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

A Novel Form of Arginine-Chitosan as Nanoparticles Efficient for siRNA Delivery into Mouse Leukemia Cells

The modification of chitosan (CS) has greatly expanded its application in the field of medicine. In this study, low-molecular-weight chitosan was modified with arginine (Arg) by a simple method. The identification by the Fourier transform infrared spectra (FTIR) showed that Arg was successfully covalently attached to the CS. Interestingly, Arg-CS was identified as nanoparticles by atomic force microscopy (AFM) and transmission electron microscopy (TEM), whose particle size was 75.76 ± 12.07 nm based on Dynamic Light Scattering (DLS) characterization. Then, whether the prepared Arg-CS nanoparticles could encapsulate and deliver siRNA safely was investigated. Arg-CS was found to be able to encapsulate siRNAs in vitro via electrostatic interaction with siRNA; the Arg-CS/siRNA complex was safe for L1210 leukemia cells. Therefore, modification of chitosan by Arg produces novel nanoparticles to deliver siRNA into leukemia cells. This is the first time to identify Arg-CS as nanoparticles and explore their ability to deliver Rhoa siRNA into T-cell acute lymphoblastic leukemia (T-ALL) cells to advance therapies targeting Rhoa in the future.

Submilligram Level of Beetle Antifreeze Proteins Minimize Cold-Induced Cell Swelling and Promote Cell Survival

Hypothermic (cold) preservation is a limiting factor for successful cell and tissue transplantation where cell swelling (edema) usually develops, impairing cell function. University of Wisconsin (UW) solution, a standard cold preservation solution, contains effective components to suppress hypothermia-induced cell swelling. Antifreeze proteins (AFPs) found in many cold-adapted organisms can prevent cold injury of the organisms. Here, the effects of a beetle AFP from Dendroides canadensis (DAFP-1) on pancreatic β-cells preservation were first investigated. As low as 500 µg/mL, DAFP-1 significantly minimized INS-1 cell swelling and subsequent cell death during 4 °C preservation in UW solution for up to three days. However, such significant cytoprotection was not observed by an AFP from Tenebrio molitor (TmAFP), a structural homologue to DAFP-1 but lacking arginine, at the same levels. The cytoprotective effect of DAFP-1 was further validated with the primary β-cells in the isolated rat pancreatic islets in UW solution. The submilligram level supplement of DAFP-1 to UW solution significantly increased the islet mass recovery after three days of cold preservation followed by rewarming. The protective effects of DAFP-1 in UW solution were discussed at a molecular level. The results indicate the potential of DAFP-1 to enhance cell survival during extended cold preservation.

Toxicity Profiles and Protective Effects of Antifreeze Proteins From Insect in Mammalian Models

Antifreeze proteins (AFPs), found in many cold-adapted organisms, can protect them from cold and freezing damages and have thus been considered as additional protectants in current cold tissue preservation solutions that generally include electrolytes, osmotic agents, colloids and antioxidants, to reduce the loss of tissue viability associated with cold-preservation. Due to the lack of toxicity profile studies on AFPs, their inclusion in cold preservation solutions has been a trial-and-error process limiting the development of AFPs' application in cold preservation. To assess the feasibility of translating the technology of AFPs for mammalian cell cold or cryopreservation, we determined the toxicity profile of two highly active beetle AFPs, DAFP1 and TmAFP, from Dendroides canadensis and Tenebrio molitor in this study. Toxicity was examined on a panel of representative mammalian cell lines including testicular spermatogonial stem cells and Leydig cells, macrophages, and hepatocytes. Treatments with DAFP1 and TmAFP at up to 500μg/mL for 48 and 72hours were safe in three of the cell lines, except for a 20% decrease in spermatogonia treated with TmAFP. However, both AFPs at 500μg/mL or below reduced hepatocyte viability by 20 to 40% at 48 and 72h. At 1000μg/mL, DAFP1 and TmAFP reduced viability in most cell lines. While spermatogonia and Leydig cell functions were not affected by 1000μg/mL DAFP1, this treatment induced inflammatory responses in macrophages. Adding 1000μg/ml DAFP1 to rat kidneys stored at 4°C for 48hours protected the tissues from cold-related damage, based on tissue morphology and gene and protein expression of two markers of kidney function. However, DAFP1 and TmAFP did not prevent the adverse effects of cold on kidneys over 72hours. Overall, DAFP1 is less toxic at high dose than TmAFP, and has potential for use in tissue preservation at doses up to 500μg/mL. However, careful consideration must be taken due to the proinflammatory potential of DAFP1 on macrophages at higher doses and the heighten susceptibility of hepatocytes to both AFPs.

Complete inhibition of a polyol nucleation by a micromolar biopolymer additive

Preventing spontaneous crystallization of supersaturated solutions by additives is of critical interest to successful process design and implementation, with numerous applications in chemical, pharmaceutical, medical, pigment, and food industries, but challenges remain in laboratory and industry settings and fundamental understanding is lacking. When copresented with antifreeze proteins (AFPs), otherwise spontaneously crystallizing osmolytes are maintained at high supersaturations for months in over-wintering organisms. Thus, we here explore the inhibition phenomenon by AFPs, using persistent crystallization of a common sugar alcohol, D-mannitol, as a case study. We report experimentally that DAFP1, an insect AFP, completely inhibits D-mannitol nucleation. Computer simulations reveal a new mechanism for crystallization inhibition where the population of the crystal-forming conformers are selectively bound and randomized in solution by hydrogen bonding to the protein surface. These results highlight the advantages of using natural polymers to address crystallization inhibition challenges and suggest new strategies in controlling the nucleation processes.

Discovery of Hyperactive Antifreeze Protein from Phylogenetically Distant Beetles Questions Its Evolutionary Origin

Beetle hyperactive antifreeze protein (AFP) has a unique ability to maintain a supercooling state of its body fluids, however, less is known about its origination. Here, we found that a popular stag beetle Dorcus hopei binodulosus (Dhb) synthesizes at least 6 isoforms of hyperactive AFP (DhbAFP). Cold-acclimated Dhb larvae tolerated -5 °C chilled storage for 24 h and fully recovered after warming, suggesting that DhbAFP facilitates overwintering of this beetle. A DhbAFP isoform (~10 kDa) appeared to consist of 6-8 tandem repeats of a 12-residue consensus sequence (TCTxSxNCxxAx), which exhibited 3 °C of high freezing point depression and the ability of binding to an entire surface of a single ice crystal. Significantly, these properties as well as DNA sequences including the untranslated region, signal peptide region, and an AFP-encoding region of Dhb are highly similar to those identified for a known hyperactive AFP (TmAFP) from the beetle Tenebrio molitor (Tm). Progenitor of Dhb and Tm was branched off approximately 300 million years ago, so no known evolution mechanism hardly explains the retainment of the DNA sequence for such a lo-ng divergence period. Existence of unrevealed gene transfer mechanism will be hypothesized between these two phylogenetically distant beetles to acquire this type of hyperactive AFP.

Effectiveness of Small Interfering RNA Delivery via Arginine-Rich Polyethylenimine-Based Polyplex in Metastatic and Doxorubicin-Resistant Breast Cancer Cells

Poor cellular uptake, rapid degradation in the presence of serum, and inefficient transfection are some of the major barriers in achieving therapeutic efficacy of naked small interfering RNAs (siRNAs). We investigated the efficacy of the polyplex formulated using our synthesized polymer, polyethylene glycol (PEG)-modified l-arginine oligo(-alkylaminosiloxane) that is grafted with poly(ethyleneimine) (PEI) for siRNA delivery. We hypothesized that the polyplex formulated using the polymer with a balanced composition of PEI for siRNA condensation and its protection, PEG for polyplex stability and to minimize the PEI-associated toxicity, and with arginine facilitating cellular uptake would overcome the aforementioned issues with siRNA delivery. We tested our hypothesis using antiluciferase siRNA in luciferase-expressing metastatic breast cancer cells (MDA-MB-231-Luc-D3H2LN) and anti-ABCB1 siRNA against an efflux membrane protein, ABCB1, in doxorubicin (DOX)-resistant breast cancer cells (MCF-7/Adr). The results demonstrated that the polyplex at an optimal nucleotide/polymer ratio is stable in the presence of excess polyanions, has no cellular toxicity, and protects siRNA from RNase degradation. Transfection of MDA-MB-231-Luc-D3H2LN cells with antiluciferase siRNA polyplex showed almost complete knockdown of luciferase expression. In MCF-7/Adr cells, transfection with anti-ABCB1 siRNA effectively downregulated its target efflux protein, ABCB1; increased cellular uptake of DOX; and enhanced its cytotoxic effect. However, the cotreatment did not completely overcome drug resistance, suggesting that further optimization is needed and/or a mechanism(s) other than the efflux protein ABCB1 may be involved in drug resistance. In conclusion, our polyplex is effective for siRNA delivery and can be explored for different therapeutic applications.

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.

Ice-Binding Proteins in Plants

Sub-zero temperatures put plants at risk of damage associated with the formation of ice crystals in the apoplast. Some freeze-tolerant plants mitigate this risk by expressing ice-binding proteins (IBPs), that adsorb to ice crystals and modify their growth. IBPs are found across several biological kingdoms, with their ice-binding activity and function uniquely suited to the lifestyle they have evolved to protect, be it in fishes, insects or plants. While IBPs from freeze-avoidant species significantly depress the freezing point, plant IBPs typically have a reduced ability to lower the freezing temperature. Nevertheless, they have a superior ability to inhibit the recrystallization of formed ice. This latter activity prevents ice crystals from growing larger at temperatures close to melting. Attempts to engineer frost-hardy plants by the controlled transfer of IBPs from freeze-avoiding fish and insects have been largely unsuccessful. In contrast, the expression of recombinant IBP sequences from freeze-tolerant plants significantly reduced electrolyte leakage and enhanced freezing survival in freeze-sensitive plants. These promising results have spurred additional investigations into plant IBP localization and post-translational modifications, as well as a re-evaluation of IBPs as part of the anti-stress and anti-pathogen axis of freeze-tolerant plants. Here we present an overview of plant freezing stress and adaptation mechanisms and discuss the potential utility of IBPs for the generation of freeze-tolerant crops.

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.

Comparative study of hydration shell dynamics around a hyperactive antifreeze protein and around ubiquitin

The hydration layer surrounding a protein plays an essential role in its biochemical function and consists of a heterogeneous ensemble of water molecules with different local environments and different dynamics. What determines the degree of dynamical heterogeneity within the hydration shell and how this changes with temperature remains unclear. Here, we combine molecular dynamics simulations and analytic modeling to study the hydration shell structure and dynamics of a typical globular protein, ubiquitin, and of the spruce budworm hyperactive antifreeze protein over the 230-300 K temperature range. Our results show that the average perturbation induced by both proteins on the reorientation dynamics of water remains moderate and changes weakly with temperature. The dynamical heterogeneity arises mostly from the distribution of protein surface topographies and is little affected by temperature. The ice-binding face of the antifreeze protein induces a short-ranged enhancement of water structure and a greater slowdown of water reorientation dynamics than the non-ice-binding faces whose effect is similar to that of ubiquitin. However, the hydration shell of the ice-binding face remains less tetrahedral than the bulk and is not "ice-like". We finally show that the hydrogen bonds between water and the ice-binding threonine residues are particularly strong due to a steric confinement effect, thereby contributing to the strong binding of the antifreeze protein on ice crystals.

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.

Arginine-rich polyplexes for gene delivery to neuronal cells

Neuronal gene therapy potentially offers an effective therapeutic intervention to cure or slow the progression of neurological diseases. However, neuronal cells are difficult to transfect with nonviral vectors, and in vivo their transport across the blood-brain barrier (BBB) is inefficient. We synthesized a series of arginine-rich oligopeptides, grafted with polyethyleneimine (PEI) and modified with a short-chain polyethylene glycol (PEG). We hypothesized that the arginine would enhance cellular uptake and transport of these polyplexes across the BBB, with PEG imparting biocompatibility and "stealth" properties and PEI facilitating DNA condensation and gene transfection. The optimized composition of the polyplexes demonstrated hemocompatibility with red blood cells, causing no lysis or aggregation, and showed significantly better cytocompatibility than PEI in vitro. Polyplexes formulated with luciferase-expressing plasmid DNA could transfect rat primary astrocytes and neurons in vitro. Confocal imaging data showed efficient cellular uptake of DNA and its sustained intracellular retention and nuclear localization with polyplexes. Intravenous administration of the optimized polyplexes in mice led to gene expression in the brain, which upon further immunohistochemical analysis demonstrated gene expression in neurons. In conclusion, we have successfully designed a nonviral vector for in vitro and in vivo neuronal gene delivery.

Investigation of the Ice-Binding Site of an Insect Antifreeze Protein Using Sum-Frequency Generation Spectroscopy

We study the ice-binding site (IBS) of a hyperactive antifreeze protein from the beetle Dendroides canadensis (DAFP-1) using vibrational sum-frequency generation spectroscopy. We find that DAFP-1 accumulates at the air-water interface due to the hydrophobic character of its threonine-rich IBS while retaining its highly regular β-helical fold. We observe a narrow band at 3485 cm(-1) that we assign to the O-H stretch vibration of threonine hydroxyl groups of the IBS. The narrow character of the 3485 cm(-1) band suggests that the hydrogen bonds between the threonine residues at the IBS and adjacent water molecules are quite similar in strength, indicating that the IBS of DAFP-1 is extremely well-ordered, with the threonine side chains showing identical rotameric confirmations. The hydrogen-bonded water molecules do not form an ordered ice-like layer, as was recently observed for the moderate antifreeze protein type III. It thus appears that the antifreeze action of DAFP-1 does not require the presence of ordered water but likely results from the direct binding of its highly ordered array of threonine residues to the ice surface.

Molecular recognition of methyl α-D-mannopyranoside by antifreeze (glyco)proteins

Antifreeze proteins and glycoproteins [AF(G)Ps] have been well-known for more than three decades for their ability to inhibit the growth and recrystallization of ice through binding to specific ice crystal faces, and they show remarkable structural compatibility with specific ice crystal faces. Here, we show that the crystal growth faces of methyl α-D-mannopyranoside (MDM), a representative pyranose sugar, also show noteworthy structural compatibility with the known periodicities of AF(G)Ps. We selected fish AFGPs (AFGP8, AFGP1-5), and a beetle AFP (DAFP1) with increasing antifreeze activity as potential additives for controlling MDM crystal growth. Similar to their effects on ice growth, the AF(G)Ps can inhibit MDM crystal growth and recrystallization, and more significantly, the effectiveness for the AF(G)Ps are well correlated with their antifreeze activity. MDM crystals grown in the presence of AF(G)Ps are smaller and have better defined shapes and are of higher quality as indicated by single crystal X-ray diffraction and polarized microscopy than control crystals, but no new polymorphs of MDM were identified by single crystal X-ray diffraction, solid-state NMR, and attenuated total reflectance infrared spectroscopy. The observed changes in the average sizes of the MDM crystals can be related to the changes in the number of the MDM nuclei in the presence of the AF(G)Ps. The critical free energy change differences of the MDM nucleation in the absence and presence of the additives were calculated. These values are close to those of the ice nucleation in the presence of AF(G)Ps suggesting similar interactions are involved in the molecular recognition of MDM by the AF(G)Ps. To our knowledge this is the first report where AF(G)Ps have been used to control crystal growth of carbohydrates and on AFGPs controlling non-ice-like crystals. Our finding suggests MDM might be a possible alternative to ice for studying the detailed mechanism of AF(G)P-crystal interactions. The relationships between AF(G)Ps and carbohydrate binding proteins are also discussed. The structural compatibility between AF(G)Ps and growing crystal faces demonstrated herein adds to the repertoire of molecular recognition by AF(G)Ps, which may have potential applications in the sugar, food, pharmaceutical, and materials industries.

Antifreeze protein-induced selective crystallization of a new thermodynamically and kinetically less preferred molecular crystal

The formation of a new, dihydrate crystalline form of 5-methyluridine (m(5)U) was selectively induced by a protein additive, antifreeze protein (AFP) in a highly efficient manner (in 10(-6) molar scale, whereas known kinetic additives need 0.1 molar scale). The hemihydrate form (form I, the only previously known crystalline form of m(5)U) and the dihydrate form of m(5)U (form II) obtained herein were characterized using X-ray crystallography and differential scanning calorimetry (DSC). Compared to form I, remarkably, form II is thermodynamically and kinetically less preferred. The presence of AFP can selectively inhibit the appearance of form I and hence allows the growth of form II, the pure form of which cannot grow directly from m(5) U supersaturated solutions under the same conditions. An explanation supported by both experimental and theoretical results is provided for the AFP-induced selection process. Implications on AFP-induced ice shape changes are also discussed. Control of crystallization from supersaturated solutions is of great interest in both fundamental research and practical applications in fields like chemistry, pharmacology and materials science. These findings suggest that crystallization processes with AFPs could be valuable for selective growth of hydrates and polymorphs of important pharmaceutical compounds.

Long-range protein-water dynamics in hyperactive insect antifreeze proteins

Antifreeze proteins (AFPs) are specific proteins that are able to lower the freezing point of aqueous solutions relative to the melting point. Hyperactive AFPs, identified in insects, have an especially high ability to depress the freezing point by far exceeding the abilities of other AFPs. In previous studies, we postulated that the activity of AFPs can be attributed to two distinct molecular mechanisms: (i) short-range direct interaction of the protein surface with the growing ice face and (ii) long-range interaction by protein-induced water dynamics extending up to 20 Å from the protein surface. In the present paper, we combine terahertz spectroscopy and molecular simulations to prove that long-range protein-water interactions make essential contributions to the high antifreeze activity of insect AFPs from the beetle Dendroides canadensis. We also support our hypothesis by studying the effect of the addition of the osmolyte sodium citrate.

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.

Thermodynamic Analysis of Thermal Hysteresis: Mechanistic Insights into Biological Antifreezes

Antifreeze proteins (AFPs) bind to ice crystal surfaces and thus inhibit the ice growth. The mechanism for how AFPs suppress freezing is commonly modeled as an adsorption-inhibition process by the Gibbs-Thomson effect. Here we develop an improved adsorption-inhibition model for AFP action based on the thermodynamics of impurity adsorption on the crystal surfaces. We demonstrate the derivation of a realistic relationship between surface protein coverage and the protein concentration. We show that the improved model provides a quantitatively better fit to the experimental antifreeze activities of AFPs from distinct structural classes, including fish and insect AFPs, in a wide range of concentrations. Our theoretical results yielded the adsorption coefficients of the AFPs on ice, suggesting that, despite the distinct difference in their antifreeze activities and structures, the affinities of the AFPs to ice are very close and the mechanism of AFP action is a kinetically controlled, reversible process. The applications of the model to more complex systems along with its potential limitations are also discussed.

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.