Reversible Freeze-Induced β-Sheet-to-Disorder Transition in Aggregated Homopolypeptide System

Abstract

Conformational 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.

Self-assembly of insulin-derived chimeric peptides into two-component amyloid fibrils: the role of Coulombic interactions

“…We used the FF15ipq force field [45] to model aggregated peptides which were solvated with the SPC/E-b model of water molecules [46]. Modeling and docking of ACC1-13K8/ ACC1-13E8 monomers were described previously [18,41,47] assuming an in-register parallel β-sheet architecture of the fibrils enforced by the low symmetry of the constituent building blocks.…”

Bulk Biopolyelectrolyte Complexes from Homopolypeptides: Solid “Salt Bridges”

“…Some work has taken a more materials-like approach and investigated the thermoresponsive properties of these materials, , as well as applications such as drug delivery . Peptide-based materials tend to form secondary structures, such as α-helixes and β-sheets, found in proteins. ,,,− Materials with more solid-like properties have been observed with certain systems. ,, Early work focused on complexes between DNA and copolymers of l -alanine and l -lysine, resulting in B-type DNA patterns superimposed on an α-helix . Moving away from DNA and RNA, mixed systems with one homopolypeptide, such as poly- l -glutamic acid, complexed with oligo­(ethylenimine)­s have been investigated.…”

Impact of Charge Composition and Distribution on the Antibacterial Properties of Polypeptide Coatings

“…The intensities of ω­(NH 3 + ) and ν s (COO – ) bands for the K 5 E 95 -K 19 coating were higher than the K 50 E 50 coating, indicating more E/K residue numbers on the surface. According to the Raman-active amide III band, , the K 5 E 95 -K 19 coating adopted more random-coil conformations than the K 50 E 50 coating (Figure S11).…”