Cracking the Antifreeze Code: Creating Novel Degradable Antifreeze Polypeptides Offers a New Solution for Cryopreservation

Today, we share a significant study led by Jessica R. Kramer's team, published in Advanced Materials. This research reports a highly potent and cost-effective novel antifreeze polypeptide synthesized from alanine (Ala) and glutamic acid (Glu) via two scalable polymerization methods. At low concentrations (µg mL⁻¹), this polypeptide efficiently inhibits ice recrystallization (IRI), demonstrating activity comparable to natural fish antifreeze proteins. It also possesses excellent properties including good biocompatibility, biodegradability, and thermal reversibility. The study further confirms that this polypeptide effectively protects the activity of model protein therapeutics (e.g., lactate dehydrogenase, antibodies) during repeated freeze-thaw cycles and can inhibit ice crystal coarsening in frozen foods, showcasing broad application prospects in biomedicine and the food industry.

Figure 1. Design and synthesis of antifreeze polymer panel.

01 Research Background

The formation and growth of ice crystals pose a common challenge across many fields, including construction materials, transportation, agriculture, food, and biomedicine. While widely used small-molecule antifreeze agents like ethylene glycol are effective, they are toxic to mammalian cells and pose environmental risks. In biomedicine (e.g., cell and protein cryopreservation), commonly used agents like dimethyl sulfoxide (DMSO) and glycerol also exhibit significant cytotoxicity. The food industry often uses polysaccharides like carrageenan to improve ice crystal morphology, but these typically require high concentrations (e.g., 200 mg mL⁻¹), leading to high solution viscosity and potential osmotic pressure issues. In nature, organisms such as polar fish have evolved antifreeze (glyco)proteins (AF(G)Ps) to address this challenge; they can specifically bind to ice crystals and inhibit their growth at very low concentrations. However, extracting or recombinantly expressing AF(G)Ps from organisms is extremely costly, limiting their large-scale application. Therefore, developing an efficient, safe, economical, and scalable antifreeze material is urgently needed.

02 Innovative Highlights

Innovative Molecular Design: Biomimetic Simplification Focused on Natural Amino Acids

Drawing inspiration from natural alanine-rich Type I antifreeze protein (AFP1) and antifreeze glycoprotein (AFGP), the research team abandoned complex glycosylation or specific sequences, utilizing only the two most basic and economical natural amino acids—Ala and Glu. Through statistical copolymerization, they obtained sequence-simplified (Ala-Glu)ₙ polypeptides, retaining the key function (interaction of Ala's hydrophobic methyl group with ice) while ensuring water solubility via Glu's hydrophilic side chain.

Establishing a Green Synthesis Pathway Involving Aqueous Phase Without Protecting Groups

The study compared two N-carboxyanhydride (NCA) ring-opening polymerization methods: Method A used a (PMe₃)₄Co catalyst, which, although requiring anhydrous/anaerobic conditions and protecting groups (e.g., tBu for Glu), enabled precise synthesis of long-chain polypeptides up to 200 amino acids with a narrow molecular weight distribution (Đ = 1.11–1.16). Method B used a hexylamine initiator, operable under ambient atmosphere in DMF/water mixed solvent without protecting groups, greatly simplifying the process and reducing cost and environmental burden, although the chain length was limited to about 50 amino acids.

Clarifying α-Helical Conformation as the Key to Antifreeze Activity

By systematically varying the polypeptide's chain length, chirality (L- vs. D-form), charge (anionic Glu vs. cationic Lys), and hydrophobic residue (Ala vs. Val), and combining circular dichroism (CD) spectroscopy with ice recrystallization inhibition (IRI) assays, the study clearly demonstrated for the first time that the α-helical conformation of the (Ala-Glu)ₙ polypeptide is the structural basis for its high antifreeze activity, while chirality has no effect. Racemic polypeptides with random coil conformations completely lost activity.

Validating Practical Utility in Biomedicine and Food Sectors

Going beyond mere activity characterization, the research conducted in-depth assessments of cytotoxicity and biodegradability, and performed two proof-of-concept experiments: protein freeze-thaw protection and food ice crystal control, fully demonstrating the practical application potential of this next-generation antifreeze agent.

03 Results and Discussion

3.1 Successful Polypeptide Synthesis and Structural Characterization

The research team successfully synthesized (Ala-Glu)ₙ polypeptides. Fourier-transform infrared (FTIR) spectroscopy showed that after polymerization, the characteristic peaks of the NCA monomers (1856 and 1779 cm⁻¹) disappeared, and characteristic absorptions for amide I (1656 cm⁻¹) and II (1546 cm⁻¹) bands appeared, confirming peptide bond formation.

Circular dichroism (CD) analysis indicated that (Ala-Glu)ₙ polypeptides in PBS buffer exhibited a typical right-handed α-helical conformation with negative Cotton effects at 208 nm and 222 nm. Helical stability increased with chain length, and this conformation could fully recover after heating to 95°C, demonstrating excellent thermal reversibility, crucial for industrial applications requiring heat treatment.

Figure 2. Polypeptide structural characterization.

3.2 Exceptional Antifreeze Activity and Structure-Activity Relationship Analysis

The ice recrystallization inhibition (IRI) assay (splat assay) was the core validation. Results showed that (Ala-Glu)₅₀ and (Ala-Glu)₂₀₀, at concentrations as low as 100 µg mL⁻¹, could inhibit over 90% of ice crystal growth, matching the effect of natural winter flounder antifreeze protein (wfAFP1) and far surpassing 10% DMSO.

By comparing polypeptides with different structures, the researchers revealed a clear structure-activity relationship:

Chain Length Effect:​ Activity increased significantly from the 30-mer to the 50-mer, then plateaued, indicating that approximately 50 amino acids are sufficient to form an effective ice-binding interface.

Conformation is Crucial:​ The L-form (Ala-Glu)₅₀ and its mirror-image D-form (Ala-Glu)₅₀, both possessing α-helical structures, showed comparable activity. In contrast, conformationally disordered racemic polypeptides (Ala-D/L-Glu-D/L)₅₀ were completely inactive even at 10 times the concentration, proving that the helical conformation itself is more important than specific chirality.

Residue Specificity:​ Replacing Ala with Val (Valine) reduced helicity and halved activity, indicating that the size and arrangement of Ala's methyl group confer a unique advantage for binding to the ice surface.

Dynamic ice crystal morphology experiments further showed that (Ala-Glu)₅₀ could shape ice crystals into hexagonal plates, consistent with the behavior of natural antifreeze proteins binding to prismatic ice planes.

Figure 3. Antifreeze activity assays.

3.3 Excellent Biocompatibility, Degradability, and Protein Protection Efficacy

Cytotoxicity assays (CCK-8 method) showed that the anionic (Ala-Glu)₇₅ caused no significant toxicity to human embryonic kidney cells (HEK 293) even at high concentrations up to 2 mg mL⁻¹. In contrast, the cationic control (Ala-Lys)₇₅ showed concentration-dependent toxicity, highlighting the safety of (Ala-Glu)ₙ.

Enzymatic degradation experiments proved that L-polypeptides could be effectively degraded by proteinase K and pepsin, whereas D-mirror-image polypeptides resisted degradation. This provides options for applications with different lifespan requirements (e.g., degradable biomedical carriers vs. long-lasting industrial coatings).

In proof-of-concept tests, (Ala-Glu)₅₀ significantly protected lactate dehydrogenase (LDH) activity after 8 freeze-thaw cycles, achieving complete protection at 100 µg mL⁻¹. Similarly, it effectively prevented functional loss of anti-enhanced green fluorescent protein antibody (aEGFP) during freeze-thaw processes.

3.4 Application Demonstration in a Food Model

Adding (Ala-Glu)₅₀ to commercial ice cream, IRI experiments clearly showed that ice crystal size in treated samples was significantly smaller than in untreated controls, demonstrating its direct application potential for improving the texture of frozen foods.

04 Conclusion and Future Perspectives

This study successfully developed a class of biomimetic antifreeze polypeptides based on Ala and Glu. Its core value lies in achieving efficient ice crystal control comparable to natural antifreeze proteins through an extremely simplified molecular design (using only two natural amino acids) and a green, economical synthesis process. This polypeptide combines multiple advantages: high efficiency, safety, biodegradability/customizable longevity, and thermal stability. The significant importance of this work is its successful balance of the core contradiction in materials development: performance, safety, and cost. The emergence of (Ala-Glu)ₙ polypeptides makes it possible to use efficient, non-toxic antifreeze agents in large-scale applications such as biomedicine (e.g., cryopreservation of advanced cells/tissues/organs, protein drug formulations), the food industry (improving the quality of ice cream, frozen dough, etc.), and even agricultural coatings. Future research could focus on: further exploring the detailed mechanisms of its interaction with different biomacromolecules (e.g., cell membranes); advancing its standardized study in the cryopreservation of clinical-grade cell therapy products; and exploring its synergistic effects with other cryoprotectants. In summary, this research provides a powerful and versatile new tool platform to address the widespread challenge of freezing damage.

Original Article：

McPartlon TJ, Osborne CT, Wang K, Detwiler RE, Meister K, Kramer JR. An Ultrapotent, Ultraeconomical, Antifreeze Polypeptide. Adv Mater. 2026 Jan;38(4):e20504. 

https://advanced.onlinelibrary.wiley.com/doi/10.1002/adma.202420504