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Related Concept Videos

Actin and Myosin in Muscle Contraction01:16

Actin and Myosin in Muscle Contraction

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Actin and myosin are contractile proteins that form the sarcomere found in skeletal muscle tissues for regulating muscle contraction. Actin, a globular contractile protein, interacts with myosin for muscle contraction. The skeletal tissue appears striped or striated under a microscope due to the repeated arrangement of contractile proteins actin and myosin along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes...
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Myosins are a family of molecular motor proteins, first identified in the skeletal muscles, where they are responsible for muscle contraction. Along with their role in muscle contraction, these proteins also play a role in the intracellular transport of molecules and vesicles. There are twenty-four classes of myosins based on their domain sequence and organization. Of the twenty-four, six classes (Myosin I, Myosin II, Myosin V, Myosin VI, Myosin VII, and Myosin X)  have been well...
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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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The Sarcomere01:08

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A sarcomere is a microscopic segment repeating in a myofibril. The sarcomere fundamentally consists of two main myofilaments: thick filaments called myosin and thin filaments called actin. These filaments interact by sliding past each other in response to stimulus. In addition to myosin and actin, several other proteins, such as tropomyosin, troponin, titin, nebulin, myomesin, α-actinin, and dystrophin, play crucial roles in regulating, structuring, and functioning of the sarcomere.
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Actin Filament Depolymerization01:19

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Formation of Higher-order Actin Filaments01:11

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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.
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Updated: Dec 29, 2025

Tuning the Contractility and Deformation Modes of Active Actin-Based Assemblies In Vitro: From Two-Dimensional Active Networks to Liquid Crystal Drops
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Functional, chymotryptically split actin and its interaction with myosin subfragment 1.

K Konno1

  • 1Cardiovascular Research Institute, University of California, San Francisco 94143.

Biochemistry
|June 16, 1987
PubMed
Summary
This summary is machine-generated.

Chymotryptically split actin, a 35-kDa-10-kDa complex, retains intact actin properties and binds strongly to myosin subfragment 1 (S-1). This split actin enables carbodiimide-induced cross-linking with S-1, leading to superactivation of S-1 ATPase activity.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Muscle Physiology

Background:

  • Actin is a crucial protein in muscle contraction and cellular motility.
  • Understanding actin's interaction with myosin is key to elucidating muscle function.
  • Limited proteolysis offers a method to study specific domains of actin.

Purpose of the Study:

  • To characterize chymotryptically cleaved actin fragments and their functional properties.
  • To investigate the binding and cross-linking interactions between split actin and myosin subfragment 1 (S-1).
  • To assess the impact of these interactions on myosin S-1 ATPase activity.

Main Methods:

  • Chymotryptic digestion of G-actin to produce 35-kDa-10-kDa (split actin) and 33-kDa-10-kDa complexes.
  • Polymerization assays using KCl and MgCl2.
  • Binding studies with myosin subfragment 1 (S-1) in the rigor state.
  • Carbodiimide-induced cross-linking to identify binding sites.
  • ATPase activity assays for S-1.

Main Results:

  • Split actin (35-kDa-10-kDa) polymerizes and binds strongly to S-1 in a 1:1 stoichiometry, similar to intact actin.
  • Carbodiimide cross-linking occurs between the N-terminal 10-kDa fragment of split actin and the 20-kDa domain of S-1.
  • Cross-linked split actin superactivates S-1 ATPase activity, while non-cross-linked split actin shows lesser activation.
  • No cross-linking was observed between the 50-kDa domain of S-1 and the 10-kDa fragment of actin.

Conclusions:

  • Chymotryptically split actin (35-kDa-10-kDa) functionally mimics intact actin in polymerization and myosin binding.
  • The N-terminal 10-kDa fragment of split actin and the 20-kDa domain of S-1 are critical interaction sites.
  • Cross-linking enhances S-1 ATPase activity, suggesting conformational changes induced by specific domain interactions.