The role of endogenous antifreeze protein enhancers in the hemolymph thermal hysteresis activity of the beetle Dendroides canadensis

Expeditious chemical synthesis of xylomannans disproves the proposed antifreeze activities

Cold-adapted species are able to generate cryoprotective proteins and glycoproteins to prevent freezing damage. The [→4)-β-D-Manp-(1→4)-β-D-Xylp-(1→] n xylomannan from the Alaska beetle Upis ceramboides was disclosed by Walters and co-workers in 2009 as the first glycan-based antifreeze agent, which was later reported to be found in diverse taxa. Here, we report the rapid synthesis of four types of xylomannans, including the proposed antifreeze xylomannan up to a 64-mer (Type I), the regioisomeric [→3)-β-D-Manp-(1→4)-β-D-Xylp-(1→] n 16-mer (Type II), the diastereomeric [→4)-β-L-Manp-(1→4)-β-D-Xylp-(1→] n 16-mer (Type III) and the block-wise [→4)-β-D-Manp-(1→] m [→4)-β-D-Xylp-(1→] n 32-mer (Type IV), by employing a strategic iterative exponential glycan growth (IEGG) process. The nuclear magnetic resonance spectral data of the alleged natural xylomannan are in accordance only to those of the block-wise Type IV glycan and none of these synthetic xylomannans has been found to be capable of inducing thermal hysteresis. These results disprove the previous reports about the natural occurrence of antifreeze xylomannans.

The Spruce Budworm Genome: Reconstructing the Evolutionary History of Antifreeze Proteins

Insects have developed various adaptations to survive harsh winter conditions. Among freeze-intolerant species, some produce "antifreeze proteins" (AFPs) that bind to nascent ice crystals and inhibit further ice growth. Such is the case of the spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae), a destructive North American conifer pest that can withstand temperatures below -30°C. Despite the potential importance of AFPs in the adaptive diversification of Choristoneura, genomic tools to explore their origins have until now been limited. Here we present a chromosome-scale genome assembly for C. fumiferana, which we used to conduct comparative genomic analyses aimed at reconstructing the evolutionary history of tortricid AFPs. The budworm genome features 16 genes homologous to previously reported C. fumiferana AFPs (CfAFPs), 15 of which map to a single region on chromosome 18. Fourteen of these were also detected in five congeneric species, indicating Choristoneura AFP diversification occurred before the speciation event that led to C. fumiferana. Although budworm AFPs were previously considered unique to the genus Choristoneura, a search for homologs targeting recently sequenced tortricid genomes identified seven CfAFP-like genes in the distantly related Notocelia uddmanniana. High structural similarity between Notocelia and Choristoneura AFPs suggests a common origin, despite the absence of homologs in three related tortricids. Interestingly, one Notocelia AFP formed the C-terminus of a "zonadhesin-like" protein, possibly representing the ancestral condition from which tortricid AFPs evolved. Future work should clarify the evolutionary path of AFPs between Notocelia and Choristoneura and assess the role of the "zonadhesin-like" protein as precursor of tortricid AFPs.

Bioinspired Ice-Binding Materials for Tissue and Organ Cryopreservation

Cryopreservation of tissues and organs can bring transformative changes to medicine and medical science. In the past decades, limited progress has been achieved, although cryopreservation of tissues and organs has long been intensively pursued. One key reason is that the cryoprotective agents (CPAs) currently used for cell cryopreservation cannot effectively preserve tissues and organs because of their cytotoxicity and tissue destructive effect as well as the low efficiency in controlling ice formation. In stark contrast, nature has its unique ways of controlling ice formation, and many living organisms can effectively prevent freezing damage. Ice-binding proteins (IBPs) are regarded as the essential materials identified in these living organisms for regulating ice nucleation and growth. Note that controversial results have been reported on the utilization of IBPs and their mimics for the cryopreservation of tissues and organs, that is, some groups revealed that IBPs and mimics exhibited unique superiorities in tissues cryopreservation, while other groups showed detrimental effects. In this perspective, we analyze possible reasons for the controversy and predict future research directions in the design and construction of IBP inspired ice-binding materials to be used as new CPAs for tissue cryopreservation after briefly introducing the cryo-injuries and the challenges of conventional CPAs in the cryopreservation of tissues and organs.

Bioinspired Crowding Inhibits Explosive Ice Growth in Antifreeze Protein Solutions

Antifreeze (glyco)proteins (AF(G)Ps) are naturally evolved ice inhibitors incomparable to any man-made materials, thus, they are gaining intensive interest for cryopreservation and beyond. AF(G)Ps depress the freezing temperature (T_f) noncolligatively below the melting temperature (T_m), generating a thermal hysteresis (TH) gap, within which the ice growth is arrested. However, the ice crystals have been reported to undergo a retaliatory and explosive growth beyond the TH gap, which is lethal to living organisms. Although intensive research has been carried to inhibit such an explosive ice growth, no satisfactory strategy has been discovered until now. Here, we report that crowded solutions mimicking an extracellular matrix (ECM), in which AF(G)Ps are located, can completely inhibit the explosive ice growth. The crowded solutions are the condensates of liquid-liquid phase separation consisting of polyethylene glycol (PEG) and sodium citrate (SC), which possess a nanoscale network and strong hydrogen bond (HB) forming ability, completely different to crowded solutions made of single components, that is, PEG or SC. Due to these unique features, the dynamics of the water is significantly slowed down, and the energy needed for breaking the HB between water molecules is distinctly increased; consequently, ice growth is inhibited as the rate of water molecules joining the ice is substantially reduced. The present work not only opens a new avenue for cryopreservation, but also suggests that the ECM of cold-hardy organisms, which also exhibit great water confining properties, may have a positive effect in protecting the living organisms from freezing damage.

A brief review of applications of antifreeze proteins in cryopreservation and metabolic genetic engineering

Antifreeze proteins (AFPs) confer the ability to survive at subzero temperatures and are found in many different organisms, including fish, plants, and insects. They prevent the formation of ice crystals by non-colligative adsorption to the ice surface and are essential for the survival of organisms in cold environments. These proteins are also widely used for cryopreservation, food technology, and metabolic genetic engineering over a range of sources and recipient cell types. This review summarizes successful applications of AFPs in the cryopreservation of animals, insects, and plants, and discusses challenges encountered in cryopreservation. Applications in metabolic genetic engineering are also described, specifically with the overexpression of AFP genes derived from different organisms to provide freeze protection to sensitive crops seasonally exposed to subzero temperatures. This review will provide information about potential applications of AFPs in the cryopreservation of animals and plants as well as in plant metabolic genetic engineering in hopes of furthering the development of cold-tolerant organisms.

Beetle, Dendroides canadensis, antifreeze proteins increased high temperature survivorship in transgenic fruit flies, Drosophila melanogaster

Paradoxically, some insects have an increased capacity to survive higher temperatures in winter than summer. Possible contributors to this increased heat tolerance in winter could be their sub-zero adaptations (high polyol concentrations, antifreeze proteins, antifreeze glycolipids, etc.). To investigate if a sub-zero adaptation can increase organismal high temperature survivorship, we tested transgenic fruit flies, Drosophila melanogaster, with antifreeze proteins from the fire-colored beetle, Dendroides canadensis (DAFPs). Transgenic Drosophila melanogaster with individual DAFPs-1 and -4 had increased survivorship compared to control flies after 24 h when placed at 35-36.5 °C. The 24 h ULT₅₀ (Upper Lethal Temperature at which 50% mortality occurred) was calculated to be 36.3 °C for DAFP-1 flies, 36.2 °C for DAFP-4 flies, 35.4 °C for wild-type controls, and 34.9 °C for GAL4 controls. The results indicate that DAFPs may have an alternative function in insects and be a contributor in the unexpected phenomenon of increased higher temperature survivorship in winter.

Upper lethal temperatures in three cold-tolerant insects are higher in winter than in summer

Upper lethal temperatures (ULTs) of cold-adapted insect species in winter have not been previously examined. We anticipated that as the lower lethal temperatures (LLTs) decreased (by 20–30°C) with the onset of winter, the ULTs would also decrease accordingly. Consequently, given the recent increases in winter freeze–thaw cycles and warmer winters due to climate change, it became of interest to determine whether ambient temperatures during thaws were approaching ULTs during the cold seasons. However, beetle Dendroides canadensis (Coleoptera: Pyrochroidae) larvae had higher 24 and 48 h ULT50 (the temperature at which 50% mortality occurred) in winter than in summer. The 24 and 48 h ULT50 for D. canadensis in winter were 40.9 and 38.7°C, respectively. For D. canadensis in summer, the 24 and 48 h ULT50 were 36.7 and 36.4°C. During the transition periods of spring and autumn, the 24 h ULT50 was 37.3 and 38.5°C, respectively. While D. canadensis in winter had a 24 h LT50 range between LLT and ULT of 64°C, the summer range was only 41°C. Additionally, larvae of the beetle Cucujus clavipes clavipes (Coleoptera: Cucujidae) and the cranefly Tipula trivittata (Diptera: Tipulidae) also had higher ULTs in winter than in summer. This unexpected phenomenon of increased temperature survivorship at both lower and higher temperatures in the winter compared with that in the summer has not been previously documented. With the decreased high temperature tolerance as the season progresses from winter to summer, it was observed that environmental temperatures are closest to upper lethal temperatures in spring.

Antifreeze proteins govern the precipitation of trehalose in a freezing-avoiding insect at low temperature

The remarkable adaptive strategies of insects to extreme environments are linked to the biochemical compounds in their body fluids. Trehalose, a versatile sugar molecule, can accumulate to high levels in freeze-tolerant and freeze-avoiding insects, functioning as a cryoprotectant and a supercooling agent. Antifreeze proteins (AFPs), known to protect organisms from freezing by lowering the freezing temperature and deferring the growth of ice, are present at high levels in some freeze-avoiding insects in winter, and yet, paradoxically are found in some freeze-tolerant insects. Here, we report a previously unidentified role for AFPs in effectively inhibiting trehalose precipitation in the hemolymph (or blood) of overwintering beetle larvae. We determine the trehalose level (29.6 ± 0.6 mg/mL) in the larval hemolymph of a beetle, Dendroides canadensis, and demonstrate that the hemolymph AFPs are crucial for inhibiting trehalose crystallization, whereas the presence of trehalose also enhances the antifreeze activity of AFPs. To dissect the molecular mechanism, we examine the molecular recognition between AFP and trehalose crystal interfaces using molecular dynamics simulations. The theory corroborates the experiments and shows preferential strong binding of the AFP to the fast growing surfaces of the sugar crystal. This newly uncovered role for AFPs may help explain the long-speculated role of AFPs in freeze-tolerant species. We propose that the presence of high levels of molecules important for survival but prone to precipitation in poikilotherms (their body temperature can vary considerably) needs a companion mechanism to prevent the precipitation and here present, to our knowledge, the first example. Such a combination of trehalose and AFPs also provides a novel approach for cold protection and for trehalose crystallization inhibition in industrial applications.

Animal ice-binding (antifreeze) proteins and glycolipids: an overview with emphasis on physiological function

Ice-binding proteins (IBPs) assist in subzero tolerance of multiple cold-tolerant organisms: animals, plants, fungi, bacteria etc. IBPs include: (1) antifreeze proteins (AFPs) with high thermal hysteresis antifreeze activity; (2) low thermal hysteresis IBPs; and (3) ice-nucleating proteins (INPs). Several structurally different IBPs have evolved, even within related taxa. Proteins that produce thermal hysteresis inhibit freezing by a non-colligative mechanism, whereby they adsorb onto ice crystals or ice-nucleating surfaces and prevent further growth. This lowers the so-called hysteretic freezing point below the normal equilibrium freezing/melting point, producing a difference between the two, termed thermal hysteresis. True AFPs with high thermal hysteresis are found in freeze-avoiding animals (those that must prevent freezing, as they die if frozen) especially marine fish, insects and other terrestrial arthropods where they function to prevent freezing at temperatures below those commonly experienced by the organism. Low thermal hysteresis IBPs are found in freeze-tolerant organisms (those able to survive extracellular freezing), and function to inhibit recrystallization – a potentially damaging process whereby larger ice crystals grow at the expense of smaller ones – and in some cases, prevent lethal propagation of extracellular ice into the cytoplasm. Ice-nucleator proteins inhibit supercooling and induce freezing in the extracellular fluid at high subzero temperatures in many freeze-tolerant species, thereby allowing them to control the location and temperature of ice nucleation, and the rate of ice growth. Numerous nuances to these functions have evolved. Antifreeze glycolipids with significant thermal hysteresis activity were recently identified in insects, frogs and plants.

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).

Identification of a putative antifreeze protein gene that is highly expressed during preparation for winter in the sunn pest, Eurygaster maura

A cDNA library generated from the fat body of field-collected, diapausing adults of the sunn pest, Eurygaster maura revealed the presence of a transcript that encodes a protein that shares the distinct physiochemical and structural features of an insect antifreeze protein. The transcript, which is most abundant in the midgut, accumulates in adults as they leave the fields in late summer and migrate to surrounding mountainous areas to overwinter. Transcript abundance again declines when adults return to the fields the following spring. This winter pattern of abundance suggests that this protein may be critical for winter survival in the cold regions where the bug enters its obligatory diapause.

Antifreeze proteins in the primary urine of larvae of the beetle Dendroides canadensis (Latreille)

To avoid freezing while overwintering beneath the bark of fallen trees, Dendroides canadensis (Coleoptera: Pyrochroidae) larvae produce a family of antifreeze proteins (DAFPs) that are transcribed in specific tissues and have specific compartmental fates. DAFPs and associated thermal hysteresis activity (THA) have been shown previously in hemolymph and midgut fluid, but the presence of DAFPs has not been explored in primary urine, a potentially important site that can contain endogenous ice nucleating compounds that could induce freezing. A maximum mean thermal hysteresis activity of 2.65±0.33°C was observed in primary urine of winter collected D. canadensis larvae. Thermal hysteresis activity in primary urine increased significantly through autumn, peaked in the winter and decreased through spring to levels of 0.2-0.3°C in summer, in a pattern similar to that of hemolymph and midgut fluid. Thermal hysteresis activity was also found in hindgut fluid and excreted rectal fluid suggesting that these larvae not only concentrate AFPs in the hindgut, but also excrete AFPs from the rectal cavity. Based on dafps isolated from Malpighian tubule epithelia, cDNAs were cloned and sequenced, identifying the presence of transcripts encoding 24 DAFP isoforms. Six of these Malpighian tubule DAFPs were known previously, but 18 are new. We also provide functional evidence that DAFPs can inhibit ice nucleators present in insect primary urine. This is potentially critical because D. canadensis larvae die if frozen, and therefore ice formation in any body fluid, including the urine, would be lethal.

Expanding the molecular recognition repertoire of antifreeze polypeptides: effects on nucleoside crystal growth

Despite differences in the crystal structures of ice and nucleosides, antifreeze polypeptides (AFPs) have been demonstrated to inhibit nucleation of 5-methyluridine, cytidine, and inosine and modify the crystal growth of the nucleosides efficiently. The molecular recognition repertoire of AFPs has been expanded to non-ice-like crystalline solids.

Interaction of reduced nicotinamide adenine dinucleotide with an antifreeze protein from Dendroides canadensis: mechanistic implication of antifreeze activity enhancement

Antifreeze proteins (AFPs) found in many organisms can noncolligatively lower the freezing point of water without altering the melting point. The difference between the depressed freezing point and the melting point, termed thermal hysteresis (TH), is usually a measure of the antifreeze activity of AFPs. Certain low molecular mass molecules and proteins can further enhance the antifreeze activity of AFPs. Interaction between an enhancer and arginine is known to play an important role in enhancing the antifreeze activity of an AFP from the beetle Dendroides canadensis (DAFP-1). Here, we examined the enhancement effects of several prevalent phosphate-containing coenzymes on the antifreeze activity of DAFP-1. β-Nicotinamide adenine dinucleotide (reduced) (NADH) is identified as the most efficient enhancer of DAFP-1, which increases the antifreeze activity of DAFP-1 by around 10 times. Examination of the enhancement abilities of a series of NADH analogs and various molecular fragments of NADH reveals that the modifications of nicotinamide generate a series of highly efficient enhancers, though none as effective as NADH itself, and the whole molecular structure of NADH is necessary for its highly efficient enhancement effect. We also demonstrated a 1:1 binding between DAFP-1 and NADH. The binding was characterized by high-performance liquid chromatography (HPLC) using the gel filtration method of Hummel and Dreyer. The data analysis suggests binding between DAFP-1 and NADH with a dissociation constant in the micromolar range. Interactions between DAFP-1 and NADH are discussed along with molecular mechanisms of enhancer action.

Probability of freezing in the freeze-avoiding beetle larvae Cucujus clavipes puniceus (Coleoptera: Cucujidae) from interior Alaska

Freeze-avoiding insects must resist freezing or die. A suite of adaptations to low temperatures, including the production of antifreeze proteins, colligative antifreezes (polyols), and dehydration allows most individuals to prevent freezing below the lowest ambient temperatures experienced in situ; however, there can be a wide variance in the minimum temperatures that individuals of freeze-avoiding species reach before freezing. We used logistic regression to explore factors that affect this variance and to estimate the probability of freezing in larvae of the freeze-avoiding beetle Cucujus clavipes puniceus. We hypothesized that water content ≤0.5 mg mg(-1) dry mass would lead to deep supercooling (avoidance of freezing below -58°C). We found a significant interaction between water content and ambient below-snow temperature and a significant difference between individuals collected from two locations in Alaska: Wiseman and Fairbanks. Individuals collected in Wiseman deep supercooled with greater water content and to a greater range of ambient temperatures than individuals collected in Fairbanks, leading to significantly different lethal water contents associated with 50% probability of freezing.

Arginine, a key residue for the enhancing ability of an antifreeze protein of the beetle Dendroides canadensis

Antifreeze proteins (AFPs) can produce a difference between the nonequilibrium freezing point and the melting point, termed thermal hysteresis (TH). The TH activity of an antifreeze protein (AFP) depends on the specific AFP and its concentration as well as the presence of cosolutes including low molecular mass solutes and/or proteins. We recently identified series of carboxylates and polyols as efficient enhancers for an AFP from the beetle Dendroides canadensis. In this study, we chemically modified DAFP-1 using the arginine-specific reagent 1,2-cyclohexanedione. We demonstrated that 1,2-cyclohexanedione specifically modifies one arginine residue and the modified DAFP-1 loses its enhancing ability completely or partially in the presence of previously identified enhancers. The stronger the enhancement ability of the enhancer on the native DAFP-1, the stronger the enhancement effect of the enhancer on the modified DAFP-1. The weaker enhancers (e.g., glycerol) completely lose their enhancement effect on the modified DAFP-1 due to their inability to compete with 1,2-cyclohexanedione for the arginine residue. Regeneration of the arginine residue using hydroxylamine fully restored the enhancing ability of DAFP-1. These studies indicated that an arginine residue is critical for the enhancing ability of DAFP-1 and the guanidinium group of the arginine residue is important for its interaction with the enhancers, where the general mechanism of arginine-ligand interaction is borne. This work may initiate a complete mechanistic study of the enhancement effect in AFPs.

Expression of biologically active recombinant antifreeze protein His-MpAFP149 from the desert beetle (Microdera punctipennis dzungarica) in Escherichia coli

An insect antifreeze protein gene Mpafp149 was cloned by the RT-PCR approach from the desert beetle Microdera punctipennis dzungarica. Sequence analysis revealed that this gene encoding a protein of 120 amid acids and this protein showed 65-76% homology with other insect antifreeze proteins, the deduced amino acid sequence displays very high similarities in those regions that contain tandem the 12-residue repeats (TCTxSxxCxxAx) domain and the TCT motif. Mpafp149 gene was cloned into pET-28a vector and expressed in Escherichia coli. A single-step purification based on specific binding of histidine residues was achieved. The purified His-MpAFP149 was SDS-PAGE analyzed, showing an atypical migration with molecular weight of about 24 kDa. The expression of His-MpAFP149 was confirmed by Western blot with specific binding to anti-GST-MpAFP149 antibody. The thermal hysteresis activity of the purified recombinant protein was 0.915 degrees C at 0.09 mg/ml, and the supercooling point was -9.6 degrees C at 0.03 mg/ml. In vitro antifreeze activity assay by measuring the survival rate of bacteria at -7 and -20 degrees C respectively, with the protection of His-MpAFP149 showed that the His-MpAFP149 fusion protein was able to enhance the freeze resistance of bacteria.

Effects of polyhydroxy compounds on beetle antifreeze protein activity

Antifreeze proteins (AFPs) noncolligatively depress the nonequilibrium freezing point of a solution and produce a difference between the melting and freezing points termed thermal hysteresis (TH). Some low-molecular-mass solutes can affect the TH values. The TH enhancement effects of selected polyhydroxy compounds including polyols and carbohydrates on an AFP from the beetle Dendroides canadensis were systematically investigated using differential scanning calorimetry (DSC). The number of hydroxyl groups dominates the molar enhancement effectiveness of polyhydroxy compounds having one to five hydroxyl groups. However, the above rule does not apply for polyhydroxy compounds having more than five hydroxyl groups. The most efficient polyhydroxy enhancer identified is trehalose. In a combination of enhancers the strongest enhancer plays the major role in determining the TH enhancement. Mechanistic insights into identification of highly efficient AFP enhancers are discussed.

Antifreeze glycoprotein levels in Antarctic notothenioid fishes inhabiting different thermal environments and the effect of warm acclimation

A quantification method was developed to determine the concentrations of the major antifreeze glycoprotein (AFGP) isoforms in the blood of Antarctic notothenioid fishes. Serum samples were precipitated with 2.5% TCA and the supernatant containing AFGPs were chromatographed on an HPLC size exclusion column and the concentrations of the major AFGP size classes were determined from the areas of the corresponding peaks in the elution profile. Eight species of Antarctic notothenioid fishes were examined and their blood AFGP concentrations varied from 5 to 35 mg/mL. All of these fishes synthesized both the large and small AFGPs, but maintained higher levels of small AFGPs than the large ones in their blood. The species inhabiting more severe water environments (lower temperature and presence of ice) had higher serum AFGP levels than those in milder environments. The cryopelagic Pagothenia borchgrevinki decreased their blood AFGP concentrations in response to warm acclimation, but to a much lower extent in comparison to the antifreeze-bearing fishes in the Northern Hemisphere. After being warm acclimated at +4 degrees C for 16 weeks, the serum concentrations of the small and large AFGPs were decreased by about 60% and 20%, respectively.

A thaumatin-like protein from larvae of the beetle Dendroides canadensis enhances the activity of antifreeze proteins

The levels of thermal hysteresis (antifreeze activity) produced by purified antifreeze proteins (DAFPs) from the larvae of the beetle Dendroides canadensis at endogenous concentrations are lower than what are present in the hemolymph of overwintering larvae. Thermal hysteresis activity of DAFPs is dependent not only on AFP concentration but also on the presence of enhancers that may be either proteins (including other hemolymph DAFPs) or low-molecular mass enhancers such as glycerol. The purpose of this study was to identify endogenous protein enhancers using yeast two-hybrid, co-immunoprecipitation, and finally the enhancement of antifreeze activity. Here we show that a thaumatin-like protein from D. canadensis, until recently known only from plants, significantly enhances the thermal hysteresis of DAFP-1 and -2. Glycerol can further this enhancement, presumably by promoting the interaction of the DAFPs and thaumatin-like protein.

Isolation and characterization of hemolymph antifreeze proteins from larvae of the longhorn beetle Rhagium inquisitor (L.)

We describe a simple and effective procedure to isolate antifreeze proteins (AFPs) from the hemolymph of larvae of the longhorn beetle Rhagium inquisitor, and present some characteristics of their structures. Several AFPs were isolated from the hemolymph of this species by heat and acid extraction followed by cation exchange. The hemolymph contains at least six AFPs ranging in size from 12.5 to 12.8 kDa. Of these, three were separated to purity by the ion exchange step, as indicated by mass spectrometry. The remaining three forms were further separated by size exclusion chromatography, but could not be isolated to purity. All AFPs in the hemolymph of this species appears to have isoelectric points above 8.00. The dominant form, RiAFP(H4), was purified by the ion exchange step. Its amino acid composition reveals a lower level of cysteine and a higher level of threonine, arginine, alanine and glycine than seen in other insect AFPs. Its trypsin fingerprint does not match that of any known protein. It interacts with ice both in the anionic and cationic state.

Antifreeze Proteins of the Beetle Dendroides canadensis Enhance One Another's Activities

Larvae of the beetle Dendroides canadensis produce a family of 13 antifreeze proteins (DAFPs), four of which are in the hemolymph. Antifreeze proteins lower the noncolligative freezing point of water (in the presence of ice) below the melting point, producing a difference between the freezing and melting points termed thermal hysteresis. This activity (THA) is dependent upon DAFP specific activity, concentration, and the presence of enhancers. Enhancers may be low molecular mass enhancers, such as glycerol, or other proteins. The protein enhancers complex with the DAFPs, thereby blocking a larger surface area of the potential seed ice crystal and consequently lowering the freezing point. A yeast two-hybrid screen was performed using certain hemolymph DAFPs as "bait" in an effort to identify endogenous protein enhancers. Among the positive proteins identified as interacting with the bait DAFPs, and confirmed by co-immunoprecipitation, were other DAFPs. When pure DAFPs were added to one another, those identified by the yeast two-hybrid screen as interacting with one another exhibited a synergistic enhancement of thermal hysteresis activity. In contrast, those DAFPs which the screen indicated did not interact failed to enhance one anothers' activities. DAFPs-1 and -2 interact and enhance one another. Point mutations of one of the interacting DAFPs (DAFP-2) indicated that both of the two amino acid residues that differ between DAFPs-1 and -2 were required for interaction. Glycerol enhanced the THA of the DAFPs only when DAFPs known to interact were present in the test solution. Addition of glycerol to a test solution containing only one DAFP did not produce enhancement. Therefore, glycerol enhances activity by stimulating interactions between DAFPs.

Calcium interacts with antifreeze proteins and chitinase from cold-acclimated winter rye

During cold acclimation, winter rye (Secale cereale) plants accumulate pathogenesis-related proteins that are also antifreeze proteins (AFPs) because they adsorb onto ice and inhibit its growth. Although they promote winter survival in planta, these dual-function AFPs proteins lose activity when stored at subzero temperatures in vitro, so we examined their stability in solutions containing CaCl2, MgCl2, or NaCl. Antifreeze activity was unaffected by salts before freezing, but decreased after freezing and thawing in CaCl2 and was recovered by adding a chelator. Ca2+ enhanced chitinase activity 3- to 5-fold in unfrozen samples, although hydrolytic activity also decreased after freezing and thawing in CaCl2. Native PAGE, circular dichroism, and Trp fluorescence experiments showed that the AFPs partially unfold after freezing and thawing, but they fold more compactly or aggregate in CaCl2. Ruthenium red, which binds to Ca(2+)-binding sites, readily stained AFPs in the absence of Ca2+, but less stain was visible after freezing and thawing AFPs in CaCl2. We conclude that the structure of AFPs changes during freezing and thawing, creating new Ca(2+)-binding sites. Once Ca2+ binds to those sites, antifreeze activity, chitinase activity and ruthenium red binding are all inhibited. Because free Ca2+ concentrations are typically low in the apoplast, antifreeze activity is probably stable to freezing and thawing in planta. Ca2+ may regulate chitinase activity if concentrations are increased locally by release from pectin or interaction with Ca(2+)-binding proteins. Furthermore, antifreeze activity can be easily maintained in vitro by including a chelator during frozen storage.

Antifreeze proteins in Alaskan insects and spiders

Prior to this study, antifreeze proteins (AFPs) had not been identified in terrestrial arthropods from the Arctic or anywhere in Alaska. The hemolymph of 75 species of insects and six spiders from interior and arctic Alaska were screened for thermal hysteresis (a difference between the freezing and melting points), characteristic of the presence of AFPs. Eighteen species of insects and three spiders were shown to have AFPs. Ten of the insects with AFPs were beetles including the first species from the families Chrysomelidae, Pythidae, Silphidae and Carabidae. In addition, the first Neuropteran to have AFPs was identified, the lacewing Hemerobius simulans together with the second and third Diptera (the first Tipulids) and the second and third Hemiptera, the stinkbug Elasmostethus interstinctus (the first Pentatomid), and the water strider Limnoporus dissortis (the first Gerrid). Prior to this study, 33 species of insects and three spiders had been reported to have AFPs. Most AFP-producing terrestrial arthropods are freeze avoiding, and the AFPs function to prevent freezing. However, some of the AFP- producing insects identified in this study are known to be freeze tolerant (able to survive freezing) to very low temperatures (-40 to -70 degrees C).