Reversible Membrane Tethering by ZipA Determines FtsZ Polymerization in Two and Three Dimensions

Area of Science:

• Microbiology
• Biophysics
• Cell Biology

Background:

• Bacterial cell division is crucial for life, involving the formation of a septum at the cell's midpoint.
• The FtsZ protein forms a dynamic ring (proto-ring) at the division site, acting as a scaffold for other divisome proteins.
• ZipA and FtsA are key proteins that tether FtsZ to the cytoplasmic membrane in Escherichia coli, but their quantitative interactions are poorly understood.

Purpose of the Study:

• To quantitatively characterize the multivalent interactions between FtsZ and ZipA at membrane surfaces.
• To investigate how ZipA density and FtsZ concentration influence FtsZ assembly states.
• To understand the role of nucleotides (GDP vs. GTP/GMPCPP) in FtsZ-ZipA interactions and FtsZ polymerization kinetics.

Main Methods:

• Incorporation of ZipA into supported lipid bilayers at controlled densities.
• Measurement of FtsZ binding to ZipA using quartz crystal microbalance and spectroscopic ellipsometry.
• Analysis of FtsZ assembly morphology (2D vs. 3D polymerization) under varying ZipA densities and FtsZ concentrations.

Main Results:

• ZipA attachment to the membrane enables FtsZ-GMPCPP to undergo both 2D polymerization on the membrane and 3D polymerization into solution.
• ZipA is essential for enriching FtsZ at the membrane surface, while the FtsZ bulk concentration determines the polymerization morphology.
• The nucleotide bound to FtsZ (GDP vs. GTP/GMPCPP) significantly affects the kinetics of ZipA-FtsZ association and dissociation.

Conclusions:

• This study provides quantitative insights into the initial events of bacterial cell division by elucidating FtsZ-ZipA interactions in a minimal membrane system.
• The findings highlight the distinct roles of ZipA and FtsZ concentration in directing FtsZ polymerization, crucial for divisome assembly.
• Understanding these fundamental interactions contributes to a comprehensive model of the bacterial division machinery.