9.B.27 The DedA or YdjX-Z (DedA) Family
The ubiquitous DedA family (family UPF0043) includes bacterial, archaeal and eukaryotic proteins. The bacterial proteins are of about 200-250 residues with 5 or 6 putative TMSs. They are related to the DedA protein of E. coli (TC# 9.B.27.2.3) and several functionally unchararcterized proteins in eukaryotes (yeasts, plants and animals).YdjX and YdjZ may be involved as dimers in selenite transport (Ledgham et al., 2005). Potential functions of these proteins such as in membrane homeostasis have been summarized by Doerrler et al., (2013). Mutations in DedA proteins exhibit phenotypes such as cell division defects, temperature sensitivity, altered lipid compositions, elevated envelope-related stress responses and loss of the proton motive force. DedA proteins are essential is some bacterial species (Doerrler et al., 2013; Sikdar et al., 2013).
An oxalate-fermenting brown rot fungus, Fomitopsis palustris, secretes large amounts of oxalic acid during wood decay. Secretion of oxalic acid is indispensable for the degradation of wood cell walls. Watanabe et al., (2010) characterized an oxalate transporter, FpOAR, using membrane vesicles of F. palustris. FpOAR (Fomitopsis palustris oxalic acid resistance), from F. palustris by functional screening of yeast transformants with cDNAs grown on oxalic acid-containing plates. FpOAR is predicted to be a membrane protein that possesses six TMSs. A yeast transformant possessing FpOAR (FpOAR-transformant) acquired resistance to oxalic acid and contained less oxalate than the control transformant. FpOAR probably plays a role in wood decay by acting as a secondary transporter responsible for secretion of oxalate by F. palustris.
The DedA/Tvp38 family is a highly conserved and ancient family of membrane proteins with representatives in most sequenced genomes (Doerrler et al., 2013). Recent genetic approaches have revealed important roles for certain bacterial DedA family members in membrane homeostasis. Bacterial DedA family mutants display phenotypes such as cell division defects, temperature sensitivity, altered membrane lipid composition, elevated envelope-related stress responses, and loss of the proton motive force. The DedA family is essential in at least two species of bacteria:Borrelia burgdorferi and Escherichia coli under some conditions. Doerrler et al., (2013) described the phylogenetic distribution of the family and summarized progress toward understanding the functions of DedA proteins.
E. coli can normally grow between pH 5.5 and 9.5 while maintaining a cytoplasmic pH of about 7.6. Under alkaline conditions, bacteria rely upon proton-dependent transporters to maintain a constant cytoplasmic pH. The DedA/Tvp38 protein, YqjA, is critical for E. coli to survive between pH 8.5 and 9.5. YqjA requires sodium and potassium for this function. At low cation concentrations, osmolytes, including sucrose, can facilitate rescue of growth by YqjA at high pH suggesting that YqjA functions as an osmosensing cation-dependent proton transporter (Kumar and Doerrler 2015).