Pma1 is an alkali/alkaline earth metal cation ATPase that preferentially transports Na+ and K+ across the Mycobacterium smegmatis plasma membrane

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Mycobacterium smegmatis Pma1 is the orthologue of M. tuberculosis P-type ATPase cation transporter CtpF, which is activated under stress conditions, such as hypoxia, starvation and response to antituberculous and toxic substances. The function of Pma1 in the mycobacterial processes across the plasma membrane has not been characterised. In this work, bioinformatic analyses revealed that Pma1 likely contains potential sites for, Na+, K+ and Ca2+ binding and transport. Accordingly, RT-qPCR experiments showed that M. smegmatis pma1 transcription is stimulated by sub-lethal doses of Na+, K+ and Ca2+; in addition, the ATPase activity of plasma membrane vesicles in recombinant Pma1-expressing M. smegmatis cells is stimulated by treatment with these cations. In contrast, M. smegmatis cells homologously expressing Pma1 displayed tolerance to high doses of Na+ and K+ but not to Ca2+ ions. Consistently, the recombinant protein Km embedded in plasma membrane demonstrated that Ca2+ has more affinity for Pma1 than Na+ and K+ ions; furthermore, the estimation of Vmax/Km suggests that Na+ and K+ ions are more efficiently translocated than Ca2+. Thus, these results strongly suggest that Pma1 is a promiscuous alkali/alkaline earth cation ATPase that preferentially transports Na+ and/or K+ across the mycobacterial plasma membrane.