Characterization of a Listeria monocytogenes Ca(2+) pump: a SERCA-type ATPase with only one Ca(2+)-binding site

We have characterized a putative Ca(2+)-ATPase from the pathogenic bacterium Listeria monocytogenes with the locus tag lmo0841. The purified and detergent-solubilized protein, which we have named Listeria monocytogenes Ca(2+)-ATPase 1 (LMCA1), performs a Ca(2+)-dependent ATP hydrolysis and actively transports Ca(2+) after reconstitution in dioleoylphosphatidyl-choline vesicles. Despite a high sequence similarity to the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA1a) and plasma membrane Ca(2+)-ATPase (PMCA), LMCA1 exhibits important biochemical differences such as a low Ca(2+) affinity (K(0.5) ～80 μm) and a high pH optimum (pH ～9). Mutational studies indicate that the unusually high pH optimum can be partially ascribed to the presence of an arginine residue (Arg-795), corresponding in sequence alignments to the Glu-908 position at Ca(2+) binding site I of rabbit SERCA1a, but probably with an exposed position in LMCA1. The arginine is characteristic of a large group of putative bacterial Ca(2+)-ATPases. Moreover, we demonstrate that H(+) is countertransported with a transport stoichiometry of 1 Ca(2+) out and 1 H(+) in per ATP hydrolyzed. The ATPase may serve an important function by removing Ca(2+) from the microorganism in environmental conditions when e.g. stressed by high Ca(2+) and alkaline pH.