Molecular insights into the activation of the ParA/MinD ATPase PomZ by the phase- separating PomY protein of the PomXYZ cell division regulatory system
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Abstract
Bacterial cell division requires precise spatial regulation that often involves a member of the family
of ParA/MinD-like ATPases. In Myxococcus xanthus, PomX, PomY, and PomZ form precisely
one MDa-sized, non-stoichiometric, nucleoid-associated assembly that associates with and
translocates across the nucleoid in a PomZ ATPase-dependent manner to position the cytokinetic
FtsZ-ring at midcell. Unlike other systems incorporating a ParA/MinD ATPase, the PomXYZ
system incorporates two ATPase-activating proteins (AAPs), PomX and PomY that stimulate
PomZ activity. While PomX AAP activity, similarly to other characterized AAPs of ParA/MinD
ATPases, resides in a short positively charged N-terminal peptide (PomXNPEP), the mechanism
underlying the activation of PomZ by the phase-separating PomY protein remained unknown. We
map PomY AAP activity to its C-terminal residues 496-682 (PomYR2gD) and show that this activity
is important for division site positioning and the initiation of cell division. Moreover, we found that
PomY biomolecular condensate formation is not required for the stimulation of PomZ ATPase
activity per se, but could potentially modulate the reaction by locally concentrating PomZ in PomY
biomolecular condensates, likely in its dimeric DNA-bound state. ATPase assays demonstrated
that the minimal stimulatory parts of PomX and PomY synergistically stimulate PomZ ATPase
activity, likely by binding at different sites on the PomZ dimer bound to DNA, as suggested by
structural modelling. These findings reveal a non-canonical AAP mechanism of PomY, while
PomXNPEP likely functions analogously to MinE, indicating that PomX and PomY act in concert
through distinct but complementary mechanisms to stimulate PomZ ATPase activity, thereby
efficiently driving the positioning of the cytokinetic FtsZ-ring.
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