Lipid unsaturation determines the interaction of AFP type I with model membranes during thermotropic phase transitions

The ice-binding site of antifreeze protein irreversibly binds to cell surface for its hypothermic protective function

Antifreeze proteins (AFPs) are multifunctional polypeptides that adsorb onto ice crystals to inhibit their growth and onto cells to protect them from nonfreezing hypothermic damage. However, the mechanism by which AFP exerts its hypothermic cell protective (HCP) function remains uncertain. Here, we assessed the HCP function of three types of fish-derived AFPs (type I, II, and III AFPs) against human T-lymphoblastic lymphoma by measuring the survival rate (%) of the cells after preservation at 4 °C for 24 h. All AFPs improved the survival rate in a concentration-dependent manner, although the HCP efficiency was inferior for type III AFP compared to other AFPs. In addition, after point mutations were introduced into the ice-binding site (IBS) of a type III AFP, HCP activity was dramatically increased, suggesting that the IBS of AFP is involved in cell adsorption. Significantly, high HCP activity was observed for a mutant that exhibited poorer antifreeze activity, indicating that AFP exerts HCP- and ice-binding functions through a different mechanism. We next incubated the cells in an AFP-containing solution, replaced it with pure EC solution, and then preserved the cells, showing that no significant reduction in the cell survival rate occurred for type I and II AFPs even after replacement. Thus, these AFPs irreversibly bind to the cells at 4 °C, and only tightly adsorbed AFP molecules contribute towards the cell-protection function.

Thermal profiles reveal stark contrasts in properties of biological membranes from heart among Antarctic notothenioid fishes which vary in expression of hemoglobin and myoglobin

Antarctic notothenioids are noted for extreme stenothermy, yet underpinnings of their thermal limits are not fully understood. We hypothesized that properties of ventricular membranes could explain previously observed differences among notothenioids in temperature onset of cardiac arrhythmias and persistent asystole. Microsomes were prepared using ventricles from six species of notothenioids, including four species from the hemoglobin-less (Hb-) family Channichthyidae (icefishes), which also differentially express cardiac myoglobin (Mb), and two species from the (Hb+) Nototheniidae. We determined membrane fluidity and structural integrity by quantifying fluorescence depolarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and leakage of 5(6)-carboxyfluorescein, respectively, over a temperature range from ambient (0 °C) to 20 °C. Compositions of membrane phospholipids and cholesterol contents were also quantified. Membranes from all four species of icefishes exhibited greater fluidity than membranes from the red-blooded species N. coriiceps. Thermal sensitivity of fluidity did not vary among species. The greatest thermal sensitivity to leakage occurred between 0 and 5 °C for all species, while membranes from the icefish, Chaenocephalus aceratus (Hb-/Mb-) displayed leakage that was nearly 1.5-fold greater than leakage in N. coriiceps (Hb+/Mb+). Contents of phosphatidylethanolamine (PE) were approximately 1.5-fold greater in icefishes than in red-blooded fishes, and phospholipids had a higher degree of unsaturation in icefishes than in Hb + notothenioids. Cholesterol contents were lowest in Champsocephalus gunnari (Hb-/Mb-) and highest in the two Hb+/Mb + species, G. gibberifrons and N. coriiceps. Our results reveal marked differences in membrane properties and indicate a breach in membrane fluidity and structural integrity at a lower temperature in icefishes than in red-blooded notothenioids.

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 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.

The effect of lipid composition, bilayer phase and temperature on the uptake of hematoporphyrin by liposomal membranes

In this study we investigated, spectroscopically, the binding of hematoporphyrin (HP) to non-charged lipid vesicles as a function of temperature and the molecular structure of the phospholipid. The temperature dependence of partitioning was employed to evaluate the thermodynamic parameters of the process. We studied the binding of HP to liposomes composed of different phospholipids: natural lecithin and three chemically defined phosphatidylcholines: dimiristoyl-phosphatidylcholine (DMPC), 1-palmitoyl-2-myristoyl-phosphatidylcholine (PMPC) and 1-stearoyl-2-myristoyl-phosphatidylcholine (SMPC), at different temperatures. The last three lipids differ only in the length of the fatty acid on 1 position of the glycerol backbone. Consequently, they have different phase transition temperatures and different order parameters. For SMPC, PMPC and DMPC, we checked the effect of temperatures above and below the phase transition while for lecithin, whose phase transition temperature is well below 0 °C, only temperatures above the phase transition could be tested. A very distinct effect of the phase transition on the binding constant was observed. Below this temperature a dramatic decrease in the binding was observed as the temperature was increased. Above the phase transition, the effect of temperature declined and the changes were minor compared to the changes observed when the bilayers undergo the solid-gel phase transition. Differences in HP binding to the various bilayers were attributed to the differences in the order parameters of DMPC, PMPC, SMPC and lecithin bilayers.

Emerging Role for Use of Liposomes in the Biopreservation of Red Blood Cells

SUMMARY: Biopreservation is the process of maintaining the integrity and functionality of cells held outside the native environment for extended storage times. The development of red blood cell (RBC) biopreservation techniques that maintain in vitro RBC viability and function represents the foundation of modern blood banking. The biopreservation of RBCs for clinical use can be categorized based on the techniques used to achieve biologic stability, including hypothermic storage and cryopreservation. This review will examine the emerging role of liposomes in the RBC biopreservation, including the incorporation of liposomes into RBC membranes as an effective approach for minimizing RBC hypothermic storage membrane lesion and use of liposomes as a permeabilization strategy for the intracellular accumulation of novel intracellular cryoprotectants. Integration of current biopreservation research with blood banking practices offers enormous potential for future improvements of safety and efficacy of RBC transfusion.

Cryoprotection and cryosterilization effects of type I antifreeze protein on E. coli cells

To establish the effects of type I antifreeze protein (AFP) on E. coli cells, we have focused on the survival rate of the E. coli cells using type I AFP at various concentrations under rapid cooling conditions using liquid N2 at atmospheric or low pressure. The survival rate of E. coli was enhanced by the addition of type I AFP at a concentration of 10 microg/ml, and its value shifted from 0.73% to 2.96%. When the concentration of type I AFP was 100 microg/ml, the cell survival rate markedly decreased to 0.090%. This low survival rate was further decreased (0.022%) by the application of the same freeze-thaw treatment for four times. Also, the effect of type I AFP as a bactericidal agent did not vary according to the varying initial cell densities from 10(4) to 10(8) cells / ml. Furthermore, the effects of using type I AFP at 1.0 MPa with N2 gas under conditions of low pressure and low oxygen tension using a simple device were examined. When the actions of type I AFP as a cryoprotectant were stimulated, the survival rate of the E. coil cells increased to 57.8%. In addition, the bactericidal effect of type I AFP at 100 micro g/ml of protein concentration could also be enhanced. The survival rate using 100 g/ml of type I AFP under low pressure was 0.35% of that using 10 microg/ml under the same conditions. This is the first report on the cryoprotectant and cryosterilization effects of type I AFP of E. coli cells under various conditions.

Cryoprotective effects of antifreeze proteins delivered into zebrafish embryos

Fish embryo cryopreservation, which is useful in aquaculture or biodiversity conservation, is still far from being achieved. Structural barriers reduce the entrance of cryoprotectants into embryo compartments. Previous studies demonstrated a better ability for freezing in Arctic species which naturally express antifreeze proteins (AFPs). In this study, AFPs were delivered in early zebrafish embryos by incubation in media containing protein. Their cryoprotective effects were then analyzed. Chilling sensitivity was evaluated at 4 degrees C and -10 degrees C. Survival rates significantly increased in embryos incorporating AFPI and kept at -10 degrees C. To analyze their effects on cryopreservation, 5-somite embryos were vitrified. Incorporation of AFPI reduced the percentage of embryos that collapsed at thawing (14.2% of AFPI-treated embryos and 48.9% of controls). Cellular damage caused by vitrification was assessed after thawing by cell dissociation and further analysis of cell survival in culture (SYBR-14/IP labeling). The percentage of viable cells at thawing ranged from 25 to 50%, considered incompatible with embryo development. Cells recovered from frozen-control embryos did not survive in culture. However, the incorporation of AFPs allowed survival similar to that of cells recovered from non-frozen embryos. Blastomere cryopreservation trials incorporating AFPI in the extender also demonstrated a significant increase in viability after freezing. Our findings demonstrated that delivery of AFPs into zebrafish embryos by incubation in media containing protein at early stages is a simple and harmless method that increases cryoprotection of the cellular compartment. This beneficial effect is also noticed in blastomeres, encouraging their use in further protocols for embryo cryopreservation.

Incorporation of antifreeze proteins into zebrafish embryos by a non-invasive method

The cryopreservation of fish embryos is a challenge because of their structure, with multiple compartments and permeability barriers, and their high chilling sensitivity. Vitrification at advanced developmental stages is considered to be the more promising option. Nevertheless, all reported attempts have failed. Previous studies demonstrated a better ability for freezing in species that naturally express antifreeze proteins (AFPs). These proteins have been delivered into other fish embryos using time-consuming techniques like microinjection. In the present study, the introduction of FITC labelled AFPs was assayed in zebrafish embryos at early developmental stages (from 2-cell to high blastula stage), before the formation of the yolk syncytial layer, by an easy and non-invasive method and evaluated by fluorescence and confocal microscopy. Incubation with AFPs at 128-cell or high blastula stage provides incorporation of the protein in 50-90% of embryos without affecting hatching. Incubation in media containing protein is a simple, harmless and effective method which makes it possible to treat several embryos at the same time. AFPs remain located in derivatives from marginal blastomeres: the yolk syncytial layer, the most cryosensitive and impermeable barrier, and different digestive organs. Our findings demonstrate that delivery of AFP type I and AFP type III into zebrafish embryos by incubation in media containing protein is a simple and harmless method that may improve cryoprotection of the cellular compartment.

Spectrophotometric measurement of intraliposomal trehalose

Trehalose, a non-reducing glucose disaccharide found at high concentrations in many species of anhydrobiotic organisms, shows significant promise in protecting cellular viability and structural integrity during freezing and desiccation. As mammalian cell membranes are impermeable to trehalose, extensive efforts have been taken to introduce trehalose into mammalian cells. In this study, we report on the characterization of trehalose-containing liposomes, with focus on the entrapment of trehalose inside liposomes, as the first step in establishing liposomes as a delivery system in the biopreservation field. Liposomes were synthesized by hydrating a phospholipid/cholesterol lipid bilayer with 200-400 mM trehalose buffer and repeatedly extruding the lipid suspension to form unilamellar vesicles. The trehalose content of the liposomal lysate was determined spectrophotometrically using a commercial kit Megazyme and confirmed with HPLC measurements. The number of liposomes was calculated from the phosphate content of the liposomal preparation and an estimated number of lipid molecules in a 401+/-8 nm liposome. Based on an intraliposomal trehalose content, the calculated liposomal encapsulation efficiency of 200 mM trehalose liposomes was of 92+/-0.7%. This value was in agreement with the 300 and 400 mM trehalose liposomes (91.1+/-8.2% and 102.1+/-9.4%, respectively). The Megazyme method for trehalose measurement is an inexpensive and sensitive technique that does not require specialized instrumentation or extensive technical expertise. Therefore, it can be used to enhance current efforts in the development of alternative strategies for the cryo- and lyoprotection of mammalian cells.

Antifreeze proteins at the ice/water interface: three calculated discriminating properties for orientation of type I proteins

Antifreeze proteins (AFPs) protect many plants and organisms from freezing in low temperatures. Of the different AFPs, the most studied AFP Type I from winter flounder is used in the current computational studies to gain molecular insight into its adsorption at the ice/water interface. Employing molecular dynamics simulations, we calculate the free energy difference between the hydrophilic and hydrophobic faces of the protein interacting with ice. Furthermore, we identify three properties of Type I "antifreeze" proteins that discriminate among these two orientations of the protein at the ice/water interface. The three properties are: the "surface area" of the protein; a measure of the interaction of the protein with neighboring water molecules as determined by the number of hydrogen bond count, for example; and the side-chain orientation angles of the threonine residues. All three discriminants are consistent with our free energy results, which clearly show that the hydrophilic protein face orientations toward the ice/water interface, as hypothesized from experimental and ice/vacuum simulations, are incorrect and support the hypothesis that the hydrophobic face is oriented toward the ice/water interface. The adsorption free energy is calculated to be 2-3 kJ/mol.

The effect of hydrophobic analogues of the type I winter flounder antifreeze protein on lipid bilayers

The effect of four synthetic analogues of the 37-residue winter flounder type I antifreeze protein (AFP), which contain four Val, Ala or Ile residues in place of Thr residues at positions 2, 13, 24 and 37 and two additional salt bridges, on the binary lipid system prepared from a 1:1 mixture of the highly unsaturated DGDG and saturated DMPC has been determined using FTIR spectroscopy. In contrast to the natural protein, which increases the thermotropic phase transition, the Thr, Val and Ala analogues decreased the thermotropic phase transitions of the liposomes by 2.2 degrees Celsius, 3.4 degrees Celsius and 2.4 degrees Celsius, while the Ile analogue had no effect on the transition. Experiments performed using perdeuterated DMPC showed that the Ala and Thr peptides interacted preferentially with the DGDG in the lipid mixture, while the Val peptide showed no preference for either lipid. The results are consistent with interactions involving the hydrophobic face of type I AFPs and model bilayers, i.e. the same face of the protein that is responsible for antifreeze properties. The different effects correlate with the helicity of the peptides and suggest that the solution conformation of the peptides has a significant role in determining the effects of the peptides on thermotropic membrane phase transitions.