Role in metal homeostasis of CtpD, a Co 2+ transporting P1B4-ATPase of Mycobacterium smegmatis

Abstract

Genetic studies in the tuberculosis mouse model have suggested that mycobacterial metal efflux systems, such as the P1B4-ATPase CtpD, are important for pathogenesis. The specificity for substrate metals largely determines the function of these ATPases; however, various substrates have been reported for bacterial and plant P1B4-ATPases leaving their function uncertain. Here we describe the functional role of the CtpD protein of Mycobacterium smegmatis. An M. smegmatis mutant strain lacking the ctpD gene was hypersensitive to Co 2+ and Ni 2+ and accumulated these metals in the cytoplasm. ctpD transcription was induced by both Co 2+ and superoxide stress. Biochemical characterization of heterologously expressed, affinity-purified CtpD showed that thisATPase is activated by Co 2+, Ni 2+ and to a lesser extend Zn 2+ (20% of maximum activity). The protein was also able to bind one Co 2+, Ni 2+ or Zn 2+ to its transmembrane transport site. These observations indicate that CtpD is important for Co 2+ and Ni 2+ homeostasis in M. smegmatis, and that M. tuberculosis CtpD orthologue could be involved in metal detoxification and resisting cellular oxidative stress by modulating the intracellular concentration of these metals. © 2012 Blackwell Publishing Ltd.