2.A.102 The 4-Toluene Sulfonate Uptake Permease (TSUP) Family
The TSUP family is also referred to as the TauE/SafE/YfcA/DUF81/COG0730 Family. Although its members have not been rigorously characterized, evidence is available that at least some members function in the transport of sulfur containing organic compounds. These include sulfolactate which may be exported by the TauE protein of Cupriavidus necator (Weinitschke et al. 2007; Mayer et al. 2012) and sulfoacetate which may be exported by the SafE1 protein of Neptuniibacter caesariensis (Krejcík et al. 2008). Another member of the TSUP family, TsaS of Comamonas testosteroni, has been reported to function in the uptake of 4-toluene sulfonate (Mampel et al. 2004). None of these functional assignments can be considered to be certain.
The TSUP family has been characterized using bioinformatic approaches. Shlykov et al. 2012; showed that prokaryotic members of the family outnumber the eukaryotic members substantially, and in prokaryotes, but not eukaryotes, extensive lateral gene transfer occurred during family evolution. Despite unequal representation, homologues from the three taxonomic domains of life share well-conserved motifs. A prototypical eight TMS topology apparently arose by intragenic duplication of a four transmembrane segment (TMS) unit. Possibly, a two TMS α-helical hairpin structure was the precursor of the 4 TMS repeat unit. Genome context analyses confirmed the proposal of a sulfur-based compound transport role for many TSUP homologues, but functional outliers appear to be prevalent as well (Shlykov et al. 2012). The TSUP is an established member of the Transporter/Opsin/G protein-coupled receptor (TOG) superfamily (Yee et al. 2013).