The ligand dependent interactions between cytoplasmic domains in Cu+ transporter, Archaeoglobus fulgidus

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The ligand dependent interactions between cytoplasmic domains in Cu+ transporter, Archaeoglobus fulgidus

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Cu+-ATPases receive Cu+ from specific chaperones via ligand exchange and subsequently drive the metal efflux from the cell cytoplasms. Cu+-ATPases have two transmembrane metal binding/transport sites (TM-MBS) and various cytoplasmic domains: the actuator (A-domain) and ATP binding domains (ATPBD), and regulatory N-terminal metal binding domains (N-MBD). Archaeoglobus fulgidus CopA, the Cu+-ATPase used in these studies, contains a single N-MBD and an apparently non-functional C-terminal MBD. The Cu+ dependent interaction of N-MBD and ATPBD was postulated as a possible mechanism for enzyme regulation. The Cu+ transfer from the chaperone to CopA is independent of the N-MBD capability to bind Cu+. Therefore, we hypothesized that ligand (Cu+ or nucleotide) binding to cytoplasmic domains might affect the interactions between the cytoplasmic domains. To test these ideas, the interactions among isolated cytoplasmic domains were characterized. Studies using isolated domains showed that while the N-MBD interacts with ATPBD, the presence of Cu+ or nucleotide (ADP) prevents this interaction. The N-MBD does not interact with the A domain. Alternatively, the C-MBD interacts with both ATPBD and A-domains in a ligand independent fashion. Only one Cu+ is transferred to CopA in absence of nucleotides, while the presence of ADP allows full loading of TM-MBS. These results suggest that the ligand binding affects the interactions between the cytoplasmic domains, and also change the conformation of CopA to help it accept the second Cu+ from chaperone.

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