9.A.43 The Cadmium Tolerance Efflux Pump (CTEP) Family
Cadmium (Cd) causes the generation of reactive oxygen species (ROS), which in turn causes cell damage. Kim et al (2008) isolated a novel gene from a wheat root cDNA library, which conferred Cd2+-specific tolerance when expressed in Saccharomyces cerevisiae. The gene, called TaTM20, for Triticum aestivum transmembrane 20, encodes a hydrophobic polypeptide of 889 amino acids, containing 20 transmembrane domains arranged as a 5-fold internal repeating unit of 4 transmembrane domains each. Expression of TaTM20 in yeast cells stimulated Cd2+ efflux resulting in a decrease in the content of yeast intracellular Cd2+. TaTM20-induced Cd2+ tolerance was maintained in yeast even under conditions of reduced glutathione (GSH). Thus, TaTM20 enhances Cd2+ tolerance in yeast through the stimulation of Cd2+ efflux from the cell, partially independent of GSH. Treatment of wheat seedlings with Cd2+ induced their expression of TaTM20, decreasing subsequent root Cd2+ accumulation and suggesting a possible role for TaTM20 in Cd2+ tolerance in wheat (Kim et al. 2008).
The proteins of this family seem to be exclusively from plants, but many of them do not have the 4 TMS repeats. They instead each have a single 4 TMS unit, usually at their C-termini. It is possible that these proteins are related to the bacterial protein in TC family 9.B.257, but this has not been examined carefully.
Cd2+ tolerance factor, TaTM20, a hydrophobic polypeptide of 889 amino acids, containing 20 transmembrane domains arranged as a 5-fold internal repeating unit of 4 transmembrane domains each (Kim et al., 2008). The 4 TMS repeat has been referred to as the pfam13962 or PGG domain. The PGG domain is named for the conserved sequence motif found at the start of the domain.The protein appears to function as a Cd2+ exporter, possibly using the pmf and functioning as a secondary carrier (see family description).
Cd2+ tolerance factor of Triticum aestivum (Q2MJU2)
Uncharacterized protein of 464 aas and 4 C-terminal TMSs (residues 300 - 450). The N-terminal domain is an ankyrin domain, showing extensive similarity to members of TC families 1.A.4 (TRP-CC) and 8.A.28 (Ankyrin domain proteins). The C-terminal TMSs are in a 1 + 3 TMS arrangement as is true of other members of the TC# 9.A.43 (CTEP) family.
UP of Acer yangbiense
Uncharacterized protein of 219 aas and 4 C-terminal TMSs.
UP of Panicum miliaceum
Uncharacterized ankyrin repeat family protein of 574 aas and 4 C-terminal TMSs. Other TMSs may be present in the large N-terminal ankyrin domain. This protein, and many others, share domains with 9.A.43 and 8.A.28, due to the ankyrin domains.
Ankyrin repeat protein of Arabidopsis thaliana
Uncharacterized protein of 222 aas and 4 C-terminal TMSs.
UP of Brachypodium distachyon
The accelerated cell death 6, ACD6, of 670 aas and 5 C-terminal TMSs. It is an activator of the defense response against virulent pathogens, including bacteria, fungi and oomycetes, that acts in a positive feedback loop with the defense signal salicylic acid (SA) (Lu et al. 2009).It regulates the salicylic acid (SA) signaling pathway leading to cell death and modulating cell fate (e.g. cell enlargement and/or cell division) (Lu et al. 2003). In response to SA signaling, it triggers the accumulation of FLS2 at the plasma membrane, thus priming defenses (Zhang et al. 2014). Irt it is involved in SA-dependent freezing signaling and tolerance (Miura and Ohta 2010). Information exchange between the ankyrin and transmembrane domains may be involved in activating defense signaling (Lu et al. 2005).
ACD6 of Arabidopsis thaliana
Uncharacterized ankyrin domain-containing protein of 210 aas and 4 TMSs. Overlapping regions of homology with other members of this family as well as with TC# 9.B.257 seems likely but have not been demonstrated.
UP of Arachis duranensis
Uncharacterized protein of 175 aas and 4 TMSs.
UP of Glycine max (Soybean) (Glycine hispida)
Uncharacterized protein of 459 aas and 4 C-terminal TMSs.
UP of Solanum lycopersicum (Tomato) (Lycopersicon esculentum)
Uncharacterized protein of 179 aas and 4 TMSs.
UP of Populus trichocarpa (Western balsam poplar) (Populus balsamifera subsp. trichocarpa)
Embryogeneis transmembrane protein of 275 aas and 4 TMSs
E-TMP of Zea mays (Maize)
Embryogenesis transmembrane protein of 1276 aas and 20 TMSs, E-TMP or TM20. It is present in differentiating provascular cells in rice and maize embryos, and has a polarized distribution within the cell in the more differentiated stages of development, and modifieds transport properties when injected into frog oocytes (Jahrmann et al. 2005).
E-TMP of Oryza sativa subsp. japonica (Rice)
Embryogenesis transmembrane protein of 275 aas and 6 TMSs
E-TMP of Oryza sativa subsp. japonica (Rice)
Uncharacterized protein of 227 aas and 5 TMSs.
UP of Triticum urartu (Red wild einkorn) (Crithodium urartu)
Embryogenesis transmembrane protein Dek34 or TM20 of 1,389 aas and 21 TMSs in a 1 + 4 + 4 + 4 + 4 + 4 TMS arrangement, where each 4 TMS repeat unit has a 1 + 3 TMS arrangement. TM20 is present in differentiating provascular cells in maize embryos. The protein has a polarized distribution within the cell in the more differentiated stages of development. Xenopus laevis oocytes microinjected with TM20 appear to show modified transport activities across the plasma membrane (Jahrmann et al. 2005).
TM20 of Zea mays (Maize)