A thermostable K+‐stimulated vacuolar‐type pyrophosphatase from the hyperthermophilic bacterium Thermotoga maritima

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 Mg²⁺. 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.