"Wet" Versus "Dry" Folding of Polyproline
Liuqing Shi1, Alison E Holliday2, Brian C Bohrer3
1Department of Chemistry, Indiana University, Bloomington, IN, 47405, USA.
Journal of the American Society for Mass Spectrometry
|April 10, 2016
Summary
Polyproline helices transition between PPI (all-cis) and PPII (all-trans) forms. Solvent-free intermediates refold efficiently into PPI, revealing conserved folding pathways in both solution and vacuum, highlighting water
Area of Science:
- Chemical Physics
- Biophysical Chemistry
- Polymer Science
Background:
- Polyproline helices exist in two main forms: the all-cis polyproline-I (PPI) and the all-trans polyproline-II (PPII) helix.
- The transition between PPI and PPII is influenced by solvent conditions, with PPI favored in 1-propanol and PPII in water.
- Previous studies identified at least six intermediates during the PPI to PPII transition in aqueous solution.
Purpose of the Study:
- To investigate the refolding pathways of PPI-water intermediates in a solvent-free environment.
- To compare the folding mechanisms in solution versus in vacuo.
- To elucidate the role of water in stabilizing specific polyproline conformations.
Main Methods:
- Utilizing solvent-free intermediates generated from the PPI to PPII transition.
- Employing collisional activation in a vacuum to induce refolding.
- Analyzing refolding pathways using principles observed in solution-phase transitions.
Main Results:
- Solvent-free intermediates refold into the PPI helix with high efficiency (>90%).
- The refolding pathways in a solvent-free environment mirror those observed in solution.
- Gentle activation conditions allow some PPII-like structures to form PPII even in a vacuum.
Conclusions:
- The PPI helix is favored under dry conditions, underscoring water's role in promoting the trans proline preference.
- Folding pathways are remarkably conserved between solution-phase (water/propanol) and gas-phase (in vacuo) transitions.
- 1-propanol acts as a mimic of a "dry" environment for polyproline helix folding.
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