Abstract
Current evidence suggests the occurrence of two classes of vacuolar-type H +-translocating inorganic pyrophosphatases (V-PPases): K +-insensitive proteins, identified in eukaryotes, bacteria and archaea, and K +-stimulated V-PPases, identified to date only in eukaryotes. Here, we describe the functional characterization of a thermostable V-PPase from the anaerobic hyperthermophilic bacterium Thermotoga maritima by heterologous expression in Saccharomyces cerevisiae. The activity of this 71-kDa membrane-embedded polypeptide has a near obligate requirement for K +, like the plant V-PPase, and its thermostability depends on the binding of Mg 2+. Phylogenetic analysis of protein sequences consistently assigned the T. maritima V-PPase to the K +-sensitive class of V-PPases so far only known for eukaryotes. The finding of a K +-stimulated V-PPase also in a member of a primitive eubacterial lineage strongly supports an ancient evolutionary origin of this group of pyrophosphate-energized proton pumps.
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