The stability during low-temperature storage of an antifreeze protein isolated from the roots of cold-acclimated carrots

Structural diversity of marine anti-freezing proteins, properties and potential applications: a review

Cold-adapted organisms, such as fishes, insects, plants and bacteria produce a group of proteins known as antifreeze proteins (AFPs). The specific functions of AFPs, including thermal hysteresis (TH), ice recrystallization inhibition (IRI), dynamic ice shaping (DIS) and interaction with membranes, attracted significant interest for their incorporation into commercial products. AFPs represent their effects by lowering the water freezing point as well as preventing the growth of ice crystals and recrystallization during frozen storage. The potential of AFPs to modify ice growth results in ice crystal stabilizing over a defined temperature range and inhibiting ice recrystallization, which could minimize drip loss during thawing, improve the quality and increase the shelf-life of frozen products. Most cryopreservation studies using marine-derived AFPs have shown that the addition of AFPs can increase post-thaw viability. Nevertheless, the reduced availability of bulk proteins and the need of biotechnological techniques for industrial production, limit the possible usage in foods. Despite all these drawbacks, relatively small concentrations are enough to show activity, which suggests AFPs as potential food additives in the future. The present work aims to review the results of numerous investigations on marine-derived AFPs and discuss their structure, function, physicochemical properties, purification and potential applications.

Marine Antifreeze Proteins: Structure, Function, and Application to Cryopreservation as a Potential Cryoprotectant

Antifreeze proteins (AFPs) are biological antifreezes with unique properties, including thermal hysteresis(TH),ice recrystallization inhibition(IRI),and interaction with membranes and/or membrane proteins. These properties have been utilized in the preservation of biological samples at low temperatures. Here, we review the structure and function of marine-derived AFPs, including moderately active fish AFPs and hyperactive polar AFPs. We also survey previous and current reports of cryopreservation using AFPs. Cryopreserved biological samples are relatively diverse ranging from diatoms and reproductive cells to embryos and organs. Cryopreserved biological samples mainly originate from mammals. Most cryopreservation trials using marine-derived AFPs have demonstrated that addition of AFPs can improve post-thaw viability regardless of freezing method (slow-freezing or vitrification), storage temperature, and types of biological sample type.

Antifreeze proteins in naturally cold acclimated leaves of Drimys angustifolia, Senecio icoglossus, and Eucalyptus ssp

Summary Antifreeze proteins (AFPs) present in plants may inhibit ice recrystallization even at low concentrations, and show potential application to many frozen foods. This study evaluated the presence of antifreeze proteins in naturally cold acclimated and non-acclimated leaves of Drimys angustifolia, Senecio icoglossus and Eucalyptus ssp. No proteins were detected in apoplastic extracts of Eucalyptus ssp. Extracts of cold acclimated and non-acclimated S. icoglossus showed protein concentrations of 42.89 and 17.76 µg mL-1, both with bands between 25 and 37 kDa in the SDS-PAGE. However, they did not inhibit recrystallization. The extract of cold acclimated D. angustifolia contained a protein concentration of 95.17 µg mL-1, almost five times higher than the extract of non-acclimated D. angustifolia. In the extract of cold acclimated D. angustifolia, there was presence of ice recrystallization inhibitors. This extract showed a protein band just below 37 kDa and another more intense band between 20 and 25 kDa. It is the first time that the presence of antifreeze proteins in this species is being described.

Revisão: Proteínas anticongelantes – uma tecnologia emergente para o congelamento de alimentos

Um dos métodos mais tradicionais na conservação de alimentos, o congelamento também pode alterar de forma significativa as características do produto. Grandes cristais de gelo provocam alteração na textura e/ou danos a membranas e componentes celulares. As técnicas de congelamento rápido formam cristais de gelo menores do que o processo lento, porém as flutuações de temperatura durante a distribuição e transporte podem promover o crescimento dos cristais. Esse processo é conhecido como recristalização e é uma barreira na utilização do congelamento como método de conservação em muitos casos. O uso de crioprotetores tradicionais, como a sacarose, é uma alternativa limitada, uma vez que concentrações elevadas são requeridas. Na década de 1970, foi descrita em peixes de águas frias uma classe de proteínas que, em baixa concentração, pode interagir e influenciar o crescimento do cristal de gelo. Elas foram chamadas de proteínas anticongelantes (PACs), sendo encontradas também em plantas, animais e micro-organismos ambientados a baixas temperaturas. Essas proteínas podem intervir no processo de formação do núcleo inicial do gelo, reduzir o ponto de congelamento da água, ou, ainda, inibir a recristalização, principalmente para PACs de vegetais. Há diversos trabalhos publicados e algumas patentes registradas para o uso de PACs em diversos alimentos, como lácteos, carnes, massas, frutas e hortaliças, conservando de melhor forma as características originais do alimento. Atualmente, o custo ainda é uma barreira para utilização comercial das PACs. Contudo, a descoberta de novas fontes pode reduzir seu custo e tornar essas proteínas uma ferramenta efetiva na manutenção da textura de alimentos congelados. Baseada em trabalhos que avaliaram aspectos químicos das PACs e exemplos de sua aplicação, esta revisão tem como objetivo principal apresentar as características gerais das PACs e discutir sobre sua utilização.

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.

Thermodynamic stability of a cold-adapted protein, type III antifreeze protein, and energetic contribution of salt bridges

A thermodynamic analysis of a cold-adapted protein, type III anti-freeze protein (AFP), was carried out. The results indicate that the folding equilibrium of type III AFP is a reversible, unimolecular, two-state process with no populated intermediates. Compared to most mesophilic proteins whose folding is two-state, the psychrophilic type III AFP has a much lower thermodynamic stability at 25 degrees C, approximately 3 kcal/mol, and presents a remarkably downshifted stability-temperature curve, reaching a maximum of 5 kcal/mol around 0 degrees C. Type III AFPs contain few and non-optimally distributed surface charges relative to their mesophilic homologs, the C-terminal domains of sialic acid synthases. We used thermodynamic double mutant cycles to evaluate the energetic role of every surface salt bridge in type III AFP. Two isolated salt bridges provided no contribution to stability, while the Asp36-Arg39 salt bridge, involved in a salt bridge network with the C-terminal carboxylate, had a substantial contribution (approximately 1 kcal/mol). However, this contribution was more than counteracted by the destabilizing effect of the Asp36 carboxylate itself, whose removal led to a net 30% increase in stability at 25 degrees C. This study suggests that type III AFPs may have evolved for a minimally acceptable stability at the restricted, low temperature range (around 0 degrees C) at which AFPs must function. In addition, it indicates that salt bridge networks are used in nature also for the stability of psychrophilic proteins, and has led to a type III AFP variant of increased stability that could be used for biotechnological purposes.

Purification and characterisation of an antifreeze protein from Forsythia suspensa (L.)

Recrystallisation inhibition (RI) activity has been isolated from cold-acclimated Forsythia suspensa bark and leaves, which is stable when boiled, and not sensitive to reducing agents. The antifreeze activity has been purified to a single 20 kDa protein, using anion exchange, hydroxyapatite chromatography, and gel filtration. The protein is abundant in forsythia bark with 0.5microg pure protein obtained from 35 g bark. RI activity is seen with as little as 6 microg ml(-1) protein. Sequence homology was seen with dehydrins, and forsythia AFP contains the Y-segment, a conserved region found in many dehydrins.

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.

Vitrification of large tissues with dielectric warming: biological problems and some approaches to their solution

If large pieces of tissue and organs are to be successfully stored at low temperatures, some means must be found to minimize the disruption of extracellular structures by the ice that develops during conventional cryopreservation methods. The use of sufficiently high concentrations of cryoprotectant (CPA) to vitrify rather than freeze the tissue is a possible solution to this problem, and the retention of function of embryos and elastic arteries after vitrification suggests that some cells and tissues at least can withstand exposure to the high concentrations of CPA necessary for this process to occur. There are, however, additional problems in applying vitrifying techniques to bulky tissues and organs. These are related to the additional time required for tissue equilibration of CPA to occur and the consequences for toxic injury, the difficulty in achieving sufficiently rapid and uniform cooling rates to produce the required glassy state, and the even more rapid and uniform warming rates that are necessary to avoid devitrification. Non-uniformity of temperature will increase the risk of mechanical stresses and fractures developing in the glass during rapid warming. This paper reviews possible strategies and the progress that has been made in overcoming these problems. This will include the permeation of CPA mixtures into whole tissues and possibilities for reducing their toxicity by the inclusion of adjuncts such as ice inhibitors and sugars. The warming of tissues by dielectric heating is currently the only practical means by which sufficiently rapid rates can be achieved in bulky tissues given that the tolerable limits of CPA concentration will most likely be insufficient to prevent the development of ice nuclei during cooling. The biological effects of microwaves are reviewed and their effectiveness in producing the required uniformity in warming of tissue models of various shapes are discussed.