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 together initially comprised 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 superfamily has since been expanded. Bacterial responses and their mechanisms of bacterial metallogenic detoxification under high concentrations of heavy metals have been studied (Li et al. 2022).
The probable reaction catalyzed by these proteins is:
Cationic compound (in) + nH+ (out) Cationic compound (out) + nH+ (in)