'Antifreeze' glycoproteins from polar fish

Polyvinyl alcohol addition to freezing extender can improve the post-thaw quality, longevity and in vitro fertility of ram epididymal spermatozoa

Recovering and cryopreserving epididymal spermatozoa are suitable methods for preserving the genetic potential of livestock and endangered species. Regarding encouraging reports on the use of polyvinyl alcohol (PVA) in cryopreserving various cell types, we conducted this study to examine the impact of PVA on the post-thaw quality, longevity, and in vitro fertility of ram epididymal sperm. In the first experiment, ram epididymal spermatozoa were frozen in extenders containing 6 % glycerol and 0, 0.5, 1, 2, 5, 10, or 15 mg/ml of PVA. Polyvinyl alcohol at concentrations of 0.5, 1, and 2 mg/ml improved the motility and functional membrane integrity (FMI) of the sperm compared with the control group (P < 0.05). In the second experiment, we investigated whether PVA could partially substitute glycerol in the freezing extender. PVA was added at 0, 0.5, 1, and 2 mg/ml to the extenders containing 1 % or 2 % glycerol. After thawing, the sperm motility parameters of the group containing 1 mg/ml PVA and 2 % glycerol were significantly higher than those of the un-supplemented groups (P < 0.05). In the third experiment, the effect of PVA on the post-thaw sperm longevity were examined. Sperm were frozen in 3 extenders: one containing 6 % glycerol and 1 mg/ml PVA (Gly6P1), another containing 2 % glycerol and 1 mg/ml PVA (Gly2P1), and a control extender with 6 % glycerol. After thawing, the quality of the sperm was evaluated. Sperm were then diluted in human tubal fluid (HTF) and incubated at 37 °C for 3 h. Afterwards, the quality of the sperm was evaluated once more. The presence of PVA in the freezing extender improved motility parameters and FMI. Additionally, PVA-containing groups had lower proportions of capacitated and acrosome reacted sperm compared with the control group (P < 0.05). The Gly6P1 group performed better than the other two groups (P < 0.05). In the fourth experiment, sperm from the Gly6P1 and Control groups were used in the IVF process immediately after thawing (T0) and after a 3-h incubation at 37 °C in HTF (T3). Cleavage, blastocyst and hatching rates in both groups were similar at T0, but they were lower in the Control group at T3 (P < 0.05). In conclusion, PVA as an additive to the freezing extender significantly improves post-thaw motility, viability, acrosome integrity, longevity, and fertile lifespan of ram epididymal spermatozoa.

Self-assembling peptides: Perspectives regarding biotechnological applications and vaccine development

Self-assembly involves a set of molecules spontaneously interacting in a highly coordinated and dynamic manner to form a specific supramolecular structure having new and clearly defined properties. Many examples of this occur in nature and many more came from research laboratories, with their number increasing every day via ongoing research concerning complex biomolecules and the possibility of harnessing it when developing new applications. As a phenomenon, self-assembly has been described on very different types of molecules (biomolecules including), so this review focuses on what is known about peptide self-assembly, its origins, the forces behind it, how the properties of the resulting material can be tuned in relation to experimental considerations, some biotechnological applications (in which the main protagonists are peptide sequences capable of self-assembly) and what is yet to be tuned regarding their research and development.

Physiological, metabolomic, and transcriptomic reveal metabolic pathway alterations in Gymnocypris przewalskii due to cold exposure

Teleost fish have evolved various adaptations that allow them to tolerate cold water conditions. However, the underlying mechanism of this adaptation is poorly understood in Tibetan Plateau fish. RNA-seq combined with liquid chromatography‒mass spectrometry (LC‒MS/MS) metabolomics was used to investigate the physiological responses of a Tibetan Plateau-specific teleost, Gymnocypris przewalskii, under cold conditions. The 8-month G. przewalskii juvenile fish were exposed to cold (4 ℃, cold acclimation, CA) and warm (17 ℃, normal temperature, NT) temperature water for 15 days. Then, the transcript profiles of eight tissues, including the brain, gill, heart, intestine, hepatopancreas, kidney, muscle, and skin, were evaluated by transcriptome sequencing. The metabolites of the intestine, hepatopancreas, and muscle were identified by LC‒MS/MS. A total of 5,745 differentially expressed genes (DEGs) were obtained in the CA group. The key DEGs were annotated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis. The DEGs from the eight tissues were significantly enriched in spliceosome pathways, indicating that activated alternative splicing is a critical biological process that occurs in the tissues to help fish cope with cold stress. Additionally, 82, 97, and 66 differentially expressed metabolites were identified in the intestine, hepatopancreas, and muscle, respectively. Glutathione metabolism was the only overlapping significant pathway between the transcriptome and metabolome analyses in these three tissues, indicating that an activated antioxidative process was triggered during cold stress. In combination with the multitissue transcriptome and metabolome, we established a physiology-gene‒metabolite interaction network related to energy metabolism during cold stress and found that gluconeogenesis and long-chain fatty acid metabolism played critical roles in glucose homeostasis and energy supply.

Marine glycoproteins: a mine of their structures, functions and potential applications

Many bioactive compounds are reported from marine organisms, which are significantly different from those found in terrestrial organisms regarding their chemical structures and pharmacological activities. Marine glycoproteins (MGs) have aroused increasing attention as a good nutrient source owing to their potential applications in medicine, cosmetics and food. However, there is a lack of a comprehensive study on MGs to help readers understand the current state of research on marine-derived glycoproteins. The current review compiles the recent progress made on the structures and functions of MGs with future perspectives to maximize their value and applications via bibliometric analysis methods for the first time. The current research on MGs appears mostly limited to the laboratory, with no large-scale production of marine glycoproteins developed. The sugar chains are bound to proteins through covalent bonds that can readily be cleaved leading to difficultly in their separation and purification. Health effects attributed to MGs include treatment of inflammatory diseases, as well as anti-oxidant, immune modulation, anti-tumor, hypolipidemic, hypoglycemic, anti-bacterial and anti-freeze activities. This review can not only deepen the understanding of the functions of MGs, but also lay an important foundation for the further development and utilization of marine resources.

Mechanism of Binding of Polyproline to Ice via Interfacial Water: An Experimental and Theoretical Study

The molecular mechanism underlying inhibition of ice growth by polyproline (PPro), a minimal antifreeze glycoprotein mimic, remains unclear. In this work, the change in the structure of water during the growth of ice in PPro solutions was investigated using a combination of near-infrared spectroscopy and molecular dynamics (MD) simulations. The results show that only high concentrations of PPro solutions can effectively inhibit ice growth, as indicated by the variation in the spectral intensity of ice with time. When PPro exhibits an antifreeze effect, the spectral intensity of hydrated water associated with PPro in a solution is weakened. The experiments and MD simulations reveal that the quantity of the interfacial water between the ice crystal and the hydrophobic groups of PPro progressively reaches a plateau. Most significantly, we present clear evidence that the stable existence of this interfacial water is critical for the antifreeze activity of PPro.

Antifreeze protein type III addition to freezing extender comprehensively improves post-thaw sperm properties in Okinawan native Agu pig

Sperm cryopreservation often leads to physical cell damage through ice crystal formation. This study evaluates the improvements to freezing extender cryoprotective activity due to antifreeze protein (AFP) addition, which primarily acts on ice crystal formation, through investigating the post-thaw sperm properties of Okinawan native Agu pig. Six individual boar sperm samples were diluted with the freezing extender supplemented with 1 μg/mL of AFP I or AFP III and then subjected to cryopreservation. Treatment with AFP I during the freezing procedure had no improvement for any characteristics after thawing compared to untreated sperm. In contrast, the addition of AFP III to the freezing extender strongly increased sperm motility, mitochondria and cell membrane integrity, and the acrosomal proteolytic activity of frozen-thawed sperm in 5 of 6 individuals (P < 0.05). Furthermore, cryoinjury prevention by AFP III significantly enhanced sperm viability (by ATP content), and maintained DNA quality and in vitro sperm penetrability compared with AFP I treatment (P < 0.05). These findings demonstrate that AFP III addition to the freezing extender of boar sperm is more effective in maintaining sperm characteristics than the extender without AFP III or AFP I, despite individual differences in response.

Mitochondrial Haemoglobin Is Upregulated with Hypoxia in Skeletal Muscle and Has a Conserved Interaction with ATP Synthase and Inhibitory Factor 1

The globin protein superfamily has diverse functions. Haemoglobin has been found in non-erythroid locations, including within the mitochondria. Using co-immunoprecipitation and in silico methods, we investigated the interaction of mitochondrial haemoglobin with ATP synthase and its associated proteins, including inhibitory factor 1 (IF1). We measured the expression of mitochondrial haemoglobin in response to hypoxia. In vitro and in silico evidence of interactions between mitochondrial haemoglobin and ATP synthase were found, and we report upregulated mitochondrial haemoglobin expression in response to hypoxia within skeletal muscle tissue. Our observations indicate that mitochondrial pH and ATP synthase activity are implicated in the mitochondrial haemoglobin response to hypoxia.

Effects of Antifreeze Protein Type I and Glycerol in Diluents on Cryopreserved Goat Epididymal Sperm

The effect of antifreeze protein (AFP) as a cryoprotectant used in different concentrations of glycerol on post-thaw quality of epididymal sperm was investigated. Sperm were isolated from 50 testicles, obtained from 25 healthy mature goat bucks, with progressive motility >80%, and total morphological abnormalities <10% were pooled in each replication. The semen samples were diluted with Tris-citrate-fructose-soybean lecithin extender containing different concentration of AFP [0 μg/mL (A0), 5 μg/mL (A5), 10 μg/mL (A10)]. Each concentration of AFP was added in an extender containing either 7% (G7) or 5% (G5) glycerol. Post-thaw total and progressive motility were found to be higher (p < 0.05) in groups A5G5 and A5G7. Plasma membrane integrity, sperm acrosome integrity, DNA integrity, acrosome intact sperm, and mitochondrial membrane potential were found to be higher (p < 0.05) in groups A5G5 and A10G5. Sperm viability was found to be higher (p < 0.05) in group A5G5, while lipid peroxidation was recorded lower (p < 0.05) in groups A5G5 and A5G7. Regarding the apoptosis occurrence, the results demonstrate higher (p < 0.05) live post-thawed spermatozoa for groups containing 5 μg/mL AFP with 5% and 7% glycerol in addition to the lowest (p < 0.05) value for groups containing 0 μg/mL AFP with 5% and 7% glycerol. Based on these results, the present study concludes that the addition of 5 μg/mL AFP in combination with 5% glycerol in freezing extender improves the post-thaw quality, structure, and function parameters for buck spermatozoa.

Regulating Antifreeze Activity through Water: Latent Functions of the Sugars of Antifreeze Glycoprotein Revealed by Total Chemical Synthesis

Antifreeze glycoprotein (AFGP), which inhibits the freezing of water, is highly O-glycosylated with a disaccharide, d-Galβ1-3-d-GalNAcα (GalGalNAc). To elucidate the function of the sugar residues for antifreeze activity at the molecular level, we conducted a total chemical synthesis of partially sugar deleted AFGP derivatives, and unnatural forms of AFGPs incorporating glucose (Glc)-type sugars instead of galactose (Gal)-type sugars. These elaborated AFGP derivatives demonstrated that the stereochemistry of each sugar residue on AFGPs precisely correlates with the antifreeze activity. A hydrogen-deuterium exchange experiment using synthetic AFGPs revealed a different dynamic behavior of water around sugar residues depending on the sugar structures. These results indicate that sugar residues on AFGP form a unique dynamic water phase that disturbs the absorbance of water molecules onto the ice surface, thereby inhibiting freezing.

The Effects of Different Doses of ROCK Inhibitor, Antifreeze Protein III, and Boron Added to Semen Extender on Semen Freezeability of Ankara Bucks

In the presented study, the effects of ROCK inhibitor Y-27632, antifreeze protein III, and boron at two different doses were investigated on the spermatological parameters of Ankara buck semen after freeze−thawing. Ejaculates were collected from bucks using an electroejaculator during the breeding season. The ejaculates that showed appropriate characteristics were pooled and used in the dilution and freezing of semen. The extender groups were formed by adding two different doses of three different additives (ROCK inhibitor Y-27632, 5 and 20 µM; antifreeze protein III, 1 and 4 µg/mL; boron, 0.25 and 1 mM) to the control extender. The semen was diluted with the different extenders at 35−37 °C and loaded into straws. Sperm samples frozen in liquid nitrogen vapors, following equilibration, were stored in liquid nitrogen. It was observed that extender supplementation improved post-thaw motility of Ankara buck semen after freeze−thawing. Differences were significant (p < 0.01) for 5 and 10 µM doses of ROCK inhibitor (71.82% and 74.04 % motility), as well as for 0.25 and 1 mM doses of boron (76.36% and 72.08% motility), compared to the control group (66.15% motility). With respect to the evaluation of acrosomal integrity and mitochondrial activity after freeze−thawing, although supplementation provided protection at all doses, the efficacy was not statistically significant (p > 0.05). It was observed that DNA damage was improved by antifreeze protein III at 1 µg/mL (1.23% ± 0.23%) and by boron at all doses (0.25 mM: 1.83% and 1 mM: 1.18%) compared to the control group (3.37%) (p < 0.01), following the thawing process. In the present study, it was determined that some additives added to the extender provided significant improvements in buck spermatozoa motility and DNA damage after thawing.

The Modification of Polyvinyl Alcohol for Ice Nucleation Based upon the Structures of Antifreeze Glycoproteins Found in Antarctic Fish

Various alternative compounds have been investigated to prevent icing, one of which includes poly(vinyl) alcohol (PVA), which has shown promising anti-freeze effects. However, determining the optimal structures and formulations of PVA for anti-icing applications has remained a challenge. Building upon our previous work, which used molecular dynamics simulations to assess the effects of hydroxyl group separation distance on ice nucleation, in this work, PVA was modified based upon the structures of antifreeze glycoproteins (AFGPs) found in Antarctic fish, and examined as a potential antifreeze compound. Four different PVA samples with different degrees of hydrolysis were fabricated and subsequently examined for their effects on ice crystallization. The results showed that the modified PVA samples with degrees of hydrolysis of 76% and 66% had an effect on ice crystallization, delaying ice crystallization by an average of approximately 20 min, and even preventing ice crystallization altogether in a small portion of the sample. Meanwhile, other samples with degrees of hydrolysis of 100% and 34% either showed no effect on ice crystallization, shortened the ice crystallization time, and appeared to promote ice nucleation.

Peptide-DNA origami as a cryoprotectant for cell preservation

Cryopreservation of cells is essential for the conservation and cold chain of bioproducts and cell-based medicines. Here, we demonstrate that self-assembled DNA origami nanostructures have a substantial ability to protect cells undergoing freeze-thaw cycles; thereby, they can be used as cryoprotectant agents, because their nanoscale morphology and ice-philicity are tailored. In particular, a single-layered DNA origami nanopatch functionalized with antifreezing threonine peptides enabled the viability of HSC-3 cells to reach 56% after 1 month of cryopreservation, surpassing dimethyl sulfoxide, which produced 38% viability. It also exhibited minimal dependence on the cryopreservation period and freezing conditions. We attribute this outcome to the fact that the peptide-functionalized DNA nanopatches exert multisite actions for the retardation of ice growth in both intra- and extracellular regions and the protection of cell membranes during cryopreservation. This discovery is expected to deepen our fundamental understanding of cell survival under freezing environment and affect current cryopreservation technologies.

Cold adaptation strategies in plants—An emerging role of epigenetics and antifreeze proteins to engineer cold resilient plants

Cold stress adversely affects plant growth, development, and yield. Also, the spatial and geographical distribution of plant species is influenced by low temperatures. Cold stress includes chilling and/or freezing temperatures, which trigger entirely different plant responses. Freezing tolerance is acquired via the cold acclimation process, which involves prior exposure to non-lethal low temperatures followed by profound alterations in cell membrane rigidity, transcriptome, compatible solutes, pigments and cold-responsive proteins such as antifreeze proteins. Moreover, epigenetic mechanisms such as DNA methylation, histone modifications, chromatin dynamics and small non-coding RNAs play a crucial role in cold stress adaptation. Here, we provide a recent update on cold-induced signaling and regulatory mechanisms. Emphasis is given to the role of epigenetic mechanisms and antifreeze proteins in imparting cold stress tolerance in plants. Lastly, we discuss genetic manipulation strategies to improve cold tolerance and develop cold-resistant plants.

Red Blood Cell Cryopreservation with Minimal Post-Thaw Lysis Enabled by a Synergistic Combination of a Cryoprotecting Polyampholyte with DMSO/Trehalose

From trauma wards to chemotherapy, red blood cells are essential in modern medicine. Current methods to bank red blood cells typically use glycerol (40 wt %) as a cryoprotective agent. Although highly effective, the deglycerolization process, post-thaw, is time-consuming and results in some loss of red blood cells during the washing procedures. Here, we demonstrate that a polyampholyte, a macromolecular cryoprotectant, synergistically enhances ovine red blood cell cryopreservation in a mixed cryoprotectant system. Screening of DMSO and trehalose mixtures identified optimized conditions, where cytotoxicity was minimized but cryoprotective benefit maximized. Supplementation with polyampholyte allowed 97% post-thaw recovery (3% hemolysis), even under extremely challenging slow-freezing and -thawing conditions. Post-thaw washing of the cryoprotectants was tolerated by the cells, which is crucial for any application, and the optimized mixture could be applied directly to cells, causing no hemolysis after 1 h of exposure. The procedure was also scaled to use blood bags, showing utility on a scale relevant for application. Flow cytometry and adenosine triphosphate assays confirmed the integrity of the blood cells post-thaw. Microscopy confirmed intact red blood cells were recovered but with some shrinkage, suggesting that optimization of post-thaw washing could further improve this method. These results show that macromolecular cryoprotectants can provide synergistic benefit, alongside small molecule cryoprotectants, for the storage of essential cell types, as well as potential practical benefits in terms of processing/handling.

Site-Specific Water Dynamics in the First Hydration Layer of an Anti-Freeze Glyco-Protein: A Simulation Study

Antifreeze glycoproteins (AFGPs) inhibit ice recrystallization by a mechanism remaining largely elusive. Dynamics of AFGPs’ hydration water and its involvement in the antifreeze activity, for instance, have not been identified...

Diffusion Attachment Model for Long Helical Antifreeze Proteins to Ice

Some of the most potent antifreeze proteins (AFPs) are approximately rigid helical structures that bind with one side in contact with the ice surface at specific orientations. These AFPs take random orientations in solution; however, most orientations become sterically inaccessible as the AFP approaches the ice surface. The effect of these inaccessible orientations on the rate of adsorption of AFP to ice has never been explored. Here, we present a diffusion-controlled theory of adsorption kinetics that accounts for these orientational restrictions to predict a rate constant for adsorption (k_on, in m/s) as a function of the length and width of the AFP molecules. We find that k_on decreases with length and diameter of the AFP and is almost proportional to the inverse of the area of the binding surface. We demonstrate that the restricted orientations create an entropic barrier to AFP adsorption, which we compute to be approximately 7 k_BT for most AFPs and up to 9 k_BT for Maxi, the largest known AFP. We compare the entropic resistance 1/k_on to resistances for diffusion through boundary layers and across typical distances in the extracellular matrix and find that these entropic and diffusion resistances could become comparable in the small confined spaces of biological environments.

Sequence and structure comparison of ATP synthase F0 subunits 6 and 8 in notothenioid fish

Mitochondrial changes such as tight coupling of the mitochondria have facilitated sustained oxygen and respiratory activity in haemoglobin-less icefish of the Channichthyidae family. We aimed to characterise features in the sequence and structure of the proteins directly involved in proton transport, which have potential physiological implications. ATP synthase subunit a (ATP6) and subunit 8 (ATP8) are proteins that function as part of the F0 component (proton pump) of the F0F1complex. Both proteins are encoded by the mitochondrial genome and involved in oxidative phosphorylation. To explore mitochondrial sequence variation for ATP6 and ATP8 we analysed sequences from C. gunnari and C. rastrospinosus and compared them with their closely related red-blooded species and eight other vertebrate species. Our comparison of the amino acid sequence of these proteins reveals important differences that could underlie aspects of the unique physiology of the icefish. In this study we find that changes in the sequence of subunit a of the icefish C. gunnari at position 35 where there is a hydrophobic alanine which is not seen in the other notothenioids we analysed. An amino acid change of this type is significant since it may have a structural impact. The biology of the haemoglobin-less icefish is necessarily unique and any insights about these animals will help to generate a better overall understanding of important physiological pathways.

Computational Assessment of Modified Antifreeze Glycoproteins on Ice Nucleation

Antifreeze glycoproteins (AFGPs) found in various fish are used by the organisms to prevent freezing. While these compounds have been studied for their ability to bind to, and prevent the complete crystallization of water, the exact mechanisms by which AFGPs prevent freezing are still undetermined. Therefore, building upon our previous work, this study uses molecular dynamics simulations to assess the effects of hydroxyl group separation distance on AFGP ice nucleation activity. Water droplet crystallization simulations showed that modified AFGP structures containing hydroxyl distances smaller than ~3.0 Å lost their ability to prevent ice crystallization. Furthermore, modified AFGP containing hydroxyl distances of 7.327 Å and 6.160 Å was correlated with a promotion in ice nucleation, as demonstrated by the changes in the energy of the system. This supports the notion that the distance, and therefore, geometry characteristics between the hydroxyl groups located on the saccharide structures play a key role in the ice crystallization inhibition properties of AFGP compounds.

Advanced Nanomaterials-Assisted Cell Cryopreservation: A Mini Review

Cell cryopreservation is of vital significance both for transporting and storing cells before experimental/clinical use. Cryoprotectants (CPAs) are necessary additives in the preserving medium in cryopreservation, preventing cells from freeze-thaw injuries. Traditional organic solvents have been widely used in cell cryopreservation for decades. Given the obvious damage to cells due to their undesirable cytotoxicity and the burdensome post-thaw washing cycles before use, traditional CPAs are more and more likely to be replaced by modern ones with lower toxicity, less processing, and higher efficiency. As materials science thrives, nanomaterials are emerging to serve as potent vehicles for delivering nontoxic CPAs or inherent CPAs comparable to or even superior to conventional ones. This review will introduce some advanced nanomaterials (e.g., organic/inorganic nanoCPAs, nanodelivery systems) utilized for cell cryopreservation, providing broader insights into this developing field.

Use of Ice Recrystallization Inhibition Assays to Screen for Compounds That Inhibit Ice Recrystallization

Ice recrystallization inhibition assays are used to screen for compounds that possess the ability to inhibit ice recrystallization. The most common of these assays are the splat cooling assay (SCA) and sucrose sandwich assay (SSA). These two assays possess similarities; however, they vary in their sample size, cooling rate, and the solution used to dissolve the analyte. In this chapter, both assay methods are described in detail, and we perform a direct comparison of the assays by evaluating the IRI activity of an antifreeze protein (AFP I). IRI activity is quantified by using ImageJ software to analyze ice crystals, and a quantitative value describing the efficiency of the inhibitor is generated. This analysis emphasizes the importance of choosing the right assay to measure IRI activity.

Hypothermic preservation of rat hearts using antifreeze glycoprotein

Antifreeze proteins are an effective additive for low-temperature preservation of solid organs. Here, we compared static hypothermic preservation with and without antifreeze glycoprotein (AFGP), followed by nonfreezing cryopreservation of rat hearts. The heart was surgically extracted and immersed in one of the cardioplegia solutions after cardiac arrest. Control rat hearts (n=6) were immersed in University of Wisconsin (UW) solution whereas AFGP-treated hearts (AFGP group) (n=6) were immersed in UW solution containing 500 ?g/ml AFGP. After static hypothermic preservation, a Langendorff apparatus was used to reperfuse the coronary arteries with oxygenated Krebs-Henseleit solution. After 30, 60, 90, and 120 min, the heart rate (HR), coronary flow (CF), cardiac contractile force (max dP/dt), and cardiac diastolic force (min dP/dt) were measured. Tissue water content (TWC) and tissue adenosine triphosphate (ATP) levels in the reperfused preserved hearts were also assessed. All the parameters were compared between the control and AFGP groups. Compared with the control group, the AFGP group had significantly (p<0.05) higher values of the following parameters: HR at 60, 90, and 120 min; CF at all four time points; max dP/dt at 90 min; min dP/dt at 90 and 120 min; and tissue ATP levels at 120 min. TWC did not differ significantly between the groups. The higher HR, CF, max dP/dt, min dP/dt, and tissue ATP levels in the AFGP compared with those in control hearts suggested that AFGP conferred superior hemodynamic and metabolic functions. Thus, AFGP might be a useful additive for the static/nonfreezing hypothermic preservation of hearts.

Antifreeze Proteins and Their Practical Utilization in Industry, Medicine, and Agriculture

Antifreeze proteins (AFPs) are specific proteins, glycopeptides, and peptides made by different organisms to allow cells to survive in sub-zero conditions. AFPs function by reducing the water’s freezing point and avoiding ice crystals’ growth in the frozen stage. Their capability in modifying ice growth leads to the stabilization of ice crystals within a given temperature range and the inhibition of ice recrystallization that decreases the drip loss during thawing. This review presents the potential applications of AFPs from different sources and types. AFPs can be found in diverse sources such as fish, yeast, plants, bacteria, and insects. Various sources reveal different α-helices and β-sheets structures. Recently, analysis of AFPs has been conducted through bioinformatics tools to analyze their functions within proper time. AFPs can be used widely in various aspects of application and have significant industrial functions, encompassing the enhancement of foods’ freezing and liquefying properties, protection of frost plants, enhancement of ice cream’s texture, cryosurgery, and cryopreservation of cells and tissues. In conclusion, these applications and physical properties of AFPs can be further explored to meet other industrial players. Designing the peptide-based AFP can also be done to subsequently improve its function.

Glycopeptide drugs: A pharmacological dimension between "Small Molecules" and "Biologics"

Peptides are an important class of molecules with diverse biological activities. Many endogenous peptides, especially neuropeptides and peptide hormones, play critical roles in development and regulating homeostasis. Furthermore, as drug candidates their high receptor selectivity and potent binding leads to reduced off-target interactions and potential negative side effects. However, the therapeutic potential of peptides is severely hampered by their poor stability in vivo and low permeability across biological membranes. Several strategies have been successfully employed over the decades to address these concerns, and one of the most promising strategies is glycosylation. It has been demonstrated in numerous cases that glycosylation is an effective synthetic approach to improve the pharmacokinetic profiles and membrane permeability of peptides. The effects of glycosylation on peptide stability and peptide-membrane interactions in the context of blood-brain barrier penetration will be explored. Numerous examples of glycosylated analogues of endogenous peptides targeting class A and B G-protein coupled receptors (GPCRs) with an emphasis on O-linked glycopeptides will be reviewed. Notable examples of N-, S-, and C-linked glycopeptides will also be discussed. A small section is devoted to synthetic methods for the preparation of glycopeptides and requisite amino acid glycoside building blocks.

Transcriptomic profiling revealed key signaling pathways for cold tolerance and acclimation of two carp species

Background

Closely related species of the carp family (Cyprinidae) have evolved distinctive abilities to survive under cold stress, but molecular mechanisms underlying the generation of cold resistance remain largely unknown. In this study, we compared transcriptomic profiles of two carp species to identify key factors and pathways for cold tolerance and acclimation.

Results

Larvae of Songpu mirror carp and Barbless carp that were pretreated at 18 °C for 24 h significantly improved their survival rates under lethal cold temperature at 8 °C or 10 °C, indicating that two carp species possess the ability of cold acclimation. However, Songpu mirror carp exhibited stronger abilities of cold tolerance and acclimation than Barbless carp. Transcriptomic profiles of Songpu mirror carp and Barbless carp larvae at 28 °C and 18 °C were compared during cold acclimation through RNA-seq. Differentially expressed genes that are closely associated with the differences in cold acclimation between two carp species were identified through bioinformatics and Venn’s diagram analysis. GO enrichment analysis of these genes indicated that cellular component assembly involved in morphogenesis, secondary alcohol metabolism and drug transport were the most up-regulated biological processes during cold acclimation of Songpu mirror carp. Conversely, positive regulation of macroautophagy, intracellular protein transport, and organonitrogen compound catabolism were the most down-regulated biological processes during cold acclimation of Barbless carp. KEGG enrichment analysis revealed that factors in the FoxO-related signaling pathways are mainly responsible for the development of differences in cold tolerance and acclimation between two carp species since altering the phosphorylation of key proteins in the FoxO-related signaling pathways with inhibitors or an activator significantly decreased the cold tolerance and acclimation of Songpu mirror carp. These data provided key clues for dissection of molecular mechanisms underlying the development of cold tolerance and acclimation in carps.

Conclusions

These findings indicate that larvae of two carp species possess different abilities of cold tolerance and can build cold acclimation under mild low temperature. Multiple biological processes and FoxO-related signaling pathways are closely associated with the development of differences in cold tolerance and acclimation between two carp species.

X-ray diffraction to probe the kinetics of ice recrystallization inhibition

Understanding the nucleation and growth of ice is crucial in fields ranging from infrastructure maintenance, to the environment, and to preserving biologics in the cold chain. Ice binding and antifreeze proteins are potent ice recrystallization inhibitors (IRI), and synthetic materials that mimic this function have emerged, which may find use in biotechnology. To evaluate IRI activity, optical microscopy tools are typically used to monitor ice grain size either by end-point measurements or as a function of time. However, these methods provide 2-dimensional information and image analysis is required to extract the data. Here we explore using wide angle X-ray scattering (WAXS/X-ray powder diffraction (XRD)) to interrogate 100's of ice crystals in 3-dimensions as a function of time. Due to the random organization of the ice crystals in the frozen sample, the number of orientations measured by XRD is proportional to the number of ice crystals, which can be measured as a function of time. This method was used to evaluate the activity for a panel of known IRI active compounds, and shows strong agreement with results obtained from cryo-microscopy, as well as being advantageous in that time-dependent ice growth is easily extracted. Diffraction analysis also confirmed, by comparing the obtained diffraction patterns of both ice binding and non-binding additives, that the observed hexagonal ice diffraction patterns obtained cannot be used to determine which crystal faces are being bound. This method may help in the discovery of new IRI active materials as well as enabling kinetic analysis of ice growth.

Computational Study of Differences between Antifreeze Activity of Type-III Antifreeze Protein from Ocean Pout and Its Mutant

The antifreeze activity of a type-III antifreeze protein (AFP) expressed in ocean pout (Zoarces americanus) is compared with that of a specific mutant (T18N) using all-atom molecular dynamics simulations. The antifreeze activity of the mutant is only 10% of the wild-type AFP. The results from this simulation study revealed the following insights into the mechanism of antifreeze action by type-III AFPs. The AFP gets adsorbed to the advancing ice front due to its hydrophobic nature. A part of the hydrophobicity is caused by the presence of clathrate structure of water molecules near the ice-binding surface (IBS). The mutation in the AFP disrupts this structure and thereby reduces the ability of the mutant to adsorb to the ice-water interface leading to the loss of antifreeze activity. The mutation, however, has no effect on the ability of the adsorbed protein to bind to the growing ice phase. Simulations also revealed that all surfaces of the protein can bind to the ice phase, although the IBS is the preferred surface.

Fish-Derived Antifreeze Proteins and Antifreeze Glycoprotein Exhibit a Different Ice-Binding Property with Increasing Concentration

The concentration of a protein is highly related to its biochemical properties, and is a key determinant for its biotechnological applications. Antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs) are structurally diverse macromolecules that are capable of binding to embryonic ice crystals below 0 °C, making them useful as protectants of ice-block formation. In this study, we examined the maximal solubility of native AFP I–III and AFGP with distilled water, and evaluated concentration dependence of their ice-binding property. Approximately 400 mg/mL (AFP I), 200 mg/mL (AFP II), 100 mg/mL (AFP III), and >1800 mg/mL (AFGP) of the maximal solubility were estimated, and among them AFGP’s solubility is much higher compared with that of ordinary proteins, such as serum albumin (~500 mg/mL). The samples also exhibited unexpectedly high thermal hysteresis values (2–3 °C) at 50–200 mg/mL. Furthermore, the analysis of fluorescence-based ice plane affinity showed that AFP II binds to multiple ice planes in a concentration-dependent manner, for which an oligomerization mechanism was hypothesized. The difference of concentration dependence between AFPs and AFGPs may provide a new clue to help us understand the ice-binding function of these proteins.

Ice Binding Proteins: Diverse Biological Roles and Applications in Different Types of Industry

More than 80% of Earth’s surface is exposed periodically or continuously to temperatures below 5 °C. Organisms that can live in these areas are called psychrophilic or psychrotolerant. They have evolved many adaptations that allow them to survive low temperatures. One of the most interesting modifications is production of specific substances that prevent living organisms from freezing. Psychrophiles can synthesize special peptides and proteins that modulate the growth of ice crystals and are generally called ice binding proteins (IBPs). Among them, antifreeze proteins (AFPs) inhibit the formation of large ice grains inside the cells that may damage cellular organelles or cause cell death. AFPs, with their unique properties of thermal hysteresis (TH) and ice recrystallization inhibition (IRI), have become one of the promising tools in industrial applications like cryobiology, food storage, and others. Attention of the industry was also caught by another group of IBPs exhibiting a different activity—ice-nucleating proteins (INPs). This review summarizes the current state of art and possible utilizations of the large group of IBPs.

Polyampholytes as Emerging Macromolecular Cryoprotectants

Cellular cryopreservation is a platform technology which underpins cell biology, biochemistry, biomaterials, diagnostics, and the cold chain for emerging cell-based therapies. This technique relies on effective methods for banking and shipping to avoid the need for continuous cell culture. The most common method to achieve cryopreservation is to use large volumes of organic solvent cryoprotective agents which can promote either a vitreous (ice free) phase or dehydrate and protect the cells. These methods are very successful but are not perfect: not all cell types can be cryopreserved and recovered, and the cells do not always retain their phenotype and function post-thaw. This Perspective will introduce polyampholytes as emerging macromolecular cryoprotective agents and demonstrate they have the potential to impact a range of fields from cell-based therapies to basic cell biology and may be able to improve, or replace, current solvent-based cryoprotective agents. Polyampholytes have been shown to be remarkable (mammalian cell) cryopreservation enhancers, but their mechanism of action is unclear, which may include membrane protection, solvent replacement, or a yet unknown protective mechanism, but it seems the modulation of ice growth (recrystallization) may only play a minor role in their function, unlike other macromolecular cryoprotectants. This Perspective will discuss their synthesis and summarize the state-of-the-art, including hypotheses of how they function, to introduce this exciting area of biomacromolecular science.

Synthesis of Anthracene Conjugates of Truncated Antifreeze Protein Sequences: Effect of the End Group and Photocontrolled Dimerization on Ice Recrystallization Inhibition Activity

Biomacromolecular antifreezes distinguish ice from water, function by binding to specific planes of ice, and could have many applications from cryobiology to aerospace where ice is a problem. In biology, antifreeze protein (AFP) activity is regulated by protein expression levels via temperature and light-regulated expression systems, but in the laboratory (or applications), the antifreeze activity is "always on" without any spatial or temporal control, and hence methods to enable this switching represent an exciting synthetic challenge. Introduction of an abiotic functionality into short peptides (e.g., from solid-phase synthesis) to enable switching is also desirable rather than on full-length recombinant proteins. Here, truncated peptide sequences based on the consensus repeat sequence from type-I AFPs (TAANAAAAAAA) were conjugated to an anthracene unit to explore their photocontrolled dimerization. Optimization of the synthesis to ensure solubility of the hydrophobic peptide included the addition of a dilysine solubilizing linker. It was shown that UV-light exposure triggered reversible dimerization of the AFP sequence, leading to an increase in molecular weight. Assessment of the ice recrystallization inhibition activity of the peptides before and after dimerization revealed only small effects on activity. However, it is reported here for the first time that addition of the anthracene unit to a 22-amino-acid truncated peptide significantly enhanced ice recrystallization inhibition compared to the free peptide, suggesting an accessible synthetic route to allow AFP activity using shorter, synthetically accessible peptides with a photoreactive functionality.

Peptidic Antifreeze Materials: Prospects and Challenges

Necessitated by the subzero temperatures and seasonal exposure to ice, various organisms have developed a remarkably effective means to survive the harsh climate of their natural habitats. Their ice-binding (glyco)proteins keep the nucleation and growth of ice crystals in check by recognizing and binding to specific ice crystal faces, which arrests further ice growth and inhibits ice recrystallization (IRI). Inspired by the success of this adaptive strategy, various approaches have been proposed over the past decades to engineer materials that harness these cryoprotective features. In this review we discuss the prospects and challenges associated with these advances focusing in particular on peptidic antifreeze materials both identical and akin to natural ice-binding proteins (IBPs). We address the latest advances in their design, synthesis, characterization and application in preservation of biologics and foods. Particular attention is devoted to insights in structure-activity relations culminating in the synthesis of de novo peptide analogues. These are sequences that resemble but are not identical to naturally occurring IBPs. We also draw attention to impactful developments in solid-phase peptide synthesis and 'greener' synthesis routes, which may aid to overcome one of the major bottlenecks in the translation of this technology: unavailability of large quantities of low-cost antifreeze materials with excellent IRI activity at (sub)micromolar concentrations.

Bioinspired Ice Growth Inhibitors Based on Self-Assembling Peptides

Antifreeze proteins (AFPs) are widely found in organisms living in subzero environments. Their strong ability to inhibit ice growth and recrystallization have inspired considerable bioinspired efforts to engineer artificial ice growth inhibitors for cryopreservation. However, it remains challenging to engineer biocompatible and cost-effective synthetic ice growth inhibitors to meet the increasing needs of cryoprotectants in biomedical research and industry. Here we report the design of artificial ice growth inhibitors based on self-assembling peptides. We demonstrate the importance of threonine residues as well as their spatial arrangement for effective ice binding. The engineered self-assembling ice growth inhibiting peptides show moderate ice inhibiting activity including suppression of ice growth rates and retardation of recrystallization of ice crystals. The applications of these peptides in cryopreservation of enzymes and cells were also demonstrated.

Mimicking the Ice Recrystallization Activity of Biological Antifreezes. When is a New Polymer "Active"?

Antifreeze proteins and ice-binding proteins have been discovered in a diverse range of extremophiles and have the ability to modulate the growth and formation of ice crystals. Considering the importance of cryoscience across transport, biomedicine, and climate science, there is significant interest in developing synthetic macromolecular mimics of antifreeze proteins, in particular to reproduce their property of ice recrystallization inhibition (IRI). This activity is a continuum rather than an "on/off" property and there may be multiple molecular mechanisms which give rise to differences in this observable property; the limiting concentrations for ice growth vary by more than a thousand between an antifreeze glycoprotein and poly(vinyl alcohol), for example. The aim of this article is to provide a concise comparison of a range of natural and synthetic materials that are known to have IRI, thus providing a guide to see if a new synthetic mimic is active or not, including emerging materials which are comparatively weak compared to antifreeze proteins, but may have technological importance. The link between activity and the mechanisms involving either ice binding or amphiphilicity is discussed and known materials assigned into classes based on this.

Site-specific conjugation of antifreeze proteins onto polymer-stabilized nanoparticles

Antifreeze proteins (AFPs) have many potential applications, ranging from cryobiology to aerospace, if they can be incorporated into materials. Here, a range of engineered AFP mutants were prepared and site-specifically conjugated onto RAFT polymer-stabilized gold nanoparticles to generate new hybrid multivalent ice growth inhibitors. Only the SNAP-tagged AFPs lead to potent 'antifreeze' active nanomaterials with His-Tag capture resulting in no activity, showing the mode of conjugation is essential. This versatile strategy will enable the development of multivalent AFPs for translational and fundamental studies.

The Ensemble of Conformations of Antifreeze Glycoproteins (AFGP8): A Study Using Nuclear Magnetic Resonance Spectroscopy

The primary sequence of antifreeze glycoproteins (AFGPs) is highly degenerate, consisting of multiple repeats of the same tripeptide, Ala–Ala–Thr*, in which Thr* is a glycosylated threonine with the disaccharide beta-d-galactosyl-(1,3)-alpha-N-acetyl-d-galactosamine. AFGPs seem to function as intrinsically disordered proteins, presenting challenges in determining their native structure. In this work, a different approach was used to elucidate the three-dimensional structure of AFGP8 from the Arctic cod Boreogadussaida and the Antarctic notothenioid Trematomusborchgrevinki. Dimethyl sulfoxide (DMSO), a non-native solvent, was used to make AFGP8 less dynamic in solution. Interestingly, DMSO induced a non-native structure, which could be determined via nuclear magnetic resonance (NMR) spectroscopy. The overall three-dimensional structures of the two AFGP8s from two different natural sources were different from a random coil ensemble, but their “compactness” was very similar, as deduced from NMR measurements. In addition to their similar compactness, the conserved motifs, Ala–Thr*–Pro–Ala and Ala–Thr*–Ala–Ala, present in both AFGP8s, seemed to have very similar three-dimensional structures, leading to a refined definition of local structural motifs. These local structural motifs allowed AFGPs to be considered functioning as effectors, making a transition from disordered to ordered upon binding to the ice surface. In addition, AFGPs could act as dynamic linkers, whereby a short segment folds into a structural motif, while the rest of the AFGPs could still be disordered, thus simultaneously interacting with bulk water molecules and the ice surface, preventing ice crystal growth.

Multivalent Presentation of Ice Recrystallization Inhibiting Polymers on Nanoparticles Retains Activity

Poly(vinyl alcohol) (PVA) has emerged as the most potent mimic of antifreeze (glyco)proteins ice recrystallization inhibition (IRI) activity, despite its lack of structural similarities and flexible, rather than rigid, backbone. The precise spacing of hydroxyl groups is hypothesized to enable PVA to recognize the prism planes of ice but not the basal plane, due to hydroxyl pattern matching of the ice surface giving rise to the macroscopic activity. Here, well-defined PVA derived from reversible addition-fragmentation chain-transfer (RAFT) polymerization is immobilized onto gold nanoparticles to enable the impact of nanoscale assembly and confinement on the observed IRI activity. Unlike previous reports using star-branched or bottle-brush PVAs, the nanoparticle-PVA retains all IRI activity compared to polymers in solution. Evidence is presented to show that this is due to the low grafting densities on the particle surface meaning the chains are free to explore the ice faces, rather than being constrained as in star-branched polymers. These results demonstrate a route to develop more functional IRI's and inclusion of metallic particle cores for imaging and associated applications in cryobiology.

The Use of Antifreeze Proteins in the Cryopreservation of Gametes and Embryos

The cryopreservation of gametes and embryos is a technique widely used in reproductive biology. This technology helps in the reproductive management of domesticated animals, and it is an important tool for gene banking and for human-assisted reproductive technologies. Antifreeze proteins are naturally present in several organisms exposed to subzero temperatures. The ability for these proteins to inhibit ice recrystallization together with their ability to interact with biological membranes makes them interesting molecules to be used in cryopreservation protocols. This mini-review provides a general overview about the use of antifreeze proteins to improve the short and long term storage of gametes and embryos.

Cluster binding studies with two anti-Thomsen-Friedenreich (anti-core-1, CD176, TF) antibodies: Evidence for a multiple TF epitope

Antibodies to carbohydrate epitopes are often of the IgM isotype and require multiple binding for sufficient avidity. Therefore clusters of epitopes are preferred antigenic sites in these cases. We have examined the type of clusters recognized by two anti-Thomsen-Friedenreich (TF, core-1, CD176) IgM antibodies, NM-TF1 and NM-TF2, using several different sets of TF-carrying synthetic glycoconjugates in ELISA experiments. To our surprise, the single most important factor determining binding strength was a close vicinity of several TF glycans at distances of ≤1 nm. Considering the known dimensions of IgM antibodies, our data strongly suggest that a cluster of up to four TF moieties, presenting as a "multiple epitope", is required to attach to a single combining site in order to result in adequate binding strength. This effect can also be achieved by "surrogate-multiple epitopes" consisting of separate TF-carrying molecules in close vicinity. In addition, it was found that serine-linked TFs are stronger bound than threonine-linked TFs by both antibodies. This peculiar type of cluster recognition may contribute to improved avidity and explicit tumor specificity.

Ice-recrystallization inhibiting polymers protect proteins against freeze-stress and enable glycerol-free cryostorage

Proteins are ubiquitous in molecular biotechnology, biotechnology and as therapeutics, but there are significant challenges in their storage and distribution, with freezing often required. This is traditionally achieved by the addition of cryoprotective agents such as glycerol (or trehalose) or covalent modification of mutated proteins with cryoprotectants. Here, ice recrystallization inhibiting polymers, inspired by antifreeze proteins, are used synergistically with poly(ethylene glycol) as an alternative to glycerol. The primary mechanism of action appears to be preventing irreversible aggregation due to ice growth. The polymer formulation is successfully used to cryopreserve a range of important proteins including insulin, Taq DNA polymerase and an IgG antibody. The polymers do not require covalent conjugation, nor modification of the protein and are already used in a wide range of biomedical applications, which will facilitate translation to a range of biologics.

Synthesis of the tetrasaccharide repeating unit of the cryoprotectant capsular polysaccharide from Colwellia psychrerythraea 34H

Synthesis of the threonine-decorated tetrasaccharide repeating unit of a cryoprotectant polysaccharide with a glycosaminoglycan-like structure.

Sub-zero temperature mechanically stable low molecular weight hydrogels

We show here a low molecular weight hydrogelator based on a functionalised-dipeptide which is stable down to temperatures of -12 °C despite being made from >99% water. This stabilty at low temperature can be extended to ∼-40 °C by gelling water : glycerol mixtures. The temperature range is wider than that of the glycerol : water mixtures alone. The rheological properties of the gels do not change at this low temperature compared to that of gels at 25 °C. This freezing point depression offers a potentially new method of transporting gels and offers the prospect of hydrogels being used at much lower working temperatures whilst retaining the desired rheological properties, this is useful for cryopreservation.

Novel technologies in utilization of byproducts of animal food processing: a review

China is one of the countries with most abundant livestock and poultry resources in the world. The average annual growth rate of output value of livestock and poultry industry reaches 13%, and the output value of livestock and poultry industry accounts for more than 35% of total agricultural output. A large number of byproducts are produced in animal slaughtering and processing operations. If livestock and poultry byproducts are effectively utilized, this will make a huge contribution to GDP. At the same time, aquaculture is China's pillar industry. During fish processing, a large number of byproducts (including fish heads, fish skins, fish bones, fish scales, and viscera) are produced, which weighs approximately 40-55% of the raw fish. The byproducts of freshwater fish are more than 2.5 million tons per annum, most of which are not used. The effective use of byproducts has a direct influence on China's economic and environmental pollution. The nonuse or underutilization of byproducts not only leads to loss of potential revenue, but also results in to an increase in these products and their disposal costs. This paper makes a comprehensive review of the research progress of animal byproduct utilization to date, and aims to provide reference for the utilization and research of animal byproducts.