Identification of a pH regulated Na+/H+ antiporter of Methanococcus jannaschii

AbstractThe genome of the hyperthermophilic archaeon Methanococcus jannaschii contains three Na+/H+ antiporter related genes Mj0057, Mj1521 and Mj1275. Comparative sequence alignments revealed that Mj0057 and Mj1521 belong to the NhaP family whereas Mj1275 is a member of the NapA family. The genes were cloned and expressed in the double mutant Escherichia coli strain Frag144 (ΔnhaA, ΔnhaB) to analyze their capability of mediating ΔpH driven Na+ flux in everted vesicles. From the tested clones only Mj0057 displayed Na+ (Li+)/H+ antiporter activity. The transport was pH dependent and occurred at pH 7.0 and below. At pH 6.0 the apparent Km values for Na+ and Li+ were approximately 10 and 2.5 mM, respectively