Related Experiment Video

Updated: Jun 20, 2026

DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers
08:00

DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers

Published on: October 25, 2017

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
PubMed

Insights

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.

More Related Videos

Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles08:02

Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles

Published on: May 5, 2022

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives09:22

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

Published on: February 7, 2017

Related Concept Videos

Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

The straight or branched structure formation of actin filaments is controlled by nucleating proteins such as the formins and Arp2/3 complex. Formin-mediated assembly results in straight filaments, whereas Arp2/3 protein complex-mediated assembly results in branched actin filaments.
Arp2/3 Complex
Arp2/3 complex is a seven-subunit complex consisting of two proteins similar to actin- Arp2 and Arp3, and five other subunits that help keep Arp2 and Arp3 inactive. When required, the complex is...
Disassembly of Intermediate Filaments01:35

Disassembly of Intermediate Filaments

Intermediate filaments (IFs) do not undergo spontaneous disassembly. Enzymes, kinases, and phosphatases add and remove phosphates from specific sites to regulate their disassembly. The IF concentration in the cytoplasm also regulates the disassembly. If the concentration crosses a threshold, it activates the protein kinases in the vicinity, allowing the phosphorylation of IFs.
Keratin proteins, found at the cell periphery near cell junctions, undergo a cycle of assembly and disassembly. In Type...
Formation of Intermediate Filaments00:57

Formation of Intermediate Filaments

Intermediate filaments are cytoskeletal proteins with higher tensile strength and flexibility than microfilaments and microtubules. Unlike the other two cytoskeletal proteins, intermediate filament formation lacks the enzymatic activity to hydrolyze nucleotides like ATP and GTP to generate energy for polymerization. Therefore, the formation of intermediate filaments is multistep self-assembly. The involvement of any accessory proteins in intermediate filament formation has not yet been reported.
Adaptability of Cytoskeletal Filaments01:12

Adaptability of Cytoskeletal Filaments

The cytoskeleton is a complex dynamic structure performing varied functions based on cellular requirements. The adaptability of the individual filaments in the cytoskeleton determines their ability to perform various functions within the cell. It can undergo rapid reorganization during processes like cell division or remain stable for several hours as in the interphase. The adaptability of these filaments depends on stringent regulatory mechanisms. The microfilament and microtubules of the...
Mechanism of Filopodia Formation01:39

Mechanism of Filopodia Formation

Filopodia are thin, actin-rich cellular protrusions that play an important role in many fundamental cellular functions. They vary in their occurrence, length, and positioning in different cell types, suggesting their diverse roles.
Their main function is to guide migrating cells during normal tissue morphogenesis or cancer metastasis by recognizing and making initial contacts with the extracellular matrix. However, they can also act as stationary cell anchors or help to establish communication...
Microtubule Instability02:17

Microtubule Instability

Microtubules are hollow cylindrical filaments having a diameter of approximately 25 nm and a length that varies from 200 nm to 25 μm. GTP-bound tubulin subunits form αβ-heterodimers for microtubule assembly. These core building blocks interact longitudinally, polymerizing into protofilaments. The protofilaments then interact with one another through lateral bonding forces to form stable cylindrical microtubules. These cylindrical filaments are dynamic as they undergo repeated assembly and...