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Published on: May 19, 2017
Calcium regulation of an actin spring
Barney K Tam1, Jennifer H Shin, Emily Pfeiffer
1Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Biophysical Journal
|August 19, 2009
Summary
Calcium directly regulates horseshoe crab sperm motility by driving actin bundle extension. Increased calcium concentration enhances extension rate, revealing a novel mechanochemical pathway for cellular movement.
Area of Science:
- Cell Biology
- Biophysics
- Biochemistry
Background:
- Calcium ions (Ca2+) are crucial for numerous cellular processes, including motility.
- The precise mechanisms by which calcium influences motility, such as muscle contraction and neuronal growth, are often indirect and intricate.
- Understanding direct calcium-mediated mechanochemical links is vital for deciphering fundamental biological movements.
Purpose of the Study:
- To establish a direct mechanochemical link between calcium and cellular motility.
- To quantitatively investigate how calcium concentration regulates the dynamics of a primitive motile system.
- To elucidate the molecular mechanism of calcium-driven actin bundle extension.
Main Methods:
- Utilized the actin-based acrosomal bundle of horseshoe crab sperm as a model system.
- Performed experiments to measure bundle extension rates under varying external calcium concentrations.
- Developed theoretical models to explain the observed calcium-dependent dynamics.
Main Results:
- Demonstrated that continuous external calcium is required for acrosomal bundle extension.
- Observed that the extension rate increases with calcium concentration.
- Found that the volumetric rate of extension remains constant at a given calcium concentration.
- Proposed a model where calcium sequentially binds to calmodulin on actin filaments, inducing untwisting and driving extension.
Conclusions:
- Calcium directly and quantitatively regulates the dynamics of the acrosomal bundle in horseshoe crab sperm.
- Calcium-calmodulin binding initiates a wave of actin filament untwisting, a novel mechanism for mechanochemical force generation.
- This study provides a simple, direct model for understanding calcium's role in cellular motility, applicable to more complex systems.
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