The N-terminus of the human copper transporter 1 (hCTR1) is localized extracellularly, and interacts with itself

We have used indirect immunofluorescense studies and glycosylation-site insertion and deletion mapping to characterize the topology of human copper transporter I (hCTRI), the putative human high-affinity copper-import protein. Both approaches indicated that hCTRI contains three transmembrane domains and that the N-terminus of hCTRI, which contains several putative copper-binding sites, is localized extracellularly, whereas the C-terminus is exposed to the cytosol. Based on previous observations that CTR1 proteins form high-molecular-mass complexes, we investigated directly whether CTR1 proteins interact with themselves. Yeast two-hybrid studies showed that interaction of yeast, mouse, rat and human CTR1 occurs at the sites of their N-terminal domains, and is not dependent on the copper concentration in the growth media. Analysis of deletion constructs indicated that multiple regions in the N-terminus are essential for this self-interaction. In contrast, the N-terminal tail of the presumed low-affinity copper transporter, hCTR2, does not interact with itself. Taken together, these results suggest that CTR1 spans the membrane at least six times, permitting formation of a channel, which is consistent with its proposed role as a copper transporter.