2.A.77 The Cadmium Resistance (CadD) Family
Many currently sequenced proteins comprise the CadD family. Two are close orthologues in two Staphylococcus species that have been reported to function in cadmium resistance, a fourth has been reported to possibly function in quaternary ammonium ion export, and the fourth is a distant ORF in Staphylococcus aureus. These proteins are found in Gram-positive bacteria. Their mode of energy coupling has not been investigated, but a proton antiport mechanism is probable. This family is distantly related to members of the LysE family (TC #2.A.75) and the RhtB family (TC #2.A.76). These three families, which comprise the LysE superfamily, all consist of proteins of similar sizes (about 200 residues) and topologies (6 putative transmembrane α-helical segments, TMSs; 5 experimentally determined TMSs).
The probable reaction catalyzed by these proteins is:
Cationic compound (in) + nH+ (out) Cationic compound (out) + nH+ (in)