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Related Concept Videos

Introduction to Actin01:26

Introduction to Actin

4.6K
Actin is a highly conserved cytoskeletal protein found abundantly in eukaryotic cells. It constitutes 10% weight of the total cellular protein in muscle cells, while in non-muscle cells, it is lower and makes up around 1–5 percent of the total cell protein. Actin found in the unicellular amoebae and complex multicellular animals is around 80% similar, demonstrating their conservation over a billion years of evolution.  Actin coding genes are conserved within species and across...
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Actin Polymerization and Cell Motility01:13

Actin Polymerization and Cell Motility

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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....
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Actin Polymerization01:42

Actin Polymerization

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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...
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Cytoskeletal Accessory Proteins01:13

Cytoskeletal Accessory Proteins

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The cytoskeleton is an essential cell component that plays several structural and functional roles. However, the filaments that make up the cytoskeleton cannot function independently and depend on the accessory or ancillary proteins to effectively carry out their function. Accessory proteins associate with cytoskeletal filaments and their monomers, aiding filament formation and function. They also help in the cross-communication among cytoskeletal filaments. Cytoskeletal accessory proteins are...
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Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

2.9K
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...
2.9K
Cytoskeletal Proteins in Bacteria01:29

Cytoskeletal Proteins in Bacteria

3.5K
Bacterial cells were initially considered simple, randomly organized structures lacking a cytoskeleton. However, the discovery of cytoskeleton homologs in bacteria led to the change of this opinion. Bacterial cytoskeletal filaments regulate the cell shape, cell polarity, cell division, and partitioning of plasmids during cell division. It was later discovered that bacterial cytoskeletal proteins, mainly actin and tubulin homologs, are diverse compared to their eukaryotic counterparts. On the...
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Related Experiment Video

Updated: May 3, 2026

Reconstitution of Actin-Based Motility with Commercially Available Proteins
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Reconstitution of Actin-Based Motility with Commercially Available Proteins

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Is P-protein actin-like?-not yet.

B A Palevitz1, P K Hepler

  • 1Department of Cellular and Comparative Biology, State University of New York, 11794, Stony Brook, New York, USA.

Planta
|January 18, 2014
PubMed
Summary

Heavy meromyosin (HMM) decorates microfilaments in Nitella, forming actin-like arrowheads. However, P-protein filaments in Phaseolus vulgaris do not bind HMM, refuting claims of their actin-like nature.

Area of Science:

  • Plant cell biology
  • Cytoskeletal dynamics
  • Protein characterization

Background:

  • Cytoplasmic streaming in plants relies on cytoskeletal elements.
  • The composition of P-protein in plant sieve elements remains debated.
  • Actin filaments are known to interact with heavy meromyosin (HMM).

Purpose of the Study:

  • To investigate the interaction of heavy meromyosin (HMM) with P-protein filaments.
  • To determine if P-protein exhibits actin-like properties.
  • To reconcile conflicting evidence regarding P-protein composition.

Main Methods:

  • In vitro and in situ decoration of cytoskeletal elements with rabbit heavy meromyosin (HMM).
  • Microscopic analysis of HMM binding patterns on microfilaments and P-protein filaments.

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Aip1p Dynamics Are Altered by the R256H Mutation in Actin

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Measuring Protein Binding to F-actin by Co-sedimentation

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  • Comparison of HMM-induced structures with known actin-heavy meromyosin (F-actin) interactions.

    • Main Results:

    • Microfilaments in Nitella flexilis internodes showed characteristic polarized arrowhead structures upon HMM binding, indicative of actin.
    • P-protein filaments in Phaseolus vulgaris sieve elements did not display similar arrowhead decorations when treated with HMM.
    • These findings contradict recent reports suggesting P-protein is actin-like.

    Conclusions:

    • P-protein filaments do not bind heavy meromyosin (HMM) and are therefore not actin-like.
    • The study supports a growing body of evidence against P-protein being composed of actin or tubulin.
    • This research clarifies the cytoskeletal composition of plant sieve elements.