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Actin Polymerization

Actin 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...

Generation of Straight or Branched Actin Filaments

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...

Mechanism of Filopodia Formation

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...

Malaria

Malaria

Malaria pathogenesis in humans reflects a delicate interplay between parasite biology and host response. Clinical illness reflects a host’s immune response to the parasite’s asexual replication cycle, which is often asymptomatic in individuals with partial immunity. From the parasite's perspective, transmission between mosquito and human with minimal host pathology is evolutionarily advantageous. Among the six Plasmodium species infecting humans, P. falciparum and P. vivax dominate in global...

Formation of Higher-order Actin Filaments

Formation 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...

Assembly of Cytoskeletal Filaments

Assembly 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...

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Related Experiment Video

Updated: Jun 9, 2026

Understanding the Development of Compensatory Pathways in a Mutant Malaria Parasite Harbouring Hypomorphic Allele of Plant-Like Kinases

Understanding the Development of Compensatory Pathways in a Mutant Malaria Parasite Harbouring Hypomorphic Allele of Plant-Like Kinases

Published on: November 22, 2024

Malaria parasite actin polymerization and filament structure.

Stephan Schmitz¹, Iwan A T Schaap, Jens Kleinjung

¹Division of Physical Biochemistry, National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom.

The Journal of Biological Chemistry

|September 10, 2010

Summary

Parasite actin filaments, though short in vivo, can be elongated and stabilized. Structural differences in Plasmodium falciparum actin compared to rabbit actin explain distinct filament dynamics crucial for parasite motility.

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Understanding the Development of Compensatory Pathways in a Mutant Malaria Parasite Harbouring Hypomorphic Allele of Plant-Like Kinases

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Published on: May 30, 2019

Area of Science:

Biochemistry
Cell Biology
Parasitology

Background:

Actin-myosin interactions regulate motility in apicomplexan parasites.
Parasite actin filaments (F-actin) are typically short and unstable in vivo and in vitro.
The structural basis for parasite F-actin dynamics remains largely unknown.

Purpose of the Study:

To investigate the structural basis and dynamics of Plasmodium falciparum actin filaments.
To compare the structure and stability of parasite actin with rabbit skeletal actin.
To understand how structural differences may influence parasite motility.

Main Methods:

Annealing of Plasmodium falciparum actin I (Pf-actin) with rabbit skeletal actin (RS-actin).
Fluorescence microscopy and gliding filament assays to assess hybrid filament stability and motility.
Negative stain electron microscopy and atomic force microscopy (AFM) to characterize filament structure.

Main Results:

Long, stable, hybrid actin filaments were formed by annealing Pf-actin and RS-actin.
Pure Pf-actin, stabilized by jasplakinolide (JAS), formed long filaments comparable to RS-actin.
AFM revealed distinct monomer stacking in Pf-actin, with a 10% larger helical pitch than RS-actin, suggesting a larger rotational angle between subunits.

Conclusions:

Structural differences in Pf-actin, potentially due to weaker inter- and intra-strand contacts, impact filament dynamics.
These structural variations are critical for regulating parasite motility.
The findings provide insights into the unique actin-based mechanisms in apicomplexan parasites.