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Structural polymorphism of the ParM filament and dynamic instability
Vitold E Galkin1, Albina Orlova, Chris Rivera
1Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908-0733, USA. galkin@virginia.edu
Structure (London, England : 1993)
|September 15, 2009
Summary
Bacterial plasmid segregation protein ParM (an actin homolog) uses ATP or GTP for polymerization and depolymerization. Structural analysis reveals two subunit states, crucial for understanding ParM
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- The R1 plasmid in bacteria utilizes the ParM protein for segregation.
- ParM is an actin homolog that functions through polymerization and depolymerization cycles.
Purpose of the Study:
- To investigate the polymerization kinetics and structural properties of ParM.
- To elucidate the role of nucleotide binding (ATP/GTP) in ParM filament dynamics.
- To determine the structural basis for ParM's dynamic instability.
Main Methods:
- Kinetic assays to measure polymerization and stability with ATP and GTP.
- Electron cryo-microscopy (cryo-EM) to analyze ParM filament structure.
- Structural comparison with F-actin.
Main Results:
- ParM exhibits similar polymerization kinetics and stability with ATP and GTP, but prefers ATP.
- Cryo-EM revealed heterogeneity in ParM filaments, including variable twist and axial rise.
- ParM subunits exist in two states (open/closed nucleotide-binding cleft), influenced by the bound nucleotide.
- The protomer interface differs between states and from F-actin.
Conclusions:
- The closed nucleotide-binding cleft is necessary, but not sufficient, for ParM polymerization.
- Structural differences from F-actin highlight ParM's unique mechanism.
- These findings provide a structural framework for understanding ParM filament dynamics and plasmid segregation.
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