The redox active metal copper is an essential cofactor in critical biological processes such as respiration, iron transport, oxidative stress protection, hormone production, and pigmentation. A widely conserved family of high-affinity copper transport proteins (Ctr proteins) mediates copper uptake at the plasma membrane. A series of clustered methionine residues in the hydrophilic extracellular domain, and an MXXXM motif in the second transmembrane domain, are important for copper uptake. These methionine probably coordinate copper during the process of metal transport.

1: Biochemical and genetic analyses of yeast and human high-affinity copper transporters suggest a conserved mechanism for copper uptake. Puig S, Lee J, Lau M, Thiele DJ; J Biol Chem 2002;0:0-0. PMID:11983704