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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 associated with 2.A.79 family:

Bendezú, F.O. and P.A. de Boer. (2008). Conditional lethality, division defects, membrane involution, and endocytosis in mre and mrd shape mutants of Escherichia coli. J. Bacteriol. 190: 1792-1811. 17993535
Eggeling, L. and H. Sahm. (2003). New ubiquitous translocators: amino acid export by Corynebacterium glutamicum and Escherichia coli. Arch. Microbiol. 180: 155-160. 12879215
Fukui, K., K. Nanatani, Y. Hara, M. Tokura, and K. Abe. (2018). Identification of EayjjPB encoding a dicarboxylate transporter important for succinate production under aerobic and anaerobic conditions in Enterobacter aerogenes. J Biosci Bioeng 125: 505-512. 29395959
Fukui, K., K. Nanatani, Y. Hara, S. Yamakami, D. Yahagi, A. Chinen, M. Tokura, and K. Abe. (2017). Escherichia coli yjjPB genes encode a succinate transporter important for succinate production. Biosci. Biotechnol. Biochem. 81: 1837-1844. 28673128
Kruse, D., R. Krämer, L. Eggeling, M. Rieping, W. Pfefferle, J.H. Tchieu, Y.J. Chung, M.H. Jr Saier, and A. Burkovski. (2002). Influence of threonine exporters on threonine production in Escherichia coli. Appl. Microbiol. Biotechnol. 59: 205-210. 12111147
Leaver, M. and J. Errington. (2005). Roles for MreC and MreD proteins in helical growth of the cylindrical cell wall in Bacillus subtilis. Mol. Microbiol. 57: 1196-1209. 16101995
Simic, P., J. Willuhn, H. Sahm, and L. Eggeling. (2002). Identification of glyA (encoding serine hydroxymethyltransferase) and its use together with the exporter ThrE to increase L-threonine accumulation by Corynebacterium glutamicum. Appl. Environ. Microbiol. 68: 3321-3327. 12089010
Southworth, T.W., A.A. Guffanti, A. Moir, and T.A. Krulwich. (2001). GerN, an endospore germination protein of Bacillus cereus, is an Na+/H+-K+ antiporter. J. Bacteriol. 183: 5896-5903. 11566988
Stratmann, T., S. Madhusudan, and K. Schnetz. (2008). Regulation of the yjjQ-bglJ operon, encoding LuxR-type transcription factors, and the divergent yjjP gene by H-NS and LeuO. J. Bacteriol. 190: 926-935. 18055596
Yen, M.R., Y.H. Tseng, P. Simic, H. Sahm, L. Eggeling, and M.H. Saier, Jr. (2002). The ubiquitous ThrE family of putative transmembrane amino acid efflux transporters. Res. Microbiol. 153: 19-25. 11881894