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Bundling Process of Citrulline Polypeptides upon UCST-Type Phase Separation
Shota Fujii1, Sotaro Kuroyanagi2, Naohiko Shimada2
1Department of Chemistry and Biochemistry, The University of Kitakyushu, 1-1 Hibikino, Wakamatsu, Kitakyushu-City, Fukuoka 808-0135, Japan.
The Journal of Physical Chemistry. B
|April 21, 2020
Summary
Poly(l-citrulline) (PlOC) exhibits temperature-dependent phase separation, transitioning from alpha-helices to solid-like hexagonal cylinders. This study elucidates the hierarchical aggregation mechanism below its phase separation temperature.
Area of Science:
- Polymer Science
- Biophysical Chemistry
- Materials Science
Background:
- Ureido-modified poly(l-citrulline) (PlOC) displays Upper Critical Solution Temperature (UCST)-type phase separation.
- This behavior occurs under physiologically relevant conditions, with structural transitions from alpha-helix to hexagonal packed cylinders.
- The underlying mechanism of this morphological transformation remains incompletely understood.
Purpose of the Study:
- To investigate the phase separation behavior and hierarchical aggregation mechanism of PlOC.
- To analyze the structural changes occurring below the phase separation temperature (Tp).
Main Methods:
- Small-angle X-ray scattering (SAXS) measurements were employed to study the phase separation.
- The modified unified model was utilized to analyze SAXS data and decompose scattering profiles.
- Analysis focused on identifying structural elements like alpha-helices and their aggregation via hydrogen bonding.
Main Results:
- SAXS analysis revealed temperature-dependent aggregation, classified into three states: mass-fractal (T > Tp), spherical (T < Tp), and micro-order agglomeration.
- Below Tp, PlOC transforms into solid-like aggregates composed of hexagonal packed cylinders.
- The transition from dispersed alpha-helices to hierarchical structures occurs stepwise as temperature decreases below Tp.
Conclusions:
- The study elucidates the stepwise mechanism of PlOC aggregation below its phase separation temperature.
- The observed hierarchical structural transformation resembles protein folding processes.
- Findings provide insights into the self-assembly behavior of PlOC and its potential applications.
