Thermal hysteresis antifreeze proteins in the midgut fluid of overwintering larvae of the beetleDendroides canadensis

Metabolites, ions, and the mechanisms behind seasonal cold hardening of Pyrochroa coccinea (Pyrochroidae) larvae

The larvae of the black headed cardinal beetle Pyrochroa coccinea, overwinters under the bark of dead logs in northern European dioecious forests, and are thus exposed to temperatures below the melting point of their bodily fluids. Here we explore the mechanisms behind their seasonal cold hardening by characterising field samples collected monthly throughout the year. Both the lower lethal temperature and supercooling point dropped as much as 10℃ in the second half of November, reaching values around -15℃ by the beginning of December. This change was accompanied by a 320 mosmol/kg increase in hemolymph osmolality, which is a doubling compared to the summer levels. We used NMR metabolomics to identify and measure the absolute concentrations of the responsible cryoprotective C-H containing metabolites in the hemolymph. The largest increase was found to be in either glucose or trehalose, with an average total increase of 120 mM. Proline, alanine, and choline concentrations were found to increase by around 10 mM each. Contrarily, phosphocholine and phosphoethanolamine were halved, resulting in a total decrease of around 50 mM. These measurements were complemented with ion exchange chromatography measurements. This allowed us to account for all the osmotic pressure in the summer hemolymph, and the measured concentration changes explained as much as 40 % of the observed osmolality increase upon cold hardening. Preliminary results indicate that the remainder may be explained by non-colligative protein contributions.

Synthetic insect antifreeze peptides modify ice crystal growth habit

Synthetic antifreeze peptides based on the hyperactive antifreeze protein modify the shape of ice crystals and show enhanced antifreeze activity with the addition of a small molecule.

Effect of Antifreeze Peptide Pretreatment on Ice Crystal Size, Drip Loss, Texture, and Volatile Compounds of Frozen Carrots

Ice crystal formation is of primary concern to the frozen food industry. In this study, the effects of antifreeze peptides (AFPs) on ice crystal formation were assessed in carrot during freezing and thawing. Three synthetic analogues based on naturally occurring antifreeze peptides were used in this study. The AFPs exhibited modification of ice crystal morphology, confirming their antifreeze activity in vitro. The ability of the synthetic AFPs to minimize drip loss and preserve color, structure, texture, and volatiles of frozen carrot was evaluated using the techniques of SEM, GC-MS, and texture analysis. The results prove the potential of these AFPs to preserve the above characteristics in frozen carrot samples.

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.

Cold tolerance and supercooling capacity in overwintering adults of elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Elm leaf beetle, Xanthogaleruca luteola (Muller) is one of the key pests of elm trees all over the world, and survives winter in reproductive diapause in sheltered locations. Seasonal variation of whole body supercooling points (SCPs), LT50 (temperature at which 50% of the test individuals die) and survival rate after exposure to subzero temperatures were determined in field collected adults during October 2008 to May 2009 and October 2009 to May 2010. The SCP of adults decreased significantly from October (median=-13.8°C) to January (median=-20.7°C) in first year, relatively similar results was observed in the second year. The lowest LT50 was observed in overwintering adults collected in January (-16.81°C) in the first year and December (-15.59°C) in the second year. Mortality at -15°C for 24 h was >70% in early autumn in both years whereas it decreased to lower than 45% in early winter, the highest mortality (100%) was observed in adults collected in May in both years. Cold acclimated adults (30 d, 5°C) in November 2008 exhibited significantly higher SCP (-12.21±0.64°C) than nonacclimated adults (-15.57±1.35°C). A 30-d exposure to 5°C caused >20% mortality in November, while <9% mortality was observed in adults collected in December and January 2008. Overwintering adults died upon freezing and the lower lethal temperatures were within the range of SCP, indicating that X. luteola is a freeze intolerant insect.

Superheating of ice crystals in antifreeze protein solutions

It has been argued that for antifreeze proteins (AFPs) to stop ice crystal growth, they must irreversibly bind to the ice surface. Surface-adsorbed AFPs should also prevent ice from melting, but to date this has been demonstrated only in a qualitative manner. Here we present the first quantitative measurements of superheating of ice in AFP solutions. Superheated ice crystals were stable for hours above their equilibrium melting point, and the maximum superheating obtained was 0.44 degrees C. When melting commenced in this superheated regime, rapid melting of the crystals from a point on the surface was observed. This increase in melting temperature was more appreciable for hyperactive AFPs compared to the AFPs with moderate antifreeze activity. For each of the AFP solutions that exhibited superheating, the enhancement of the melting temperature was far smaller than the depression of the freezing temperature. The present findings clearly show that AFPs adsorb to ice surfaces as part of their mechanism of action, and this absorption leads to protection of ice against melting as well as freezing.

Characterization of antifreeze protein gene expression in summer spruce budworm larvae

Not surprisingly, in the spruce budworm, Choristoneura fumiferana, antifreeze protein (AFP) gene expression is most abundant in the second instar, overwintering stage. However, low level RNA and protein expression was also found in the sixth instar larvae, a summer stage. In situ hybridization further confirmed the presence of AFP mRNA in sixth instar midgut tissues. Sequencing of cDNAs corresponding to "summer-expressed" transcripts revealed an isoform that was not apparent in a cDNA library made to second instar larvae. Although similar to AFP cDNAs obtained from overwintering larvae, this AFP-like isoform (CfAFP6) has two Cys substitutions. Since AFPs from this species fold into a beta-helix that is stabilized by disulfide bonds, it was of interest to determine if this summer-expressed isoform had AFP activity. No thermal hysteresis activity was found when CfAFP6 was cloned and expressed in E. coli, even after in vitro denaturation and refolding. As well, there was no activity detected when the sequence of a known, active isoform was changed to mimic the Cys substitutions in CfAFP6. Since CfAFP6 does not appear to contribute to freeze resistance, its apparent absence in the overwintering second instar should not in itself be considered curious.

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

Antifreeze proteins (AFPs) lower the freezing point of water by a non-colligative mechanism, but do not lower the melting point, therefore producing a difference between the freezing and melting points termed thermal hysteresis. Thermal hysteresis activity (THA) of AFPs from overwintering larvae of the beetle Dendroides canadensis is dependent upon AFP concentration and the presence of enhancers of THA which may be either other proteins or low molecular mass enhancers. The purpose of this study was to determine the relative contributions of endogenous enhancers in winter D. canadensis hemolymph.Winter hemolymph collected over four successive winters (1997-1998 to 2000-2001) was tested. The first three of these winters were the warmest on record in this area, while December of the final year was the coldest on record. Protein and low molecular mass enhancers raised hemolymph THA 60-97% and 35-55%, respectively, based on hemolymph with peak THA for each year collected over the four successive winters. However, the hemolymph AFPs were not maximally enhanced since addition of the potent enhancer citrate (at non-physiologically high levels) resulted in large increases in THA. (13)NMR showed that glycerol was the only low molecular mass solute present in sufficiently high concentrations in the hemolymph to function as an enhancer. Maximum THA appears to be approximately 8.5 degrees C.

Antifreeze and ice nucleator proteins in terrestrial arthropods

Terrestrial arthropods survive subzero temperatures by becoming either freeze tolerant (survive body fluid freezing) or freeze avoiding (prevent body fluid freezing). Protein ice nucleators (PINs), which limit supercooling and induce freezing, and antifreeze proteins (AFPs), which function to prevent freezing, can have roles in both freeze tolerance and avoidance. Many freeze-tolerant insects produce hemolymph PINs, which induce freezing at high subzero temperatures thereby inhibiting lethal intracellular freezing. Some freeze-tolerant species have AFPs that function as cryoprotectants to prevent freeze damage. Although the mechanism of this cryoprotection is not known, it may involve recrystallization inhibition and perhaps stabilization of the cell membrane. Freeze-avoiding species must prevent inoculative freezing initiated by external ice across the cuticle and extend supercooling abilities. Some insects remove PINs in the winter to promote supercooling, whereas others have selected against surfaces with ice-nucleating abilities on an evolutionary time scale. However, many freeze-avoiding species do have proteins with ice-nucleating activity, and these proteins must be masked in winter. In the beetle Dendroides canadensis, AFPs in the hemolymph and gut inhibit ice nucleators. Also, hemolymph AFPs and those associated with the layer of epidermal cells under the cuticle inhibit inoculative freezing. Two different insect AFPs have been characterized. One type from the beetles D. canadensis and Tenebrio molitor consists of 12- and 13-mer repeating units with disulfide bridges occurring at least every six residues. The spruce budworm AFP lacks regular repeat units. Both have much higher activities than any known AFPs.

Thermal hysteresis proteins

Extreme environments present a wealth of biochemical adaptations. Thermal hysteresis proteins (THPs) have been found in vertebrates, invertebrates, plants, bacteria and fungi and are able to depress the freezing point of water (in the presence of ice crystals) in a non-colligative manner by binding to the surface of nascent ice crystals. The THPs comprise a disparate group of proteins with a variety of tertiary structures and often no common sequence similarities or structural motifs. Different THPs bind to different faces of the ice crystal, and no single mechanism has been proposed to account for THP ice binding affinity and specificity. Experimentally THPs have been used in the cryopreservation of tissues and cells and to induce cold tolerance in freeze susceptible organisms. THPs represent a remarkable example of parallel and convergent evolution with different proteins being adapted for an anti-freeze role.

Ice nucleation and antinucleation in nature

Plants and ectothermic animals use a variety of substances and mechanisms to survive exposure to subfreezing temperatures. Proteinaceous ice nucleators trigger freezing at high subzero temperatures, either to provide cold protection from released heat of fusion or to establish a protective extracellular freezing in freeze-tolerant species. Freeze-avoiding species increase their supercooling potential by removing ice nucleators and accumulating polyols. Terrestrial invertebrates and polar marine fish stabilize their supercooled state by means of noncolligatively acting antifreeze proteins. Some organisms also depress their body fluid melting point to ambient temperature by evaporation and/or solute accumulation.

Interactions between desiccation resistance, host-plant contact and the thermal biology of a leaf-dwelling sub-antarctic caterpillar, Embryonopsis halticella (Lepidoptera: Yponomeutidae)

During May 1997 thermal tolerance, supercooling point (SCP), low and high temperature survival, and desiccation resistance were examined in field-fresh Embryonopsis halticella Eaton larvae from Marion Island. SCPs were also examined in acclimated larvae, larvae starved for seven days, larvae within their leaf mines, and in larvae exposed to ice crystals. Field-fresh larvae had a critical minimum temperature (CT(Min)) and critical maximum temperature (CT(Max)) of 0 degrees C and 39.7 degrees C, respectively. Mean SCP of field-fresh caterpillars was -20.5 degrees C and this did not change with starvation. Field-fresh larvae did not survive freezing and their lower lethal temperatures (70% mortality below -21 degrees C) and survival of exposure to constant low temperatures (100% mortality after 12hrs at -19 degrees C) indicated that they are moderately chill tolerant. SCP frequency distributions were unimodal for field-fresh larvae, but became bimodal at higher acclimation temperatures. Contact with ice-crystals caused an increase in SCP (-6.5 degrees C), but contact with the host plant had less of an effect at higher subzero temperatures. It appears that the remarkable desiccation resistance of the larvae is selected for by the absence of a boundary layer surrounding their host plant, caused by constant high winds. This suggests that the low SCPs of E. halticella larvae may have evolved as a consequence of pronounced desiccation resistance.

Photoaffinity labeling of the 1,25-dihydroxyvitamin D-3 receptor

Underivatized 1,25-dihydroxy[26,27-3H]vitamin D-3 was successfully used to photoaffinity label the 1,25-dihydroxyvitamin D-3 receptor. The covalent incorporation of tritium into the receptor protein was induced by ultraviolet irradiation of the receptor-1,25-dihydroxy[26,27-3H]vitamin D-3 complex in crude pig intestinal nuclear extract. The amount of incorporated label increased with increasing time of irradiation and was dependent on light of wavelengths 220-280 nm. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography were used to demonstrate that label was incorporated primarily into the 1,25-dihydroxyvitamin D-3 receptor. In addition, the label incorporation was eliminated by competition with a 100-fold excess nonradioactive 1,25-dihydroxyvitamin D-3, indicating that the label was specific for the steroid binding site. Since 1,25-(OH)2[26,27-3H]vitamin D-3 is readily available and requires no special precautions for its preparation and handling, it should be a useful photoaffinity label for future studies of the receptor.

Enhancement of insect antifreeze protein activity by antibodies

Antifreeze proteins, produced by many cold water marine teleost fish and terrestrial arthropods (insects, spiders, etc.), inhibit ice crystal growth by a non-colligative mechanism, probably by adsorbing onto the surface of potential seed ice crystals and thereby blocking growth at preferred growth sites. In this study it is demonstrated that the activity of two insect antifreeze proteins is greatly increased by the addition of specific rabbit polyclonal antibodies to the antifreezes. A model is presented which suggests that the enhancement occurs because the antifreeze-antibody complex, being much larger than the antifreeze protein alone (a minimal 7-8-fold increase in size), blocks a larger area of the ice crystal surface and extends further above the surface, thus requiring the temperature to be further lowered before crystal growth proceeds. This idea is further supported by the finding that addition of goat anti-rabbit IgG to the antifreeze protein + anti-antifreeze protein antibody complexes further enhanced activity.