Direct Comparison of Manganese Detoxification/Efflux Proteins and Molecular Characterization of ZnT10 Protein as a Manganese Transporter

Abstract

Manganese (Mn) homeostasis involves coordinated regulation of specific proteins involved in Mn influx and efflux. However, the proteins that are involved in detoxification/efflux have not been completely resolved, nor has the basis by which they select their metal substrate. Here, we compared six proteins, which were reported to be involved in Mn detoxification/efflux, by evaluating their ability to reduce Mn toxicity in chicken DT40 cells, finding that human ZnT10 (hZnT10) was the most significant contributor. A domain swapping and substitution analysis between hZnT10 and a zinc-specific transporter hZnT1 showed that residue N43, which corresponds to the His residue constituting the potential intramembranous zinc coordination site in other ZnT transporters, is necessary to impart hZnT10's unique Mn mobilization activity; residues C52 and L242 in transmembrane domains II and V play a subtler role in controlling the metal specificity of hZnT10. Interestingly, the H->N reversion mutant in hZnT1 conferred Mn transport activity and loss of zinc transport activity. These results provide important information about Mn detoxification/efflux mechanisms in vertebrate cells as well as the molecular characterization of hZnT10 as a Mn transporter.