Membrane Mimetics Control Internal Hydration and Catalytic Activity of the Copper ATPase LpCopA from Legionella...

Membrane protein function is strongly influenced by the surrounding lipid bilayer through specific lipid-protein interactions and collective membrane properties. Here, we investigated how the membrane environment modulates internal hydration and catalytic activity of the P_1B-type copper ATPase LpCopA. LpCopA variants labeled with 6-bromoacetyl-2-dimethylaminonaphthalene (BADAN) were reconstituted in Escherichia coli lipid-doped mixed micelles, membrane scaffold protein nanodiscs, and diisobutylene-maleic acid lipid particles (DIBMALPs). Local hydration near the conserved metal-binding cysteines C382 and C384 was assessed by fluorescence spectroscopy in the presence of polyethylene glycol 1500 (PEG-1500), and ATPase activity was determined in the corresponding membrane mimetics. C382 exhibited a more hydrated local environment than C384. In mixed micelles, the osmolyte-induced spectral response corresponded to an apparent hydration volume change of approximately 800 ų, equivalent to about 25 water molecules; the corresponding change in nanodiscs was less than half as large. ATPase activity increased with osmotically responsive internal hydration, whereas DIBMALPs showed minimal hydration changes and strongly reduced ATPase activity. These findings suggest that membrane-dependent transmembrane packing modulates internal hydration and LpCopA activity. Energetic estimates further support a model in which hydration-dependent transmembrane expansion against membrane lateral pressure contributes to the free-energy barrier associated with conformational transitions during the catalytic cycle.