aas and 10 - 12 TMSs. CDD shows YjjP (DUF1212) and ProP (MFS) domains overlapping in the C-terminal transmembrane region. The N-terminal soluble domains shows sequence similarity to Insecticidal Vegetative Protein-3 Family (TC# 1.C.105.2.7; e-8).
Pheromone-regulated protein 10 of Candida albicans (Yeast)
ThrE homologue
Proteobacteria
ThrE homologue of Myxococcus xanthus
ThrE homologue
Actinobacterium
ThrE homologue of Propionibacterium acnes
PF06738 family protein
Fusobacteria
PF06738 family protein of Fusobacterium nucleatum
Putative 2-component glycine/alanine porter
Spirochaetes
Putative gly/ala porter of Treponema denticola
Uncharacterized protein of 147 aas and 5 TMSs.
UP of Clostridium clariflavum
Uncharacterized protein of 142 aas
UP of Paenibacillus sp. FSL H8-237
Uncharacterized protein of 430 aas and 10 TMSs in a 5 + 5 spatial arrangement.
UP of Mobilicoccus pelagius
Uncharacterized protein of 606 aas and 9 or 10 TMSs
UP of Mucor circinelloides (Mucormycosis agent) (Calyptromyces circinelloides)
YjjP (P0ADD5)/YjjB (P0ADD2) are of 256 aas and 5 TMSs; (DUF1212) and of 157 aas and 4 or 5 TMSs, respectively. yjjPB gene expression is regulated by HNS (a repressor) and LeuO (which antagonizes the repressive activity of HNS) (Stratmann et al. 2008). These proteins are encoded within a two gene operon, yjjPB, which encodes a two component dicarboxylate (succinate, fumarate and malate) transporter that has been shown to catalyze succinate efflux (Fukui et al. 2017). It is similar to the dicarboxylate/succinate transporter, YjjPB, of Enterobacter aerogenes (Fukui et al. 2018).
Bacteria
YjjP/YjjB of E.coli (P0ADD5/P0ADD2)
DUF1212 homologue
Proteobacteria
DUF1212 homologue of Rhodopseudomonas palustris