The crystal structure of the Ca2+-ATPase 1 from Listeria monocytogenes reveals a pump primed for dephosphorylation

Bacteria regulate intracellular calcium concentrations by exporting calcium from the cell using active transporters. These transporters include homologues of the mammalian sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), which has served as a paradigm for the structure and mechanism of P-type ATPase ion transport. Here we present three crystal structures of the Ca2+-ATPase 1 from Listeria monocytogenes (LMCA1). Structures with BeF3− mimicking a phosphoenzyme state reveal an intermediate between the outward-open E2P and the proton-occluded E2-P* conformations known for SERCA. This suggests that LMCA1 pre-organizes for dephosphorylation already at the E2P state, consistent with the rapid dephosphorylation of this pump and observations from single-molecule studies. Comparison of ion binding sites show that an arginine side-chain occupies the position equivalent to the calcium binding site I in SERCA leaving a single Ca2+-binding site in LMCA1, corresponding to SERCA site II. Absence of putative proton pathways suggest a direct mechanism of proton counter transport through the Ca2+ exchange pathways. In total, the new structures provide insight into the evolutionary divergence and conserved features of an important class of ion transporters.