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Reversible Freeze-Induced β‑Sheet-to-Disorder Transition in Aggregated Homopolypeptide System
journal contribution
posted on 2019-10-16, 21:15 authored by Matylda Wacławska, Marcin Guza, Grzegorz Ścibisz, Mateusz Fortunka, Robert Dec, Wojciech Puławski, Wojciech DzwolakConformational
transitions involving aggregated proteins or peptides
are of paramount biomedical and biotechnological importance. Here,
we report an unusual freeze-induced structural reorganization within
a β-sheet-rich ionic coaggregate of poly(l-lysine),
PLL, and poly(l-glutamic acid), PLGA. Freezing aqueous suspensions
of the PLL–PLGA β-aggregate in the presence of low concentrations
of salt (NaBr) induces an instantaneous β-sheet-to-disorder
transition, as probed by infrared spectroscopy in the amide I′
band region. The conformational rearrangement of polypeptide chains
appears to be fully synchronized with the global liquid-to-ice phase
transition. In contrast to the known freeze-induced transitions, the
process described here is fully reversible: the subsequent thawing
results in an instantaneous disorder-to-β-sheet “refolding”.
However, in the absence of traces of soluble salts, the β-sheet
framework of the PLL–PLGA aggregate remains resistant to freezing
as no transition is observed. We note that the occurrence of the transition
depends on the type of salt present in the sample. Our results highlight
a hidden dimension of the structural dynamics within β-sheet-rich
aggregates. Possible scenarios of freeze-induced salt-bridge rupture
and removal of water from nanocanals are discussed.
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PLGAfreeze-induced salt-bridge rupturebiotechnological importanceβ- sheet-richβ- sheet-rich aggregatesPossible scenariosliquid-to-ice phase transitionpolypeptide chainsfreeze-induced transitionsβ- sheet-to-disorder transitionβ- sheet frameworkPLLAggregated Homopolypeptide System Conformational transitionsaggregated proteins
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