Tuberculosis (TB), a disease caused by Mycobacterium tuberculosis (Mtb), claims 1.5 million lives annually. Upon inhalation, Mtb reaches the alveoli of the lungs, where it is engulfed by macrophages and enclosed in phagosomes, specialized vacuoles designed to degrade pathogens. Inside the phagosome, Mtb is exposed to various stresses, including nutrient deprivation, hypoxia, reactive oxygen and nitrogen species, and acidification. Despite these hostile conditions, Mtb is an exceptionally resilient pathogen, having evolved mechanisms to survive and persist within its host.
In a seminal study (PMID: 21925112), our lab discovered the accumulation of zinc within macrophage phagosomes during Mtb infection, leading to the identification of a novel zinc detoxification system in Mtb. This system consists of a membrane pump, CtpC, and a previously unknown metallochaperone, PacL1, which is essential for stabilizing CtpC (PMID: 35961955). Our research demonstrated that the PacL1/CtpC system is critical for Mtb replication within macrophages, suggesting that bacterial metal detoxification mechanisms represent promising targets for novel drug development.
Mtb possesses two additional homologous systems to PacL1/CtpC, named PacL2/CtpG and PacL3/CtpV. While CtpV has been implicated in copper tolerance, the role of CtpG remains unclear. Furthermore, the biological functions of PacL2 and PacL3 in Mtb were completely unknown. The first objective of my project was to investigate the involvement of the PacL2/CtpG and PacL3/CtpV systems in metal detoxification and pathogen survival during infection, as well as to elucidate the specific roles of the uncharacterized PacL2 and PacL3 proteins.
Preliminary findings from our laboratory revealed that PacL1, PacL2, and PacL3 colocalize in dynamic patches at the plasma membrane, suggesting the existence of uncharted metal efflux platforms composed of multiple metal chaperones (PacL proteins) and efflux pumps (Ctp proteins). However, the structure, composition, and dynamics of these platforms, along with the potential impact of their formation on efflux efficiency, remained completely unknown. Therefore, the second objective of my project was to characterize the composition and dynamics of these uncharted structures and to explore the collaborative functions of the PacL1/CtpC, PacL2/CtpG, and PacL3/CtpV systems.
