Skin-type antifreeze protein from the shorthorn sculpin, Myoxocephalus scorpius. Expression and characterization of a Mr 9, 700 recombinant protein

Fish antifreeze protein origin in sculpins by frameshifting within a duplicated housekeeping gene

Antifreeze proteins (AFPs) are found in a variety of marine cold-water fishes where they prevent freezing by binding to nascent ice crystals. Their diversity (types I, II, III and antifreeze glycoproteins), as well as their scattered taxonomic distribution hint at their complex evolutionary history. In particular, type I AFPs appear to have arisen in response to the Late Cenozoic Ice Age that began ~ 34 million years ago via convergence in four different groups of fish that diverged from lineages lacking this AFP. The progenitor of the alanine-rich α-helical type I AFPs of sculpins has now been identified as lunapark, an integral membrane protein of the endoplasmic reticulum. Following gene duplication and loss of all but three of the 15 exons, the final exon, which encoded a glutamate- and glutamine-rich segment, was converted to an alanine-rich sequence by a combination of frameshifting and mutation. Subsequent gene duplications produced numerous isoforms falling into four distinct groups. The origin of the flounder type I AFP is quite different. Here, a small segment from the original antiviral protein gene was amplified and the rest of the coding sequence was lost, while the gene structure was largely retained. The independent origins of type I AFPs with up to 83% sequence identity in flounder and sculpin demonstrate strong convergent selection at the level of protein sequence for alanine-rich single alpha helices that bind to ice. Recent acquisition of these AFPs has allowed sculpins to occupy icy seawater niches with reduced competition and predation from other teleost species.

Identification and Functional Characterization of Antifreeze Protein and Its Mutants in Dendroctonus armandi (Coleoptera: Curculionidae: Scolytinae) Larvae Under Cold Stress

Dendroctonus armandi (Tsai and Li) (Coleoptera: Curculionidae: Scolytinae) is considered to be the most destructive forest pest in the Qinling and Bashan Mountains of China. Low winter temperatures limit insect's populations, distribution, activity, and development. Insects have developed different strategies such as freeze-tolerance and freeze-avoidance to survive in low temperature conditions. In the present study, we used gene cloning, real-time polymerase chain reaction (PCR), RNA interference (RNAi), and heterologous expression to study the function of the D. armandi antifreeze protein gene (DaAFP). We cloned the 800 bp full-length cDNA encoding 228 amino acids of DaAFP and analyzed its structure using bioinformatics analysis. The DaAFP amino acid sequence exhibited 24-86% similarity with other insect species. The expression of DaAFP was high in January and in the larvae, head, and midgut of D. armandi. In addition, the expression of DaAFP increased with decreasing temperature and increasing exposure time. RNAi analysis also demonstrated that AFP plays an important role in the cold tolerance of overwintering larvae. The thermal hysteresis and antifreeze activity assay of DaAFP and its mutants indicated that the more regular the DaAFP threonine-cystine-threonine (TXT) motif, the stronger the antifreeze activity. These results suggest that DaAFP plays an essential role as a biological cryoprotectant in overwintering D. armandi larvae and provides a theoretical basis for new pest control methods.

Freeze Tolerance in Sculpins (Pisces; Cottoidea) Inhabiting North Pacific and Arctic Oceans: Antifreeze Activity and Gene Sequences of the Antifreeze Protein

Many marine species inhabiting icy seawater produce antifreeze proteins (AFPs) to prevent their body fluids from freezing. The sculpin species of the superfamily Cottoidea are widely found from the Arctic to southern hemisphere, some of which are known to express AFP. Here we clarified DNA sequence encoding type I AFP for 3 species of 2 families (Cottidae and Agonidae) belonging to Cottoidea. We also examined antifreeze activity for 3 families and 32 species of Cottoidea (Cottidae, Agonidae, and Rhamphocottidae). These fishes were collected in 2013–2015 from the Arctic Ocean, Alaska, Japan. We could identify 8 distinct DNA sequences exhibiting a high similarity to those reported for Myoxocephalus species, suggesting that Cottidae and Agonidae share the same DNA sequence encoding type I AFP. Among the 3 families, Rhamphocottidae that experience a warm current did not show antifreeze activity. The species inhabiting the Arctic Ocean and Northern Japan that often covered with ice floe showed high activity, while those inhabiting Alaska, Southern Japan with a warm current showed low/no activity. These results suggest that Cottoidea acquires type I AFP gene before dividing into Cottidae and Agonidae, and have adapted to each location with optimal antifreeze activity level.

Sequencing and Expression Characterization of Antifreeze Protein Maxi-Like in Apis cerana cerana

Antifreeze proteins (AFPs) are biological cryoprotectants with unique properties that play a crucial role in regulating the molecular mechanisms governing cold resistance in insects. To identify and characterize Apis cerana cerana AFP (AcerAFP), we cloned the full-length cDNA of AcerAFP and examined its expression patterns in A. cerana cerana. A nucleotide alignment analysis showed that the entire coding region of AcerAFP is 1095 bp and encodes a polypeptide of 365 amino acids. The amino acid sequence of this protein exhibits 63–96% homology with AFP homologs from other hymenopterans. α-helices form the main secondary and tertiary structures of AcerAFP, which is similar to the molecular structure of fish AFP type-I. The expression profiles of AcerAFP revealed that expression was tissue, sex, and developmentally specific. In response to cold stress, the mRNA and protein expression of AcerAFP were both induced by low temperatures, and were also related to the concentrations of several cryoprotectants, including glucose, glycerin, glutamic acid, cysteine, histidine, alanine, and methionine. In addition, we found that the knockdown of AcerAFP by RNA interference remarkably increased the total freezing temperature of hemolymph in A. cerana cerana, where levels of AcerAFP mRNA were correlated with the expression of most antifreeze-related proteins. Taken together, these results suggest that AcerAFP plays an essential role as a biological cryoprotectant in honeybees, and is in turn regulated by small cryoprotectants and antifreeze-related proteins.

Helical antifreeze proteins have independently evolved in fishes on four occasions

Alanine-rich α-helical (type I) antifreeze proteins (AFPs) are produced by a variety of fish species from three different orders to protect against freezing in icy seawater. Interspersed amongst and within these orders are fishes making AFPs that are completely different in both sequence and structure. The origin of this variety of types I, II, III and antifreeze glycoproteins (AFGPs) has been attributed to adaptation following sea-level glaciations that occurred after the divergence of most of the extant families of fish. The presence of similar types of AFPs in distantly related fishes has been ascribed to lateral gene transfer in the case of the structurally complex globular type II lectin-like AFPs and to convergent evolution for the AFGPs, which consist of a well-conserved tripeptide repeat. In this paper, we examine the genesis of the type I AFPs, which are intermediate in complexity. These predominantly α-helical peptides share many features, such as putative capping structures, Ala-richness and amphipathic character. We have added to the type I repertoire by cloning additional sequences from sculpin and have found that the similarities between the type I AFPs of the four distinct groups of fishes are not borne out at the nucleotide level. Both the non-coding sequences and the codon usage patterns are strikingly different. We propose that these AFPs arose via convergence from different progenitor helices with a weak affinity for ice and that their similarity is dictated by the propensity of specific amino acids to form helices and to align water on one side of the helix into an ice-like pattern.

Optimization of the pilot-scale production of an ice-binding protein by fed-batch culture of Pichia pastoris

Ice-binding proteins (IBPs) can bind to the ice crystal and inhibit its growth. Because this property of IBPs can increase the freeze-thaw survival of cells, IBPs have attracted the attention from industries for their potential use in biotechnological applications. However, their use was largely hampered by the lack of the large-scale recombinant production system. In this study, the codon-optimized IBP from Leucosporidium sp. (LeIBP) was constructed and subjected to high-level expression in methylotrophic Pichia pastoris system. In a laboratory-scale fermentation (7 L), the optimal induction temperature and pH were determined to be 25 °C and 6.0, respectively. Further, employing glycerol fed-batch phase prior to methanol induction phase enhanced the production of recombinant LelBP (rLeIBP) by ∼100 mg/l. The total amount of secreted proteins at these conditions (25 °C, pH 6.0, and glycerol fed-batch phase) was ∼443 mg/l, 60 % of which was rLeIBP, yielding ∼272 mg/l. In the pilot-scale fermentation (700 L) under the same conditions, the yield of rLeIBP was 300 mg/l. To our best knowledge, this result reports the highest production yield of the recombinant IBP. More importantly, the rLeIBP secreted into culture media was stable and active for 6 days of fermentation. The thermal hysteresis (TH) activity of rLeIBP was about 0.42 °C, which is almost the same to those reported previously. The availability of large quantities of rLeIBP may accelerate further application studies.

Epithelial dominant expression of antifreeze proteins in cunner suggests recent entry into a high freeze-risk ecozone

Most marine teleost fishes residing in a high freeze-risk ecozone, such as the coastal waters of Newfoundland during winter, avoid freezing by secreting high concentrations of antifreeze proteins (AFP) into their blood plasma where they can bind to and prevent the growth of ice that enter the fish. Cunner (Tautogolabrus adspersus), which overwinter in such shallow waters are the only known exception. Although this species does produce type I AFP, the plasma levels are too low to be of value as a freeze protectant. Southern and Northern blot analyses carried out in this study establish that the cunner AFP genes belong to a multigene family that is predominantly expressed in external epithelia (skin and gill filaments). These results support the hypothesis that the survival of cunner in icy waters is attributable in part to epithelial AFP that help block ice propagation into their interior milieu. In contrast to the cunner, heterospecifics occupying the same habitat have greater freeze protection because they produce AFP in the liver for export to the plasma as well as in external epithelia. Since the external epithelia would be the first tissue to come into contact with ice it is possible that one of the earliest steps involved in the evolution of freeze resistant fish could have been the expression of AFP in tissues such as the skin. We suggest that this epithelial-dominant AFP expression represents a primitive stage in AFP evolution and propose that cunner began to inhabit "freeze-risk ecozones" more recently than heterospecifics.

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.

Type I antifreeze proteins expressed in snailfish skin are identical to their plasma counterparts

Type I antifreeze proteins (AFPs) are usually small, Ala-rich alpha-helical polypeptides found in right-eyed flounders and certain species of sculpin. These proteins are divided into two distinct subclasses, liver type and skin type, which are encoded by separate gene families. Blood plasma from Atlantic (Liparis atlanticus) and dusky (Liparis gibbus) snailfish contain type I AFPs that are significantly larger than all previously described type I AFPs. In this study, full-length cDNA clones that encode snailfish type I AFPs expressed in skin tissues were generated using a combination of library screening and PCR-based methods. The skin clones, which lack both signal and pro-sequences, produce proteins that are identical to circulating plasma AFPs. Although all fish examined consistently express antifreeze mRNA in skin tissue, there is extreme individual variation in liver expression - an unusual phenomenon that has never been reported previously. Furthermore, genomic Southern blot analysis revealed that snailfish AFPs are products of multigene families that consist of up to 10 gene copies per genome. The 113-residue snailfish AFPs do not contain any obvious amino acid repeats or continuous hydrophobic face which typify the structure of most other type I AFPs. These structural differences might have implications for their ice-crystal binding properties. These results are the first to demonstrate a dual liver/skin role of identical type I AFP expression which may represent an evolutionary intermediate prior to divergence into distinct gene families.

Hyperactive antifreeze protein in flounder species. The sole freeze protectant in American plaice

The recent discovery of a large hyperactive antifreeze protein in the blood plasma of winter flounder has helped explain why this fish does not freeze in icy seawater. The previously known, smaller and much less active type I antifreeze proteins cannot by themselves protect the flounder down to the freezing point of seawater. The relationship between the large and small antifreezes has yet to be established, but they do share alanine-richness (> 60%) and extensive alpha-helicity. Here we have examined two other righteye flounder species for the presence of the hyperactive antifreeze, which may have escaped prior detection because of its lability. Such a protein is indeed present in the yellowtail flounder judging by its size, amino acid composition and N-terminal sequence, along with the previously characterized type I antifreeze proteins. An ortholog is also present in American plaice based on the above criteria and its high specific antifreeze activity. This protein was purified and shown to be almost fully alpha-helical, highly asymmetrical, and susceptible to denaturation at room temperature. It is the only detectable antifreeze protein in the blood plasma of the American plaice. Because this species appears to lack the smaller type I antifreeze proteins, the latter may have evolved by descent from the larger antifreeze.

Type I Antifreeze Proteins: Possible Origins from Chorion and Keratin Genes in Atlantic Snailfish

Type I antifreeze proteins (AFPs) are alanine-rich alpha-helical polypeptides found in some species of right-eye flounders, sculpin, and snailfish. In this study, a shorthorn sculpin skin type I cDNA clone was used to probe an Atlantic snailfish liver cDNA library in order to locate expressed genes corresponding to snailfish plasma AFPs. Clones isolated from the cDNA library had sections with substantial amino acid and nucleotide sequence similarity to snailfish type I AFPs. However, further analysis revealed that the positives were actually three different liver-expressed proteins-two were eggshell proteins, while the third was a type II keratin. We propose that a shift in reading frame could produce alanine-rich candidate AFPs with possible antifreeze activity or ice crystal modification properties. Furthermore, it is plausible that one or more of the liver-expressed proteins represent the progenitors of snailfish type I AFPs.

Isolation and purification of antifreeze proteins from skin tissues of snailfish, cunner and sea raven

Antifreeze proteins/polypeptides (AFPs), which are found in diverse species of marine fish, are grouped into four distinct classes (types I-IV). The discovery of skin-specific type I AFPs established that this class contains distinct isoforms, liver-type and skin-type, which are encoded by separate gene families. In this study, type I AFPs were isolated and partially characterized from skin tissues of Atlantic snailfish (Liparis atlanticus) and cunner (Tautogolabrus adspersus). Interestingly, evidence from this study indicates that snailfish type I AFPs synthesized in skin tissues are identical to those circulating in their blood plasma. Furthermore, type II AFPs that are identical to those expressed in liver for export into blood were purified from sea raven (Hemitripterus americanus) skin tissue extracts. It is clear that epithelial tissues are an important source for antifreeze expression to enhance the complement of AFPs that protect fish from freezing in extreme cold environments. In addition, the evidence generated in this study demonstrates that expression of AFPs in fish skin is a widespread phenomenon that is not limited to type I proteins.

Fish can be first--advances in fish transgenesis for commercial applications

Over the past 15 years researchers have generated stable lines of several species of transgenic fish important for aquaculture. 'All-fish' growth hormone (GH) gene constructs and antifreeze protein (AFP) genes have been successfully introduced into the fish genome resulting in a significant acceleration of growth rate and an increase in cold and freeze tolerance. However, neither gene modification is completely understood; there are still questions to be resolved. Expression rates are still low, producing variable growth enhancement rates and less than desired levels of freeze resistance. Transgene strategies are also being developed to provide improved pathogen resistance and modified metabolism for better utilization of the diet. Additional challenges are to tailor the genetically modified fish strains to prevent release of the modified genes into the environment.

Antifreeze proteins of teleost fishes

Marine teleosts at high latitudes can encounter ice-laden seawater that is approximately 1 degrees C colder than the colligative freezing point of their body fluids. They avoid freezing by producing small antifreeze proteins (AFPs) that adsorb to ice and halt its growth, thereby producing an additional non-colligative lowering of the freezing point. AFPs are typically secreted by the liver into the blood. Recently, however, it has become clear that AFP isoforms are produced in the epidermis (skin, scales, fin, and gills) and may serve as a first line of defense against ice propagation into the fish. The basis for the adsorption of AFPs to ice is something of a mystery and is complicated by the extreme structural diversity of the five antifreeze types. Despite the recent acquisition of several AFP three-dimensional structures and the definition of their ice-binding sites by mutagenesis, no common ice-binding motif or even theme is apparent except that surface-surface complementarity is important for binding. The remarkable diversity of antifreeze types and their seemingly haphazard phylogenetic distribution suggest that these proteins might have evolved recently in response to sea level glaciation occurring just 1-2 million years ago in the northern hemisphere and 10-30 million years ago around Antarctica. Not surprisingly, the expression of AFP genes from different origins can also be quite dissimilar. The most intensively studied system is that of the winter flounder, which has a built-in annual cycle of antifreeze expression controlled by growth hormone (GH) release from the pituitary in tune with seasonal cues. The signal transduction pathway, transcription factors, and promoter elements involved in this process are just beginning to be characterized.

Isolation and characterization of type I antifreeze proteins from Atlantic snailfish (Liparis atlanticus) and dusky snailfish (Liparis gibbus)

Antifreeze proteins (AFPs) were isolated from the blood plasma of Atlantic snailfish Liparis atlanticus and dusky snailfish Liparis gibbus, which belong to the Teleost family Cyclopteridae, a close relative of sculpins. Using a combination of gel filtration chromatography and reversed-phase HPLC, proteins were purified to individual peaks. Atlantic snailfish plasma contained two different proteins (MW=9344, 9415) while dusky snailfish plasma contained five protein isoforms (MW=9514-9814), as determined by mass spectrometry. Further characterization revealed that these proteins are rich in alanine (>50 mol%), and have alpha-helical secondary structure that can undergo reversible thermal denaturation. Thermal hysteresis activities of these proteins were similar to each other but lower than the major type I AFPs from winter flounder. Results of this study have indicated that although the AFPs from snailfish are significantly larger than previously described type I AFPs, they share enough characteristics to be classified in this group.

Cutaneous biology and diseases of fish

The normal structure and function of the piscine integument reflects the adaptation of the organism to the physical, chemical, and biological properties of the aquatic environment, and the natural history of the organism. Because of the intimate contact of fish with the environment, cutaneous disease is relatively more common in fish than in terrestrial vertebrates and is one of the primary disease conditions presented to the aquatic animal practitioner. However, cutaneous lesions are generally nonspecific and may be indicative of disease that is restricted to the integument or a manifestation of systemic disease. Regardless, a gross and microscopic examination of the integument is simple to perform, but is highly diagnostic and should always be included in the routine diagnostic effort of the aquatic animal practitioner, especially since various ancillary diagnostic procedures are either not practical or lack predictive value in fish. The purpose of this article is to provide an overview of normal cutaneous biology prior to consideration of specific cutaneous diseases in fish.

Isolation and characterization of skin-type, type I antifreeze polypeptides from the longhorn sculpin, Myoxocephalus octodecemspinosus

The antifreeze polypeptides (AFPs) are found in several marine fish and have been grouped into four distinct biochemical classes (type I-IV). Recently, the new subclass of skin-type, type I AFPs that are produced intracellularly as mature polypeptides have been identified in the winter flounder (Pleuronectes americanus) and the shorthorn sculpin (Myoxocephalus scorpius). This study demonstrates the presence of skin-type AFPs in the longhorn sculpin (Myoxocephalus octodecemspinosus), which produces type IV serum AFPs. Using polymerase chain reaction-based methods, a clone that encoded for a type I AFP was identified. The clone lacked a signal sequence, indicating that the mature polypeptide is produced in the cytosol. A recombinant protein was produced in Escherichia coli and antifreeze activity was characterized. Four individual Ala-rich polypeptides with antifreeze activity were isolated from the skin tissue. One polypeptide was completely sequenced by tandem MS. This study provides the first evidence of a fish species that produces two different biochemical classes of antifreeze proteins (type I and type IV), and enforces the notion that skin-type AFPs are a widespread biological phenomenon in fish.

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.

NMR analysis of type III antifreeze protein intramolecular dimer. Structural basis for enhanced activity

The structure of a new antifreeze protein (AFP) variant, RD3, from antarctic eel pout (Rhigophila dearborni) with enhanced activity has been determined for the first time by nuclear magnetic resonance spectroscopy. RD3 comprises a unique translational topology of two homologous type III AFP globular domains, each containing one flat, ice binding plane. The ice binding plane of the N domain is located approximately 3.5 A "behind" that of the C domain. The two ice binding planes are located laterally with an angle of 32 +/- 12 degrees between the planes. These results suggest that the C domain plane of RD3 binds first to the ice [1010] prism plane in the <0001> direction, which induces successive ice binding of the N domain in the <0101> direction. This manner of ice binding caused by the unique structural topology of RD3 is thought to be crucial for the significant enhancement of antifreeze activity, especially at low AFP concentrations.

A comprehensive evaluation of the effects and mechanisms of antifreeze proteins during low-temperature preservation

During the past 10 years, it has become clear that the effects of antifreeze proteins (AFPs) on cell viability and on thermodynamic properties during low-temperature preservation are complex, even controversial. In this paper, these studies are reviewed systematically and some conclusions are drawn. It is shown that AFPs can display both protective and cytotoxic actions and both nucleation of ice and inhibition of ice crystal growth, depending on several factors; these include the specific storage protocol, the dose and type of AFP, the composition and concentration of cryoprotectant, and the features of the biological material. A novel model, incorporating some recent findings concerning these proteins, is proposed to explain this dual effect of AFPs during cryopreservation. AFP-ice complexes have some affinity interactions with cell membranes and with many other molecules present in cryopreservation solutions. When the intensity of these interactions reaches a certain level, the AFP-ice complexes may be induced to aggregate, thereby inducing ice nucleation and loss of the ability to inhibit recrystallization.