CtpB is a plasma membrane copper (I) transporting P-type ATPase of Mycobacterium tuberculosis

The intracellular concentration of heavy-metal cations, such as copper, nickel, and zinc is pivotal for the mycobacterial response to the hostile environment inside macrophages. To date, copper transport mediated by P-type ATPases across the mycobacterial plasma membrane has not been sufficiently explored.

In this work, the ATPase activity of the putative Mycobacterium tuberculosis P_1B-type ATPase CtpB was associated with copper (I) transport from mycobacterial cells. Although CtpB heterologously expressed in M. smegmatis induced tolerance to toxic concentrations of Cu²⁺ and a metal preference for Cu⁺, the disruption of ctpB in M. tuberculosis cells did not promote impaired cell growth or heavy-metal accumulation in whole mutant cells in cultures under high doses of copper. In addition, the Cu⁺ ATPase activity of CtpB embedded in the plasma membrane showed features of high affinity/slow turnover ATPases, with enzymatic parameters K_M 0.19 ± 0.04 µM and V_max 2.29 ± 0.10 nmol/mg min. In contrast, the ctpB gene transcription was activated in cells under culture conditions that mimicked the hostile intraphagosomal environment, such as hypoxia, nitrosative and oxidative stress, but not under high doses of copper.

The overall results suggest that M. tuberculosis CtpB is associated with Cu⁺ transport from mycobacterial cells possibly playing a role different from copper detoxification.