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The force-driven conformations of heparin studied with single molecule force microscopy
Piotr E Marszalek1, Andres F Oberhauser, Hongbin Li
1Department of Mechanical Engineering and Material Sciences, Duke University, Durham, North Carolina 27708 USA.
Biophysical Journal
|September 26, 2003
Summary
Heparin chains act as simple springs until stretched to 200 pN, where sugar rings flip, causing enthalpic elasticity. This mechanical response may regulate ligand binding in biological processes.
Area of Science:
- Biophysics
- Biochemistry
- Materials Science
Background:
- Heparin is a crucial glycosaminoglycan involved in numerous biological processes.
- Understanding heparin's mechanical properties is essential for elucidating its biological functions.
- Previous studies have not fully characterized heparin's response to mechanical force at the single-molecule level.
Purpose of the Study:
- To investigate the mechanical response of single heparin chains to stretching.
- To identify the molecular mechanisms underlying heparin's elasticity.
- To explore the biological implications of heparin's mechanical properties.
Main Methods:
- Single molecule force spectroscopy (SMFS) was employed to stretch individual heparin chains.
- Atomic force microscopy (AFM) was utilized to measure the force-extension relationship.
- Analysis of force-extension curves to determine entropic and enthalpic contributions to elasticity.
Main Results:
- Below 200 piconewtons (pN), heparin behaves as a passive entropic spring.
- At approximately 200 pN, a significant enthalpic elasticity plateau was observed.
- This plateau is attributed to the flipping of heparin's sugar rings into more energetic, extended conformations.
Conclusions:
- Heparin exhibits distinct mechanical behaviors at different force regimes.
- Conformational transitions in heparin's sugar rings are responsible for its enthalpic elasticity.
- These force-induced transitions likely play a role in regulating ligand binding in vivo, impacting processes like exocytosis and cell-matrix interactions.