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Updated: Aug 7, 2026
08:02
Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles
Published on: May 5, 2022
Actin filament assembly driven by distributive polymerases clustered on membrane surfaces
R Dyche Mullins1, Jane Kondev2, Kristen Skruber1
1Department of Cellular and Molecular Pharmacology University of California San Francisco San Francisco, California.
Biophysical Journal
|August 6, 2026
Summary
Membrane surfaces accelerate actin filament assembly by clustering proteins, enhancing polymerization speed. This surface-mediated process can outpace solution-based elongation, even under force.
Area of Science:
- Cell Biology
- Biophysics
- Biochemistry
Background:
- Actin filaments form branched networks via the Arp2/3 complex, driving cellular processes like membrane protrusion.
- WAVE-family proteins are key nucleation-promoting factors involved in actin assembly at cellular membranes.
Purpose of the Study:
- To theoretically and computationally investigate how membrane surfaces accelerate actin filament assembly.
- To determine the impact of protein clustering and actin concentration on filament elongation rates.
Main Methods:
- Utilized theoretical modeling and computer simulations.
- Incorporated protein clustering, actin monomer binding, and profilin-actin complex dynamics.
- Analyzed the role of thermal fluctuations and random walks of filament tips on membrane surfaces.
Main Results:
- Membrane surfaces accelerate actin filament assembly through protein clustering, enhancing polymerization.
- Surface-mediated polymerization can exceed solution-mediated elongation, particularly at high actin concentrations (>100 μM).
- Profilin dissociation time reduces the advantage of surface polymerases without force, but force enhances their effect.
Conclusions:
- Surface-mediated actin polymerization is a significant factor in cellular processes involving membrane dynamics.
- The interplay between actin concentration, protein clustering, and mechanical forces dictates filament assembly efficiency.
- Understanding these mechanisms is crucial for comprehending cell motility and morphogenesis.
Related Concept Videos
01:42Actin Polymerization
Actin polymerization occurs through the head-to-tail association of binding sites on monomeric actin or G-actin to form filamentous or F-actin. The polymerization can be divided into three phases ̶ nucleation, elongation, and steady-state phase.
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...
01:39Mechanism 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...
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...
01:13Actin Polymerization and Cell Motility
Actin is a family of globular proteins that are highly abundant in eukaryotic cells. It makes up approximately 1-5% of total cell protein concentration. Actin monomers polymerize to form a complex network of polarized filaments, the actin cytoskeleton, that plays a crucial role in many cellular processes, including cell motility, division, endocytosis, and metastasis of cancer cells.
Actin cytoskeleton dynamics can produce pushing, pulling, and resistance forces that help the cell to migrate.
Actin cytoskeleton dynamics can produce pushing, pulling, and resistance forces that help the cell to migrate.
01:11Formation of Higher-order Actin Filaments
The polymerization of G-actin monomers into filamentous F-actin is a multi-step process. Once the F-actins are formed, they can bundle together in different arrangements to form higher-order networks and regulate cellular functions. Common examples include the formation of lamellipodia and filopodia at the cell's leading edge by actin reorganization in a migrating cell. The microvilli on the brush border epithelial cells are also formed through the F-actin network.
The high-order actin networks...
The high-order actin networks...
01:18Assembly of Cytoskeletal Filaments
Cytoskeletal filaments are polymeric forms of smaller protein subunits. However, individual cytoskeletal filaments may easily disassemble or associate with other similar filaments to form rigid structures. Microfilaments, made of actin monomers, rely on actin-binding proteins to form bundles and create networks of individual actin filaments. Microtubules rely on microtubule-associated proteins (MAPs) to form sturdy cylindrical structures. However, the proteins involved in forming complex...
01:14Generation 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...
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...