Structure and interactions of the C-terminal metal binding domain of Archaeoglobus fulgidus CopA

The Cu⁺-ATPase CopA from Archaeoglobus fulgidus belongs to the P_1B family of the P-type ATPases. These integral membrane proteins couple the energy of ATP hydrolysis to heavy metal ion translocation across membranes. A defining feature of P_1B-1-type ATPases is the presence of soluble metal binding domains at the N-terminus (N-MBDs). The N-MBDs exhibit a conserved ferredoxin-like fold, similar to that of soluble copper chaperones, and bind metal ions via a conserved CXXC motif. The N-MBDs enable Cu⁺ regulation of turnover rates apparently through Cu-sensitive interactions with catalytic domains. A. fulgidus CopA is unusual in that it contains both an N-terminal MBD and a C-terminal MBD (C-MBD). The functional role of the unique C-MBD has not been established. Here, we report the crystal structure of the apo, oxidized C-MBD to 2.0 !Å resolution. In the structure, two C-MBD monomers form a domain-swapped dimer, which has not been observed previously for similar domains. In addition, the interaction of the C-MBD with the other cytoplasmic domains of CopA, the ATP binding domain (ATPBD) and actuator domain (A-domain), has been investigated. Interestingly, the C-MBD interacts specifically with both of these domains, independent of the presence of Cu ⁺ or nucleotides. These data reinforce the uniqueness of the C-MBD and suggest a distinct structural role for the C-MBD in CopA transport.