title: Die PomXYZ Zellteilungsregulatoren organisieren sich auf dem bakteriellen Chromosom um Zellteilungen auf die Zellmitte zu beschränken im Stäbchen-förmigen Bakterium Myxococcus xanthus
title: The PomXYZ cell division regulators self-organize on the nucleoid to position cell division at midcell in the rod-shaped bacterium Myxococcus xanthus
Creators: name: Schumacher, Dominik
Publisher: name: Philipps-Universität Marburg
Year: 2016
Subjects: Zellteilungspositionierung
FtsZ
ParA
Zellteilung
cell division positioning
Prokaryoten
Life sciences
Biowissenschaften, Biologie
Bacterial nucleoid

description: Accurate positioning of the
      division site is essential to produce daughter cells with the
      correct size, and chromosome content. Generally, the first
      known event of bacterial cell division is the accumulation of
      FtsZ at the incipient cell division site to form the
      circumferential, ring-like structure Z-ring. In bacteria,
      positioning of the division site occurs at the level of
      formation of the FtsZ-ring. While the cytokinesis machinery
      is conserved throughout bacteria, the mechanisms to position
      the Z-ring are diverse. The rod-shaped social bacterium
      Myxococcus xanthus divides precisely by binary fission at
      midcell but it lacks all the known systems that regulate
      Z-ring formation in other bacteria. Instead two novel
      regulators PomX and PomY together with the ParA ATPase PomZ
      stimulate formation and positioning of the Z-ring at midcell.
      PomXYZ interact and form a complex that associates with the
      nucleoid to translocate towards the mid-nucleoid, which
      coincides with midcell before nucleoids have segregated, by
      biased random motion. At the mid-nucleoid, at midcell, the
      PomXYZ complex undergoes constrained motion, not leaving
      midcell. Our experimental data show that cluster localization
      at midcell is independent of FtsZ and that clusters localize
      at midcell before Z-rings form. By contrast cluster
      localization at midcell depends on the ATPase PomZ, its
      associated ability to hydrolyze ATP and its ability to bind
      non-specifically to DNA. ATP-hydrolysis by PomZ is stimulated
      by PomX as well as by PomY in the presence of DNA,
      demonstrating that PomZ is the first ParA ATPase in which
      ATP-hydrolysis is stimulated by two ATPase activating
      proteins (AAP’s). We show that interference with
      ATP-hydrolysis, by mutational analysis, affects cluster
      translocation towards midcell. PomZ on its own interacts with
      the nucleoid and recruits a complex of PomX and PomY to the
      nucleoid. By FRAP experiments we show that PomZ is highly
      dynamic in the PomXYZ complex, where ATP-hydrolysis takes
      place and on the nucleoid. Our experimental data support a
      flux-based mechanism for the positioning of the PomXYZ
      complex by the ParA ATPase PomZ. In this model, the diffusive
      random PomZ dynamics on the nucleoid result in diffusive
      fluxes of PomZ on the nucleoid from either side into the
      PomXYZ cluster. These fluxes scale with the cellular
      asymmetry of the cluster within the cell and convert this
      cellular asymmetry into a PomZ concentration gradient over
      the PomXYZ complex. This gradient together with the
      PomZ-associated ATP-hydrolysis translocates the complex
      towards the higher concentration of PomZ to midcell. At
      midcell, which coincides with middle of the nucleoid, the
      diffusive PomZ fluxes equalize, resulting in constrained
      motion. To understand the molecular details of
      ATP-hydrolysis, a previously identified pomXK13A,R15A mutant
      was analyzed for its defect in PomXYZ-dependent positioning
      of the cell division site. Our in vivo and in vitro data show
      that the PomXK13A;R15A variant has a defect in stimulating
      PomZ ATP-hydrolysis, strongly suggesting that the N-terminal
      part of PomX interacts with PomZ to stimulate ATP-hydrolysis,
      similar to other ATPase activating proteins. In summary we
      identified two novel cell division regulators that work in
      concert with PomZ to position and promote cell division at
      midcell. Our data provides insights into the function of
      ParA-ATPases, which in this case is PomZ, and reveal that the
      PomXYZ system is a novel system that positions cell division
      at midcell most likely by recruiting the Z-ring to the
      incipient cell division site.
description: Accurate positioning of the
      division site is essential to produce daughter cells with the
      correct size, and chromosome content. Generally, the first
      known event of bacterial cell division is the accumulation of
      FtsZ at the incipient cell division site to form the
      circumferential, ring-like structure Z-ring. In bacteria,
      positioning of the division site occurs at the level of
      formation of the FtsZ-ring. While the cytokinesis machinery
      is conserved throughout bacteria, the mechanisms to position
      the Z-ring are diverse. The rod-shaped social bacterium
      Myxococcus xanthus divides precisely by binary fission at
      midcell but it lacks all the known systems that regulate
      Z-ring formation in other bacteria. Instead two novel
      regulators PomX and PomY together with the ParA ATPase PomZ
      stimulate formation and positioning of the Z-ring at midcell.
      PomXYZ interact and form a complex that associates with the
      nucleoid to translocate towards the mid-nucleoid, which
      coincides with midcell before nucleoids have segregated, by
      biased random motion. At the mid-nucleoid, at midcell, the
      PomXYZ complex undergoes constrained motion, not leaving
      midcell. Our experimental data show that cluster localization
      at midcell is independent of FtsZ and that clusters localize
      at midcell before Z-rings form. By contrast cluster
      localization at midcell depends on the ATPase PomZ, its
      associated ability to hydrolyze ATP and its ability to bind
      non-specifically to DNA. ATP-hydrolysis by PomZ is stimulated
      by PomX as well as by PomY in the presence of DNA,
      demonstrating that PomZ is the first ParA ATPase in which
      ATP-hydrolysis is stimulated by two ATPase activating
      proteins (AAP’s). We show that interference with
      ATP-hydrolysis, by mutational analysis, affects cluster
      translocation towards midcell. PomZ on its own interacts with
      the nucleoid and recruits a complex of PomX and PomY to the
      nucleoid. By FRAP experiments we show that PomZ is highly
      dynamic in the PomXYZ complex, where ATP-hydrolysis takes
      place and on the nucleoid. Our experimental data support a
      flux-based mechanism for the positioning of the PomXYZ
      complex by the ParA ATPase PomZ. In this model, the diffusive
      random PomZ dynamics on the nucleoid result in diffusive
      fluxes of PomZ on the nucleoid from either side into the
      PomXYZ cluster. These fluxes scale with the cellular
      asymmetry of the cluster within the cell and convert this
      cellular asymmetry into a PomZ concentration gradient over
      the PomXYZ complex. This gradient together with the
      PomZ-associated ATP-hydrolysis translocates the complex
      towards the higher concentration of PomZ to midcell. At
      midcell, which coincides with middle of the nucleoid, the
      diffusive PomZ fluxes equalize, resulting in constrained
      motion. To understand the molecular details of
      ATP-hydrolysis, a previously identified pomXK13A,R15A mutant
      was analyzed for its defect in PomXYZ-dependent positioning
      of the cell division site. Our in vivo and in vitro data show
      that the PomXK13A;R15A variant has a defect in stimulating
      PomZ ATP-hydrolysis, strongly suggesting that the N-terminal
      part of PomX interacts with PomZ to stimulate ATP-hydrolysis,
      similar to other ATPase activating proteins. In summary we
      identified two novel cell division regulators that work in
      concert with PomZ to position and promote cell division at
      midcell. Our data provides insights into the function of
      ParA-ATPases, which in this case is PomZ, and reveal that the
      PomXYZ system is a novel system that positions cell division
      at midcell most likely by recruiting the Z-ring to the
      incipient cell division site.