Solution Structure of the Yeast Copper Transporter Domain Ccc2a in the Apo and Cu(I)-loaded States

Ccc2 is an intracellular copper transporter in Saccharomyces cerevisiae and is a physiological target of the copper chaperone Atxl. Here we describe the solution structure of the first N-terminal MTCXXC metal-binding domain, Ccc2a, both in the presence and absence of Cu(I). For Cu(I)-Ccc2a, 1944 meaningful nuclear Overhauser effects were used to obtain a family of 35 structures with root mean square deviation to the average structure of 0.36 ± 0.06 ̊ for the backbone and 0.79 ± 0.05 ̊ for the heavy atoms. For apo-Ccc2a, 1970 meaningful nuclear Overhauser effects have been used with 35 ³J_HNHαto obtain a family of 35 structures with root mean square deviation to the average structure of 0.38 ± 0.06 ̊ for the backbone and 0.82 ± 0.07 ̊ for the heavy atoms. The protein exhibits a βαββαβ ,ferrodoxin-like fold similar to that of its target Atxl and that of a human counterpart, the fourth metal-binding domain of the Menkes protein. The overall fold remains unchanged upon copper loading, but the copper-binding site itself becomes less disordered. The helical context of the copper-binding site, and the copper-induced conformational changes in Ccc2a differ from those in Atxl. Ccc2a presents a conserved acidic surface which complements the basic surface of Atxl and a hydrophobic surface. These results open new mechanistic aspects of copper transporter domains with physiological copper donor and acceptor proteins.