PE17 localizes in close proximity to mitochondrial membranes and
results in extensive changes to mitochondrial morphology and mass
To test the hypothesis that mitochondrial fragmentation is induced by
other secreted Mtb proteins which require release to the host cytoplasm
via ESAT-6 activity, we scanned the literature for reports citing
localization or effects of secreted Mtb proteins on mitochondria. In a
screen of Mtb secreted proteins, Stamm et al. reported that PE17
localizes to the mitochondria in HeLa cells (Stamm et al. , 2019).
To confirm this observation, we transiently transfected A549 AECs with a
constitutively-expressing myc-tagged PE17 construct and performed
immunofluoresence microscopy using anti-myc and anti-COXIV antibodies to
determine whether PE17 localized to mitochondria. Interestingly, in our
hands, PE17 did not completely co-localize with mitochondria and was
located perinuclearly, adjacent to the few remaining mitochondrial
structures (Figure 1C). In addition, the PE17-positive structures
correlated with large occlusions in the cytoplasm in transmitted light
images (Figure 1C, arrows) and appeared as clusters of circular
structures (Figure 1D). As there appeared to be a visible decrease in
mitochondrial mass in PE17-expressing cells, we analyzed the percent
area of mitochondria within transfected cells that did and did not
express PE17. As predicted, expression of PE17 significantly decreased
mitochondrial mass (Figure 1E, p-value <0.0001).