P-type ATPases are involved in heavy metal transport across the plasma membrane. Some Mycobacterium tuberculosis P-type ATPases are induced during infection, suggesting that this type of transporter could play a critical role in mycobacterial survival. To date, the ion specificity of M. tuberculosis heavy metal-transporting P-ATPases is not well understood. In this work, we observed that, although divalent heavy metal cations such as Cu, Co, Ni, Zn Cd and Pb stimulate the ATPase activity of the putative P-type ATPase CtpG in the plasma membrane, whole cells of M. smegmatis expressing CtpG only tolerate high levels of Cd and Cu. As indicator of the catalytic constant, Michaelis-Menten kinetics showed that CtpG embedded in the mycobacterial cell membrane has a V /K ratio 7.4-fold higher for Cd than for Cu ions. Thus, although CtpG can accept different substrates in vitro, this P-type ATPase transports Cd more efficiently than other heavy metal cations across the mycobacterial plasma membrane.
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