The structure of the hexameric fungal proton pump Pma1 reveals its mechanism of autoinhibition and interactions with lipids.

The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a P-type ATPase that transports Ca2+ from the cytosol into the sarco(endo)plasmic reticulum (SR/ER) lumen, driven by ATP. This primary transport activity depends on tight coupling between movements of the transmembrane helices forming the two Ca2+-binding sites and the cytosolic headpiece mediating ATP hydrolysis. We have addressed the molecular basis for this intramolecular communication by analyzing the structure and functional properties of the SERCA mutant E340A. The mutated Glu340 residue is strictly conserved among the P-type ATPase family of membrane transporters and is located at a seemingly strategic position at the interface between the phosphorylation domain and the cytosolic ends of 5 of SERCA’s 10 transmembrane helices. The mutant displays a marked slowing of the Ca2+-binding kinetics, and its crystal structure in the presence of Ca2+ and ATP analog reveals a rotated headpiece, altered connectivity between the cytosolic domains, and an altered hydrogen bonding pattern around residue 340. Supported by molecular dynamics simulations, we conclude that the E340A mutation causes a stabilization of the Ca2+ sites in a more occluded state, hence displaying slowed dynamics. This finding underpins a crucial role of Glu340 in interdomain communication between the headpiece and the Ca2+-binding transmembrane region.

The sarco(endo)plasmic reticulum Ca 2+ -ATPase (SERCA) transports Ca 2+ ions from the cytosol into the SR/ER lumen. SERCA's activity is dependent on a tight coupling between movements of the transmembrane helices that comprise the two Ca 2+ binding sites and the cytosolic ATPase headpiece. We have addressed the molecular basis for this intramolecular communication by analysing the structure and functional properties of the SERCA mutant E340A. The conserved residue Glu340 is located at a strategic position in the ATPase, at the interface between the phosphorylation domain and the cytosolic ends of six out of SERCA's ten transmembrane helices. The mutant displays a reduced rate of binding Ca 2+ ions from the cytosol. The structure of E340A reveals a rotated headpiece, altered connectivity between the cytosolic domains and an altered interaction pattern around the mutated residue Glu340. Supported by molecular dynamics simulations, we conclude that the E340A mutation causes a stabilisation of SERCA in a more occluded state, causing slowed dynamics in the ion binding region. This finding underpins the crucial role of Glu340 in the interdomain communication of SERCA.