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Related Concept Videos

Assembly of Cytoskeletal Filaments01:18

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...
Formation of Higher-order Actin Filaments01:11

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 Complex Microtubule Structures01:32

Assembly of Complex Microtubule Structures

Complex microtubule structures are present in resting cells and in dividing cells. In resting cells, they are responsible for maintaining the cellular architecture, tracks for intracellular transport, positioning of organelles, assembly of cilia and flagella. They mediate the bipolar spindle assembly for chromosomal segregation and positioning of the cell division plate in dividing cells. The formation of microtubule complex structures depends on the cell type, cell stage, and cell function.
Microtubules in Cell Motility01:24

Microtubules in Cell Motility

Microtubules are thick hollow cylindrical proteins that help form the cytoskeleton. Microtubules have varied roles in the cell. These filaments help form cellular appendages like cilia and flagella, which are responsible for locomotion. The cilia arise from basal bodies, separated from the main body by a membrane-like structure forming the transition zone. This zone is the gate for the entry of lipids and proteins, creating a unique composition of lipids and proteins in the ciliary membrane and...
The Contractile Ring02:15

The Contractile Ring

Contractile rings are composed of microfilaments and are responsible for separating the daughter cells during cytokinesis. Contractile ring assembly proceeds along with other cell cycle events; however, very few mechanistic details are known about the timing and coordination of the contractile rings with the cell cycle.
A small GTPase, RhoA, controls the function and assembly of the contractile ring. RhoA belongs to the Ras superfamily of proteins. The activation of formins by RhoA promotes...
The Contractile Ring02:15

The Contractile Ring

Contractile rings are composed of microfilaments and are responsible for separating the daughter cells during cytokinesis. Contractile ring assembly proceeds along with other cell cycle events; however, very few mechanistic details are known about the timing and coordination of the contractile rings with the cell cycle.
A small GTPase, RhoA, controls the function and assembly of the contractile ring. RhoA belongs to the Ras superfamily of proteins. The activation of formins by RhoA promotes...

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Related Experiment Video

Updated: Jul 8, 2026

Transillumination-Assisted Dissection of Specific Stages of the Mouse Seminiferous Epithelial Cycle for Downstream Immunostaining Analyses
09:59

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Published on: October 7, 2020

Structure of the acrosomal bundle.

Michael F Schmid1, Michael B Sherman, Paul Matsudaira

  • 1National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.

Nature
|September 3, 2004
PubMed
Summary
This summary is machine-generated.

The actin-scruin bundle in Limulus sperm acts as a biological spring, storing elastic energy. Its unique subunit structure allows rapid uncoiling at fertilization to form the acrosomal process.

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Cell Biology

Background:

  • Unactivated Limulus sperm contain a coiled actin-scruin filament bundle.
  • This bundle rapidly extends upon fertilization to form the acrosomal process.

Purpose of the Study:

  • To elucidate the structural basis of the actin-scruin bundle's function as a biological spring.
  • To understand the mechanism of energy storage and release in the acrosomal process.

Main Methods:

  • Electron cryomicroscopy at 9.5-Å resolution.
  • Structural analysis of the extended actin-scruin bundle.

Main Results:

  • The actin-scruin subunits exhibit significant deviations in twist, tilt, and rotation compared to standard F-actin.
  • This structural variability enables the formation of a highly ordered and rigid bundle in the extended state.

Conclusions:

  • The unique structural organization of actin-scruin subunits is key to the filament bundle's ability to store and release elastic energy.
  • This mechanism allows for rapid extension without requiring motor proteins or actin polymerization.