Protein inclusion into ice can dissociate subunits.

An antifreeze protein's inclusion into ice can be used to purify it from other proteins and solutes. Domains that are covalently attached to the antifreeze protein are also drawn into the ice such that the ice-binding portion of the fusion protein can be used as an affinity tag. Here we have explored the use of ice-affinity tags on multi-subunit proteins. When an ice-binding protein was attached as a tag to multisubunit complexes a substantial portion of each multimer dissociated during overgrowth by the ice. The protein subunit attached to the affinity tag was enriched in the ice and the other subunit was appreciably excluded. We suggest that step growth of the advancing ice front generates shearing forces on the bound complex that can disrupt non-covalent protein-protein interactions. This will effectively limit the use of ice-affinity tags to single subunit proteins.

Isolation and Characterization of Ice-Binding Proteins from Higher Plants.

The characterization of ice-binding proteins (IBPs) from plants can involve many techniques, a few of which are presented here. Chief among these methods are tests for ice recrystallization inhibition, an activity characteristic of plant IBPs. Two related procedures are described, both of which can be used to demonstrate and quantify ice-binding activity. First, is the traditional "splat" assay, which can easily be set up using common laboratory equipment, and second, is our modification of this method using superhydrophobic coated sapphire for analysis of multiple samples in tandem. Thermal hysteresis is described as another method for quantifying ice-binding activity, during which ice crystal morphology observations can be used to provide clues about ice-plane binding. Once ice-binding activity has been evaluated, it is necessary to verify IBP identity. We detail two methods for enriching IBPs from complex mixtures using ice-affinity purification, the "ice-finger" and "ice-shell" methods, and we highlight their advantages and limitations for the isolation of plant IBPs. Recombinant IBP expression, necessary for detailed ice-binding analysis, can present challenges. Here, a strategy for recovery of soluble, active protein is described. Lastly, verification of function in planta borrows from standard protocols, but with an additional screen applicable to IBPs. Together, these methods, and a few considerations critical to success, can be used to assist researchers wishing to isolate and characterize IBPs from plants.

Performance of antifreeze protein HrCHI4 from Hippophae rhamnoides in improving the structure and freshness of green beans upon cryopreservation.

Antifreeze proteins restrict the growth of ice crystals during recrystallization and therefore find application in the protection of food products from damage upon freezing. Hippophae rhamnoides (seabuckthorn) is a freeze tolerant Himalayan shrub exhibiting antifreeze properties. Here, ~39 kDa class IV chitinase (HrCHI4) was purified from seabuckthorn seeds using chitin-affinity chromatography that showed antifreeze property by ice recrystallization inhibition. The application of HrCHI4 in cryopreservation of green beans was analyzed to verify its antifreeze potential. HrCHI4 pretreatment reduced the drip loss and electrolytic leakage in frozen beans, revealing that it preserved the membrane integrity upon cryopreservation. The texture analysis and SEM further validated structural maintenance. The volatile component analysis using GC-MS was performed to evaluate the quality of frozen beans. HrCHI4 contributed positively towards the retention of volatile components after freeze-thaw. In conclusion, a class IV chitinase HrCHI4 was purified from seabuckthorn seeds and its cryoprotective function was reported.

Laboratory-Scale Isolation of Insect Antifreeze Protein for Cryobiology.

Micromolar concentrations of hyperactive antifreeze proteins (AFPs) from insects can prevent aqueous solutions from freezing down to at least -6 °C. To explore cryopreservation of cells, tissues and organs at these temperatures without ice formation, we have developed a protocol to reliably produce ultrapure Tenebrio molitor AFP from cold-acclimated beetle larvae reared in the laboratory. The AFP was prepared from crude larval homogenates through five cycles of rotary ice-affinity purification, which can be completed in one day. Recovery of the AFP at each step was >90% and no impurities were detected in the final product. The AFP is a mixture of isoforms that are more active in combination than any one single component. Toxicity testing of the purified AFP in cell culture showed no inhibition of cell growth. The production process can easily be scaled up to industrial levels, and the AFP used in cryobiology applications was recovered for reuse in good yield and with full activity.

Extraction of antifreeze proteins from cold acclimated leaves of Drimys angustifolia and their application to star fruit (Averrhoa carambola) freezing.

Antifreeze proteins (AFPs) have the ability to modify ice crystal growth and thus there is great interest in identifying new sources of these compounds. All extracts of cold acclimated leaves of Drimys angustifolia, obtained using different buffers, inhibited recrystallization and they presented similar SDS-PAGE profiles, with bands close to 20 and 37 kDa. The extract obtained using Tris-HCl/DDT buffer (pH 8) was used in the pre-treatment of frozen star fruit (Averrhoa carambola) by immersion or vacuum infiltration. The treatments did not affect the titratable acidity, pH, soluble solids, ascorbic acid content and colour. However, only star fruits that were vacuum infiltrated with AFPs retained their drip loss constant after 15 days. Moreover, with this treatment the star fruit firmness was maintained on thawing after 60 days of storage. The vacuum infiltration of Drimys angustifolia AFPs into the star fruit allowed an initial cryoprotection, indicating that the application of AFPs can increase the quality of frozen star fruit.

Effect of Antifreeze Glycoproteins on Organoid Survival during and after Hypothermic Storage.

We study the effect of antifreeze glycoproteins (AFGPs) on the survival of organoids under hypothermic conditions. We find that the survival of organoids in cold conditions depends on their developmental stage. Mature organoids die within 24 h when being stored at 4 °C, while cystic organoids can survive up to 48 h. We find that in the presence of AFGPs, the organoid survival is prolonged up to 72 h, irrespective of their developmental stage. Fluorescence microscopy experiments reveal that the AFGPs predominately localize at the cell surface and cover the cell membranes. Our findings support a mechanism in which the positive effect of AFGPs on cell survival during hypothermic storage involves the direct interaction of AFGPs with the cell membrane. Our research highlights organoids as an attractive multicellular model system for studying the action of AFGPs that bridges the gap between single-cell and whole-organ studies.

Applications of Antifreeze Proteins: Practical Use of the Quality Products from Japanese Fishes.

Numerous embryonic ice crystals are generated in water at the moment of freezing. These crystals grow and merge together to form an ice block that can be generally observed. Antifreeze protein (AFP) is capable of binding to the embryonic ice crystals, inhibiting such an ice block formation. Fish-derived AFP additionally binds to membrane lipid bilayers to prolong the lifetime of cells. These unique abilities of AFP have been studied extensively for the development of advanced techniques, such as ice recrystallization inhibitors, freeze-tolerant gels, cell preservation fluids, and high-porosity ceramics, for which mass-preparation method of the quality product of AFP utilizing fish muscle homogenates made a significant contribution. In this chapter, we present both fundamental and advanced information of fish AFPs that have been especially discovered from mid-latitude sea area, which will provide a hint to develop more advanced techniques applicable in both medical and industrial fields.

Single-step purification and characterization of antifreeze proteins from leaf and berry of a freeze-tolerant shrub seabuckthorn (Hippophae rhamnoides).

Seabuckthorn is a freeze-tolerant Himalayan shrub, capable of withstanding temperatures below -40°C. Antifreeze proteins prevent freezing associated damage by restricting ice crystals growth. In the present study, homogenous purification of two antifreeze proteins (41 and 39 kDa) from Hippophae rhamnoides leaf and one (41 kDa) from berry was performed using ice-affinity chromatography. MS identification and Basic Local Alignment Search Tool search showed homology of berry antifreeze proteins with disease resistance protein while leaf antifreeze proteins showed similarity with transmembrane protein (39 kDa) and low temperature induced protein (41 kDa) suggesting their role in cold stress signalling. Hexagon shaped ice crystals (Nanoliter osmometer) and ice recrystallization inhibition assay (Splat assay) confirmed higher ice recrystallization inhibition activity of purified leaf (2.5 fold decrease in mean ice crystal size) and berry (2.1 fold decrease) antifreeze proteins. String interactome analysis showed interaction of antifreeze proteins with cold stress modulated targets including pathogenesis related proteins. This probably is the first report of antifreeze proteins purification from naturally growing seabuckthorn. Further validation of these targets may open gates for commercial utilization of this plant growing abundantly in Himalayan regions of India, for crop improvement of freeze susceptible crops or biomedical applications like cryopreservation of tissues and cells.

Structural characterization of an all-aminosugar-containing capsular polysaccharide from Colwellia psychrerythraea 34H.

Colwellia psychrerythraea strain 34H, a Gram-negative bacterium isolated from Arctic marine sediments, is considered a model to study the adaptation to cold environments. Recently, we demonstrated that C. psychrerythraea 34H produces two different extracellular polysaccharides, a capsular polysaccharide and a medium released polysaccharide, which confer cryoprotection to the bacterium. In this study, we report the structure of an additional capsular polysaccharide produced by Colwellia grown at a different temperature. The structure was determined using chemical methods, and one- and two-dimensional NMR spectroscopy. The results showed a trisaccharide repeating unit made up of only amino-sugar residues: N-acetyl-galactosamine, 2,4-diacetamido-2,4,6-trideoxy-glucose (bacillosamine), and 2-acetamido-2-deoxyglucuronic acid with the following structure: â†’4)-ß-D-GlcpNAcA-(1 â†’3)-ß-D-QuipNAc4NAc-(1 â†’3)-ß-D-GalpNAc-(1 â†’. The 3D model, generated in accordance with 1H,1H-NOE NMR correlations and consisting of ten repeating units, shows a helical structure. In contrast with the other extracellular polysaccharides produced from Colwellia at 4 °C, this molecule displays only a low ice recrystallization inhibition activity.

Ice-shell purification of ice-binding proteins.

Ice-affinity purification is a simple and efficient method of purifying to homogeneity both natural and recombinant ice-binding proteins. The purification involves the incorporation of ice-binding proteins into slowly-growing ice and the exclusion of other proteins and solutes. In previous approaches, the ice was grown around a hollow brass finger through which coolant was circulated. We describe here an easily-constructed apparatus that employs ice affinity purification that not only shortens the time for purification from 1-2 days to 1-2 h, but also enhances yield and purity. In this apparatus, the surface area for the separation was increased by extracting the ice-binding proteins into an ice-shell formed inside a rotating round-bottom flask partially submerged in a sub-zero bath. In principle, any ice-binding compound can be recovered from liquid solution, and the method is readily scalable.

Inhibition of ice recrystallization and cryoprotective activity of wheat proteins in liver and pancreatic cells.

Efficient cryopreservation of cells at ultralow temperatures requires the use of substances that help maintain viability and metabolic functions post-thaw. We are developing new technology where plant proteins are used to substitute the commonly-used, but relatively toxic chemical dimethyl sulfoxide. Recombinant forms of four structurally diverse wheat proteins, TaIRI-2 (ice recrystallization inhibition), TaBAS1 (2-Cys peroxiredoxin), WCS120 (dehydrin), and TaENO (enolase) can efficiently cryopreserve hepatocytes and insulin-secreting INS832/13 cells. This study shows that TaIRI-2 and TaENO are internalized during the freeze-thaw process, while TaBAS1 and WCS120 remain at the extracellular level. Possible antifreeze activity of the four proteins was assessed. The "splat cooling" method for quantifying ice recrystallization inhibition activity (a property that characterizes antifreeze proteins) revealed that TaIRI-2 and TaENO are more potent than TaBAS1 and WCS120. Because of their ability to inhibit ice recrystallization, the wheat recombinant proteins TaIRI-2 and TaENO are promising candidates and could prove useful to improve cryopreservation protocols for hepatocytes and insulin-secreting cells, and possibly other cell types. TaENO does not have typical ice-binding domains, and the TargetFreeze tool did not predict an antifreeze capacity, suggesting the existence of nontypical antifreeze domains. The fact that TaBAS1 is an efficient cryoprotectant but does not show antifreeze activity indicates a different mechanism of action. The cryoprotective properties conferred by WCS120 depend on biochemical properties that remain to be determined. Overall, our results show that the proteins' efficiencies vary between cell types, and confirm that a combination of different protection mechanisms is needed to successfully cryopreserve mammalian cells.

Extraction, purification and identification of antifreeze proteins from cold acclimated malting barley (Hordeum vulgare L.).

Antifreeze proteins from cold-acclimated malting barley were extracted by infiltration-centrifugation. The infiltration time was optimised, and its extraction effect was evaluated. The effect of cold acclimation on the accumulation of barley antifreeze proteins (BaAFPs) was assessed by comparing the thermal hysteresis activities (THA) of proteins extracted from both cold acclimated and non-cold acclimated barley grain. Ultra-filtration, ammonium precipitation and column chromatography were used successively to purify the BaAFPs, and MALDI-TOF-MS/MS was used for protein identification. The results showed that infiltration-centrifugation was more targeted than the traditional method, and 10h was the optimal infiltration time. THA was observed only after cold acclimation implied that AFPs only began to accumulate after cold acclimation. After purification, BaAFP-I was obtained at an electrophoresis level and its THA was 1.04°C (18.0 mg ml(-1)). The mass fingerprinting and sequencing results indicated the homology of the BaAFP-I to alpha-amylase inhibitor BDAI-1 (Hordeum vulgare).

A unique capsular polysaccharide structure from the psychrophilic marine bacterium Colwellia psychrerythraea 34H that mimics antifreeze (glyco)proteins.

The low temperatures of polar regions and high-altitude environments, especially icy habitats, present challenges for many microorganisms. Their ability to live under subfreezing conditions implies the production of compounds conferring cryotolerance. Colwellia psychrerythraea 34H, a γ-proteobacterium isolated from subzero Arctic marine sediments, provides a model for the study of life in cold environments. We report here the identification and detailed molecular primary and secondary structures of capsular polysaccharide from C. psychrerythraea 34H cells. The polymer was isolated in the water layer when cells were extracted by phenol/water and characterized by one- and two-dimensional NMR spectroscopy together with chemical analysis. Molecular mechanics and dynamics calculations were also performed. The polysaccharide consists of a tetrasaccharidic repeating unit containing two amino sugars and two uronic acids bearing threonine as substituent. The structural features of this unique polysaccharide resemble those present in antifreeze proteins and glycoproteins. These results suggest a possible correlation between the capsule structure and the ability of C. psychrerythraea to colonize subfreezing marine environments.

A 9 kDa antifreeze protein from the Antarctic springtail, Gomphiocephalus hodgsoni.

A 9 kDA antifreeze protein (AFP) was isolated and purified from the Antarctic springtail, Gomphiocephalus hodgsoni. By combining selective sampling procedures and a modified ice affinity purification protocol it was possible to directly isolate a single AFP protein without recourse to chromatographic separation techniques. Mass spectrometry identified a single 9 kDa component in the purified ice fraction. Intramolecular disulphide bonding was suggested by the presence of 12 cysteine residues. The specific amino acid composition is unique, particularly with regard to the presence of histidine (11.5%). But it also shows noticeable commonalities with insect AFPs in the abundance of cysteine (13.8%), while simultaneously hinting, through the presence of glycine (11.5%), that the metabolic building blocks of AFPs in Collembola may have a phylogenetically-determined component.

Isolation and characterization of ice-binding proteins from higher plants.

The characterization of ice-binding proteins from plants can involve many techniques, only a few of which are presented here. Chief among these methods are tests for ice recrystallization inhibition activity. Two distinct procedures are described; neither is normally used for precise quantitative assays. Thermal hysteresis assays are used for quantitative studies but are also useful for ice crystal morphologies, which are important for the understanding of ice-plane binding. Once the sequence of interest is cloned, recombinant expression, necessary to verify ice-binding protein identity can present challenges, and a strategy for recovery of soluble, active protein is described. Lastly, verification of function in planta borrows from standard protocols, but with an additional screen applicable to ice-binding proteins. Here we have attempted to assist researchers wishing to isolate and characterize ice-binding proteins from plants with a few methods critical to success.

Annealing condition influences thermal hysteresis of fungal type ice-binding proteins.

The Antarctic sea ice diatom Navicular glaciei produced ice-binding protein (NagIBP) that is similar to the antifreeze protein (TisAFP) from snow mold Typhula ishikariensis. In the thermal hysteresis range of NagIBP, ice growth was completely inhibited. At the freezing point, the ice grew in a burst to 6 direction perdicular to the c-axis of ice crystal. This burst pattern is similar to TisAFP and other hyperactive AFPs. The thermal hysteresis of NagIBP and TisAFP could be increased by decreasing a cooling rate to allow more time for the proteins to bind ice. This suggests the possible second binding of proteins occurs on the ice surface, which might increase the hysteresises to a sufficient level to prevent freezing of the brine pockets which habitat of N. glaciei. The secondary ice binding was described as that after AFP molecules bind onto the flat ice plane irreversibly, which was based on adsorption-inhibition mechanism model at the ice-water interface, convex ice front was formed and overgrew during normal TH measurement (no annealing) until uncontrolled growth at the nonequilibrium freezing point. The results suggested that NagIBP is a hyperactive AFP that is expressed for freezing avoidance.

Antifreeze peptides and glycopeptides, and their derivatives: potential uses in biotechnology.

Antifreeze proteins (AFPs) and glycoproteins (AFGPs), collectively called AF(G)Ps, constitute a diverse class of proteins found in various Arctic and Antarctic fish, as well as in amphibians, plants, and insects. These compounds possess the ability to inhibit the formation of ice and are therefore essential to the survival of many marine teleost fishes that routinely encounter sub-zero temperatures. Owing to this property, AF(G)Ps have potential applications in many areas such as storage of cells or tissues at low temperature, ice slurries for refrigeration systems, and food storage. In contrast to AFGPs, which are composed of repeated tripeptide units (Ala-Ala-Thr)n with minor sequence variations, AFPs possess very different primary, secondary, and tertiary structures. The isolation and purification of AFGPs is laborious, costly, and often results in mixtures, making characterization difficult. Recent structural investigations into the mechanism by which linear and cyclic AFGPs inhibit ice crystallization have led to significant progress toward the synthesis and assessment of several synthetic mimics of AFGPs. This review article will summarize synthetic AFGP mimics as well as current challenges in designing compounds capable of mimicking AFGPs. It will also cover our recent efforts in exploring whether peptoid mimics can serve as structural and functional mimics of native AFGPs.

Cod glycopeptide with picomolar affinity to galectin-3 suppresses T-cell apoptosis and prostate cancer metastasis.

Cancer metastasis and immune suppression are critical issues in cancer therapy. Here, we show that a ß-galactoside-binding lectin [galectin-3 (gal3)] that recognizes the Thomsen-Friedenreich disaccharide (TFD, Galß1,3GalNAc) present on the surface of most cancer cells is involved in promoting angiogenesis, tumor-endothelial cell adhesion, and metastasis of prostate cancer cells, as well as evading immune surveillance through killing of activated T cells. To block gal3-mediated interactions, we purified a glycopeptide from cod (designated TFD100) that binds gal3 with picomolar affinity. TFD100 blocks gal3-mediated angiogenesis, tumor-endothelial cell interactions, and metastasis of prostate cancer cells in mice at nanomolar levels. Moreover, apoptosis of activated T cells induced by either recombinant gal3 or prostate cancer patient serum-associated gal3 was inhibited at nanomolar concentration of TFD100. Because the gal3-TFD interaction is a key factor driving metastasis in most epithelial cancers, this high-affinity TFD100 should be a promising antimetastatic agent for the treatment of various cancers, including prostate adenocarcinoma.

Characterization of Afp1, an antifreeze protein from the psychrophilic yeast Glaciozyma antarctica PI12.

The psychrophilic yeast Glaciozyma antarctica demonstrated high antifreeze activity in its culture filtrate. The culture filtrate exhibited both thermal hysteresis (TH) and ice recrystallization inhibition (RI) properties. The TH of 0.1 °C was comparable to that previously reported for bacteria and fungi. A genome sequence survey of the G. antarctica genome identified a novel antifreeze protein gene. The cDNA encoded a 177 amino acid protein with 30 % similarity to a fungal antifreeze protein from Typhula ishikariensis. The expression levels of AFP1 were quantified via real time-quantitative polymerase chain reaction (RT-qPCR), and the highest expression levels were detected within 6 h of growth at -12 °C. The cDNA of the antifreeze protein was cloned into an Escherichia coli expression system. Expression of recombinant Afp1 in E. coli resulted in the formation of inclusion bodies that were subsequently denatured by treatment with urea and allowed to refold in vitro. Activity assays of the recombinant Afp1 confirmed the antifreeze protein properties with a high TH value of 0.08 °C.

Hyperactive antifreeze proteins from longhorn beetles: some structural insights.

This study reports on structural characteristics of hyperactive antifreeze proteins (AFPs) from two species of longhorn beetles. In Rhagium mordax, eight unique mRNAs coding for five different mature AFPs were identified from cold-hardy individuals. These AFPs are apparently homologues to a previously characterized AFP from the closely related species Rhagium inquisitor, and consist of six identifiable repeats of a putative ice binding motif TxTxTxT spaced irregularly apart by segments varying in length from 13 to 20 residues. Circular dichroism spectra show that the AFPs from both species have a high content of ß-sheet and low levels of α-helix and random coil. Theoretical predictions of residue-specific secondary structure locate these ß-sheets within the putative ice-binding motifs and the central parts of the segments separating them, consistent with an overall ß-helical structure with the ice-binding motifs stacked in a ß-sheet on one side of the coil. Molecular dynamics models based on these findings show that these AFPs would be energetically stable in a ß-helical conformation.