Bioinspired Threonine-Based Polymers with Potent Ice Recrystallization Inhibition Activity

Head-to-Tail Cyclization Enhances Ice-Growth Inhibition by Linear Threonine Oligomers

Developing short antifreeze peptides with low immunogenicity is considered to be a promising strategy for improving cryopreservation. Inspired by the design principles of cyclic peptide drugs characterized by high stability and strong affinity, we propose to use the cyclization strategy as a principle for the design of antifreeze peptides, aiming to enhance their structural stability and ice-binding ability, thereby significantly improving their antifreeze activity. In this study, we choose linear threonine oligomers (L-(Thr)n), composed of common and biocompatible threonine residues, to investigate the mechanism and efficacy of cyclization. Molecular dynamics (MD) simulations are used to compare the ice-growth inhibition ability of a series of linear oligomers and their corresponding cyclic counterparts (49 molecular systems) on different ice planes, resulting in 80.8 μs MD trajectories. A detailed analysis of conformational changes during inhibition and their correlation with inhibitory efficiency reveals that conformational variability is detrimental to the binding of L-(Thr)n to ice, while β-sheet-like conformation has a significant advantage in inhibiting ice growth and is identified as a key factor for the superior performance of cyclized oligomers (C-(Thr)n) over their linear counterparts. Encouragingly, we find that C-(Thr)12 exhibits the most prominent performance, surpassing previously reported cyclic peptides of similar size due to its enhanced structural stability, superior ice binding, coverage, and antiengulfment capabilities. This study provides valuable insights into the design of small-sized ice-growth inhibitors through head-to-tail cyclization of linear oligomers. However, it should be noted that our findings are based purely on computational simulations, and experimental validation in actual cryopreservation conditions remains necessary.

Poly(l-alanine-co-l-threonine succinate) as a Biomimetic Cryoprotectant

We synthesized a series of [(l-Ala)x-co-(l-Thr succinate)y] (PATs), which are analogous to natural antifreezing glycoprotein with the structure of [l-Ala-l-Ala-l-Thr disaccharide]n, by varying the composition and degree of succinylation while fixing their molecular weight (Mn) and Ala/Thr ratio at approximately 10-12 kDa and 2:1, respectively. We investigated their ice recrystallization inhibition (IRI), ice nucleation inhibition (INI), dynamic ice shaping (DIS), thermal hysteresis (TH), and protein cryopreservation activities. Both IRI and INI activities were greater for PATs with higher l-Ala content (PATs-3 and PATs-4) than those with lower l-Ala content (PATs-1 and PATs-2). DIS activity with faceted crystal growth was clearly observed in PATs-2 and PATs-4 with a high degree of succinylation. TH was small with <0.1 °C for all PATs and slightly greater for PATs with a high l-Ala content. Except for PATs-1, the protein (lactate dehydrogenase, LDH) stabilization activity was excellent for all PATs studied, maintaining LDH activity as high as that of fresh LDH even after 15 freeze-thaw cycles. To conclude, the cryo-active biomimetic PATs were synthesized by controlling the l-Ala content and degree of succinylation. Our results showed that PATs with an l-Ala content of 65-70% and degree of succinylation of 12-19% exhibited the cryo-activities of IRI, INI, and DIS, and particularly promising properties for the cryoprotection of LDH protein.

Quantified instant conjugation of peptides on a nanogold surface for tunable ice recrystallization inhibition

The adverse effects of recrystallization limit the application of cryopreservation in many fields. Peptide-based materials play an essential role in the antifreezing area because of their excellent biocompatibility and abundant ice-binding sites. Peptide-gold nanoparticle conjugates can effectively reduce time and material costs through metal-thiol interactions, but controlled modification remains an outstanding issue, which makes it difficult to elucidate the antifreezing effects of antifreeze peptides at different densities and lengths. In this study, we developed an instant peptide capping on gold nanoparticles with butanol-assisted dehydration and provided a controllable quantitative coupling within a certain range. This chemical dehydration makes it possible to fabricate peptide-gold nanoparticle conjugates in large batches at minute levels. Based on this, the influence of the peptide density and sequence length on the antifreezing behaviors of the conjugates was investigated. The results evidenced that the antifreezing property of the flexible peptide conjugated on a rigid core is related to both the density and length of the peptide. In a certain range, the density is proportional to the antifreeze, while the length is negatively correlated with it. We proposed a rapidly controllable method for synthesizing peptide-gold nanoparticle conjugates, which may provide a universal approach for the development of subsequent recrystallization-inhibiting materials.