Interdomain interactions modulate collective dynamics of the metal-binding domains in the Wilson disease protein

Wilson disease protein or ATP7B is a key player in human copper (Cu) homeostasis. Belonging to the P(1B) type subfamily of ATPases, its N-terminal region contains six soluble domains (WD1-WD6) connected by linkers that vary in length. These domains share a similar fold and bind Cu(I) in the conserved motif MCXXC. It is unclear why there are six similar domains in the human protein (whereas bacteria and yeast contain only one or two) and why the human metallochaperone Atox1 delivers Cu(I) to only a subset of them. It has been speculated that the extra domains in humans regulate the ATPase in response to different Cu levels, suggesting that, although usually separated by long linkers, the domains can communicate with each other. Here, we performed extensive molecular dynamics simulations on three two-domain constructs in the apo- (WD12, WD34, WD56) and holo- (Cu(I) added to the most C-terminal domain of each construct: WD12c, WD34c and WD56c) forms to investigate how covalent linkage between domains and Cu(I) binding regulate their conformational dynamics. Our results suggest that when linked together the domains do not act as individual units but instead exhibit a distinct pattern of correlated motions, which are domain dependent and modulated by the presence of Cu. Conformational plasticity and degree of reorientation did not correlate with linker length, suggesting strong interdomain communication regardless of the linker length. Our computational findings suggest that cooperativity and long-range communication between domains may be important for the function and regulation of the ATPase.