High-affinity, saturable copper transporter involved in dietary copper uptake. Homotrimer. Localizes to the apical membrane in intestinal epithelial cells. O-Glycosylation at Thr-27 protects from proteolytic cleavage in the N-terminal extracellular domain. Belongs to the copper transporter (Ctr) (TC 1.A.56) family. SLC31A subfamily.