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Published on: November 9, 2012
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Persistence length of α-helical poly-L-lysine
Kathryn G Wilcox1, Marlee E Dingle1, Ankit Saha1
1Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH, USA. svetlana.morozova@case.edu.
Soft Matter
|August 30, 2022
Summary
The rigidity of alpha-helices is key to protein structure. This study shows poly-L-lysine (PLL) alpha-helix formation increases its persistence length (lp) from 2 nm to 15-21 nm with rising pH.
Area of Science:
- Biophysics
- Polymer Science
- Protein Structure
Background:
- The alpha-helix is crucial for protein structure and function due to its inherent rigidity.
- Poly-L-lysine (PLL) undergoes a pH-dependent coil-helix transition, making it a model for studying alpha-helical properties.
Purpose of the Study:
- To investigate the persistence length (lp) of alpha-helical poly-L-lysine (PLL) across varying pH and ionic strength.
- To correlate changes in PLL structure with its mechanical properties, specifically persistence length.
Main Methods:
- Light scattering experiments were used to measure radius of gyration (Rg), hydrodynamic radius (Rh), shape factor (Rg/Rh), and second virial coefficient (A2).
- Circular dichroism spectroscopy determined the helical content of PLL.
- Dissipative particle dynamics (DPD) simulations were employed to model PLL behavior.
Main Results:
- Increasing pH from 7.4 to 11.4 induced alpha-helix formation in PLL, significantly increasing its persistence length (lp) from 2 nm to 15-21 nm.
- Experimental findings on lp were corroborated by DPD simulations.
- The measured lp values align with experimental data for alpha-helices, though lower than some molecular dynamics predictions.
Conclusions:
- The persistence length of poly-L-lysine increases dramatically with alpha-helix formation, highlighting the structural contribution of helices.
- Understanding the mechanics of helical polypeptides like PLL provides insights into broader protein mechanics and function.
- This study validates experimental and computational approaches for characterizing polymer mechanics.
