Abstract
Copper (Cu) is an essential trace element for growth and development and abnormal Cu levels are associated with anemia, metabolic disease and cancer. Evolutionarily conserved from fungi to humans, the high-affinity Cu+ transporter Ctr1 is crucial for both dietary Cu uptake and peripheral distribution, yet the mechanisms for selective permeation of potentially toxic Cu+ ions across cell membranes are unknown. Here we present X-ray crystal structures of Ctr1 from Salmo salar in both Cu+-free and Cu+-bound states, revealing a homo-trimeric Cu+-selective ion channel-like architecture. Two layers of methionine triads form a selectivity filter, coordinating two bound Cu+ ions close to the extracellular entrance. These structures, together with Ctr1 functional characterization, provide a high resolution picture to understand Cu+ import across cellular membranes and suggest therapeutic opportunities for intervention in diseases characterized by inappropriate Cu accumulation.