Role of the N-Terminal Tail of Metal-Transporting P(1B)-type ATPases from Genome-Wide Analysis and Molecular Dynamics Simulations

Copper is an essential trace metal but can be potentially toxic in vivo. Consequently, its intracellular concentration and distribution is tightly controlled. A widespread system involved in maintaining copper homeostasis in a variety of prokaryotic and eukaryotic organisms involves a P-type ATPase, which pumps the metal ion from the cytosol at the expense of ATP hydrolysis. Copper-transporting ATPases of this kind are often associated with a small soluble metal-transporter (metallochaperone). In this work, we investigated the occurrence and properties of the ATPases and, partly, of their partner metallochaperones. We found that the latter proteins are typically encoded in organisms containing also ATPases of the subtypes 1B-1 or 1B-2. These subtypes have a characteristically extended N-terminal cytoplasmic tail that contains multiple metal-binding domains (MBDs), which can receive the metal ion from the metallochaperone. We observed a significant variability in the number and spacing in sequence of the MBDs. On the basis of molecular dynamics simulations, we proposed that the MBDs could be quite free to reorient with respect to one another. The relative conformational freedom increased rapidly with the length of the linker between the MBDs. Also based on available experimental studies, these data suggested that the reciprocal mobility of the MBDs is instrumental to permit the tuning of the selectivity and/or affinity of the ATPase for the substrate as well as to modulate the enzymatic activity of the system. We additionally detected a small but significant number of instances in which a metallochaperone is likely to interact directly with the transmembrane domain of P-type ATPases lacking cytoplasmic MBDs.