Antifreeze proteins (AFPs) or ice structuring proteins refer to a class of
polypeptides
Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.
A p ...
produced by certain
animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s,
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s,
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
and
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
that permit their survival in temperatures below the freezing point of water. AFPs bind to small
ice crystals
Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust.
Formation
The hugely symmetric shapes are due to depositional growth, n ...
to inhibit the growth and
recrystallization of ice that would otherwise be fatal.
There is also increasing evidence that AFPs interact with mammalian cell membranes to protect them from cold damage. This work suggests the involvement of AFPs in cold
acclimatization
Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), ...
.
Non-colligative properties
Unlike the widely used automotive antifreeze,
ethylene glycol
Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
, AFPs do not lower freezing point in proportion to concentration. Rather, they work in a non
colligative
In chemistry, colligative properties are those properties of solutions that depend on the ratio of the number of solute particles to the number of solvent particles in a solution, and not on the nature of the chemical species present. The number r ...
manner. This phenomenon allows them to act as an antifreeze at concentrations 1/300th to 1/500th of those of other dissolved solutes. Their low concentration minimizes their effect on
osmotic pressure.
The unusual properties of AFPs are attributed to their selective affinity for specific crystalline ice forms and the resulting blockade of the ice-nucleation process.
Thermal hysteresis
AFPs create a difference between the melting point and freezing point (busting temperature of AFP bound ice crystal) known as thermal hysteresis. The addition of AFPs at the interface between solid ice and liquid water inhibits the thermodynamically favored growth of the ice crystal. Ice growth is kinetically inhibited by the AFPs covering the water-accessible surfaces of ice.
Thermal hysteresis is easily measured in the lab with a
nanolitre osmometer. Organisms differ in their values of thermal hysteresis. The maximum level of thermal hysteresis shown by fish AFP is approximately −3.5 °C (Sheikh Mahatabuddin et al., SciRep)(29.3 °F). In contrast, aquatic organisms are exposed only to −1 to −2 °C below freezing. During the extreme winter months, the
spruce budworm
''Choristoneura'' is a genus of moths in the family Tortricidae. Several species are serious pests of conifers, such as spruce and are known as spruce budworms.
Species
*'' Choristoneura adumbratanus'' (Walsingham, 1900)
*'' Choristoneura afri ...
resists freezing at temperatures approaching −30 °C.
The rate of cooling can influence the thermal hysteresis value of AFPs. Rapid cooling can substantially decrease the nonequilibrium freezing point, and hence the thermal hysteresis value. Consequently, organisms cannot necessarily adapt to their subzero environment if the temperature drops abruptly.
Freeze tolerance versus freeze avoidance
Species containing AFPs may be classified as
Freeze avoidant: These species are able to prevent their body fluids from freezing altogether. Generally, the AFP function may be overcome at extremely cold temperatures, leading to rapid ice growth and death.
Freeze tolerant: These species are able to survive body fluid freezing. Some freeze tolerant species are thought to use AFPs as cryoprotectants to prevent the damage of freezing, but not freezing altogether. The exact mechanism is still unknown. However, it is thought AFPs may inhibit recrystallization and stabilize cell membranes to prevent damage by ice.
They may work in conjunction with ice
nucleating proteins (INPs) to control the rate of ice propagation following freezing.
Diversity
There are many known
nonhomologous types of AFPs.
Fish AFPs
Antifreeze
glycoproteins
Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosy ...
or AFGPs are found in
Antarctic
The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...
notothenioid
Notothenioidei is one of 19 suborders of the order Perciformes. The group is found mainly in Antarctic and Subantarctic waters, with some species ranging north to southern Australia and southern South America. Notothenioids constitute approxi ...
s and
northern cod. They are 2.6-3.3 kD.
AFGPs evolved separately in notothenioids and northern cod. In notothenioids, the AFGP gene arose from an ancestral trypsinogen-like serine protease gene.
*Type I AFP is found in
winter flounder
The winter flounder (''Pseudopleuronectes americanus''), also known as the black back, is a right-eyed ("dextral") flatfish of the family Pleuronectidae. It is native to coastal waters of the western north Atlantic coast, from Labrador, Canada to ...
,
longhorn sculpin
The longhorn sculpin (''Myoxocephalus octodecemspinosus'') is a Northwest Atlantic species of sculpin in the fish family Cottidae. It is a predatory and scavenging fish that can feed on the remains of other organisms.
Appearance
The longhorn ...
and
shorthorn sculpin
''Myoxocephalus scorpius'', typically known as the shorthorn sculpin or bull-rout, is a species of fish in the family Cottidae. It is a demersal species of the Northern Atlantic and adjacent subarctic and Arctic seas. . It is the best documented AFP because it was the first to have its three-dimensional structure determined.
Type I AFP consists of a single, long, amphipathic alpha helix, about 3.3-4.5 kD in size. There are three faces to the 3D structure: the hydrophobic, hydrophilic, and Thr-Asx face.
**Type I-hyp AFP (where hyp stands for hyperactive) are found in several righteye flounders. It is approximately 32 kD (two 17 kD dimeric molecules). The protein was isolated from the blood plasma of winter flounder. It is considerably better at depressing freezing temperature than most fish AFPs.
The ability is partially derived from its many repeats of the Type I ice-binding site.
*Type II AFPs (e.g. ) are found in
sea raven
Sea ravens are a family, the ''Hemitripteridae'', of scorpaeniform fish. They are bottom-dwelling fish that feed on small invertebrates, found in the northwest Atlantic and north Pacific Oceans. They are covered in small spines (modified scales). ...
,
smelt
Smelt may refer to:
* Smelting, chemical process
* The common name of various fish:
** Smelt (fish), a family of small fish, Osmeridae
** Australian smelt in the family Retropinnidae and species ''Retropinna semoni''
** Big-scale sand smelt ''Ath ...
and
herring. They are cysteine-rich globular proteins containing five
disulfide bond
In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...
s.
Type II AFPs likely evolved from calcium dependent (c-type) lectins.
Sea ravens, smelt, and herring are quite divergent lineages of
teleost
Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...
. If the AFP gene were present in the most recent common ancestor of these lineages, it is peculiar that the gene is scattered throughout those lineages, present in some orders and absent in others. It has been suggested that lateral gene transfer could be attributed to this discrepancy, such that the smelt acquired the type II AFP gene from the herring.
[ ]
*Type III AFPs are found in Antarctic
eelpout
The eelpouts are the ray-finned fish family Zoarcidae. As the common name suggests, they are somewhat eel-like in appearance. All of the roughly 300 species are marine and mostly bottom-dwelling, some at great depths. Eelpouts are predominantly ...
. They exhibit similar overall hydrophobicity at ice binding surfaces to type I AFPs. They are approximately 6kD in size.
Type III AFPs likely evolved from a sialic acid synthase (SAS) gene present in Antarctic eelpout. Through a gene duplication event, this gene—which has been shown to exhibit some ice-binding activity of its own—evolved into an effective AFP gene by loss of the N-terminal part.
*Type IV AFPs () are found in longhorn sculpins. They are alpha helical proteins rich in glutamate and glutamine.
This protein is approximately 12KDa in size and consists of a 4-helix bundle.
Its only posttranslational modification is a
pyroglutamate
Pyroglutamic acid (also known as PCA, 5-oxoproline, pidolic acid) is a ubiquitous but little studied natural amino acid derivative in which the free amino group of glutamic acid or glutamine cyclizes to form a lactam. The names of pyroglutamic ...
residue, a cyclized
glutamine
Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...
residue at its
N-terminus
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...
.
Plant AFPs
The classification of AFPs became more complicated when antifreeze proteins from plants were discovered.
Plant AFPs are rather different from the other AFPs in the following aspects:
#They have much weaker thermal hysteresis activity when compared to other AFPs.
#Their physiological function is likely in inhibiting the recrystallization of ice rather than in preventing ice formation.
#Most of them are evolved
pathogenesis
Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...
-related proteins, sometimes retaining
antifungal properties.
Insect AFPs
There are a number of AFPs found in insects, including those from ''Dendroides'', ''Tenebrio'' and ''Rhagium'' beetles, spruce budworm and pale beauty moths, and midges (same order as flies). Insect AFPs share certain similarities, with most having higher activity (i.e. greater thermal hysteresis value, termed hyperactive) and a repetitive structure with a flat ice-binding surface. Those from the closely-related ''Tenebrio'' and ''Dendroides'' beetles are homologous and each 12–13 amino-acid repeat is stabilized by an internal disulfide bond. Isoforms have between 6 and 10 of these repeats that form a coil, or beta-solenoid. One side of the solenoid has a flat ice-binding surface that consists of a double row of threonine residues.
Other beetles (genus ''Rhagium'') have longer repeats without internal disulfide bonds that form a compressed beta-solenoid (beta sandwich) with four rows of threonine residus, and this AFP is structurally similar to that modelled for the non-homologous AFP from the pale beauty moth. In contrast, the AFP from the spruce budworm moth is a solenoid that superficially resembles the ''Tenebrio'' protein, with a similar ice-binding surface, but it has a triangular cross-section, with longer repeats that lack the internal disulfide bonds. The AFP from midges is structurally similar to those from ''Tenebrio'' and ''Dendroides'', but the disulfide-braced beta-solenoid is formed from shorter 10 amino-acids repeats, and instead of threonine, the ice-binding surface consists of a single row of tyrosine residues. Springtails (Collembola) are not insects, but like insects, they are arthropods with six legs. A species found in Canada, which is often called a "snow flea", produces hyperactive AFPs.
Although they are also repetitive and have a flat ice-binding surface, the similarity ends there. Around 50% of the residues are glycine (Gly), with repeats of Gly-Gly- X or Gly-X-X, where X is any amino acid. Each 3-amino-acid repeat forms one turn of a polyproline type II helix. The helices then fold together, to form a bundle that is two helices thick, with an ice-binding face dominated by small hydrophobic residues like alanine, rather than threonine. Other insects, such as an Alaskan beetle, produce hyperactive antifreezes that are even less similar, as they are polymers of sugars (xylomannan) rather than polymers of amino acids (proteins).
Taken together, this suggests that most of the AFPs and antifreezes arose after the lineages that gave rise to these various insects diverged. The similarities they do share are the result of convergent evolution.
Sea ice organism AFPs
Many microorganisms living in
sea ice possess AFPs that belong to a single family. The
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s ''Fragilariopsis cylindrus'' and ''F. curta'' play a key role in polar sea ice communities, dominating the assemblages of both platelet layer and within pack ice. AFPs are widespread in these species, and the presence of AFP
genes
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
as a multigene family indicates the importance of this group for the genus ''Fragilariopsis''.
AFPs identified in ''F. cylindrus'' belong to an AFP family which is represented in different taxa and can be found in other organisms related to sea ice (''
Colwellia'' spp., ''Navicula glaciei'', ''Chaetoceros neogracile'' and ''Stephos longipes and Leucosporidium antarcticum'')
and Antarctic inland ice bacteria (
Flavobacteriaceae
The family Flavobacteriaceae is composed of environmental bacteria. Most species are aerobic, while some are microaerobic to anaerobic; for example ''Capnocytophaga'' and '' Coenonia''.
Genera
The family ''Flavobacteriaceae'' comprises the foll ...
),
as well as in cold-tolerant fungi (''
Typhula ishikariensis
''Typhula ishikariensis'' is, along with ''Typhula incarnata'', the causal agent of grey snow mould (also called speckled snow mould or ''Typhula'' blight), an obligately parasitic plant pathogen that can destroy turfgrass when covered for a lo ...
'', ''
Lentinula edodes
The shiitake (alternate form shitake) (; ''Lentinula edodes'') is an edible mushroom native to East Asia, which is now cultivated and consumed around the globe. It is considered a medicinal mushroom in some forms of traditional medicine.
Ta ...
'' and ''
Flammulina populicola'').
Several structures for sea ice AFPs have been solved. This family of proteins fold into a
beta helix
A beta helix is a tandem protein repeat structure formed by the association of parallel beta strands in a helical pattern with either two or three faces. The beta helix is a type of solenoid protein domain. The structure is stabilized by inter- ...
that form a flat ice-binding surface. Unlike the other AFPs, there is not a singular sequence motif for the ice-binding site.
AFP found from the metagenome of the
ciliate
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a differen ...
''Euplotes focardii'' and psychrophilic bacteria has an efficient ice re-crystallization inhibition ability.
1 μM of ''Euplotes focardii'' consortium ice-binding protein (''Efc''IBP) is enough for the total inhibition of ice re-crystallization in –7.4 °C temperature. This ice-recrystallization inhibition ability helps bacteria to tolerate ice rather than preventing the formation of ice. ''Efc''IBP produces also thermal hysteresis gap, but this ability is not as efficient as the ice-recrystallization inhibition ability. ''Efc''IBP helps to protect both purified proteins and whole bacterial cells in freezing temperatures.
Green fluorescent protein is functional after several cycles of freezing and melting when incubated with ''Efc''IBP. ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' survives longer periods in 0 °C temperature when the ''efcIBP'' gene was inserted to ''E. coli'' genome.
''Efc''IBP has a typical AFP structure consisting of multiple
beta-sheet
The beta sheet, (β-sheet) (also β-pleated sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a g ...
s and an
alpha-helix. Also, all the ice-binding polar residues are at the same site of the protein.
Evolution
The remarkable diversity and distribution of AFPs suggest the different types evolved recently in response to sea level
glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
occurring 1–2 million years ago in the Northern hemisphere and 10-30 million years ago in Antarctica. Data collected from deep sea ocean drilling has revealed that the development of the Antarctic Circumpolar Current was formed over 30 million years ago.
The cooling of Antarctic imposed from this current caused a mass extinction of teleost species that were unable to withstand freezing temperatures.
Notothenioids species with the antifreeze gylcoprotein were able to survive the glaciation event and diversify into new niches.
This independent development of similar adaptations is referred to as
convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
.
Evidence for convergent evolution in Northern cod (
Gadidae
The Gadidae are a family of marine fish, included in the order Gadiformes, known as the cods, codfishes, or true cods. It contains several commercially important fishes, including the cod, haddock, whiting, and pollock.
Most gadid species ...
) and Notothenioids is supported by the findings of different spacer sequences and different organization of introns and exons as well as unmatching AFGP tripeptide sequences, which emerged from duplications of short ancestral sequences which were differently permuted (for the same tripeptide) by each group. These groups diverged approximately 7-15 million years ago. Shortly after (5-15 mya), the AFGP gene evolved from an ancestral pancreatic trypsinogen gene in Notothenioids. AFGP and trypsinogen genes split via a sequence divergence - an adaptation which occurred alongside the cooling and eventual freezing of the Antarctic Ocean. The evolution of the AFGP gene in Northern cod occurred more recently (~3.2 mya) and emerged from a noncoding sequence via tandem duplications in a Thr-Ala-Ala unit. Antarctic notothenioid fish and artic cod, Boreogadus saida, are part of two distinct orders and have very similar antifreeze glycoproteins.
Although the two fish orders have similar antifreeze proteins, cod species contain arginine in AFG, while Antarctic notothenioid do not.
[ The role of arginine as an enhancer has been investigated in Dendroides canadensis antifreeze protein (DAFP-1) by observing the effect of a chemical modification using 1-2 cyclohexanedione.] Previous research has found various enhancers of this bettles' antifreeze protein including a thaumatin-like protein and polycarboxylates. Modifications of DAFP-1 with the arginine specific reagent resulted in the partial and complete loss of thermal hysteresis in DAFP-1, indicating that arginine plays a crucial role in enhancing its ability. Different enhancer molecules of DAFP-1 have distinct thermal hysteresis activity. Amornwittawat et al. 2008 found that the number of carboxylate groups in a molecules influence the enhancing ability of DAFP-1. Optimum activity in TH is correlated with high concentration of enhancer molecules. Li et al. 1998 investigated the effects of pH and solute on thermal hysteresis in Antifreeze proteins from Dendrioides canadensis. TH activity of DAFP-4 was not affected by pH unless the there was a low solute concentration (pH 1) in which TH decreased. The effect of five solutes; succinate, citrate, malate, malonate, and acetate, on TH activity was reported. Among the five solutes, citrate was shown to have the greatest enhancing effect.
This is an example of a proto-ORF model, a rare occurrence where new genes pre exist as a formed open reading frame before the existence of the regulatory element needed to activate them.
In fishes, horizontal gene transfer is responsible for the presence of Type II AFP proteins in some groups without a recently shared phylogeny. In Herring and smelt, up to 98% of introns for this gene are shared; the method of transfer is assumed to occur during mating via sperm cells exposed to foreign DNA. The direction of transfer is known to be from herring to smelt as herring have 8 times the copies of AFP gene as smelt (1) and the segments of the gene in smelt house transposable element
A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Transp ...
s which are otherwise characteristic of and common in herring but not found in other fishes.
There are two reasons why many types of AFPs are able to carry out the same function despite their diversity:
# Although ice is uniformly composed of water molecules, it has many different surfaces exposed for binding. Different types of AFPs may interact with different surfaces.
# Although the five types of AFPs differ in their primary structure of amino acids, when each folds into a functioning protein they may share similarities in their three-dimensional or tertiary structure
Protein tertiary structure is the three dimensional shape of a protein. The tertiary structure will have a single polypeptide chain "backbone" with one or more protein secondary structures, the protein domains. Amino acid side chains may i ...
that facilitates the same interactions with ice.
Antifreeze glycoprotein activity has been observed across several ray-finned species including eelpouts, sculpins, and cod species. Fish species that possess the antifreeze glycoprotein express different levels of protein activity. Polar cod (''Boreogadus saida)'' exhibit similar protein activity and properties to the Antarctic species, ''T. borchgrevinki''.[ Both species have higher protein activity than saffron cod (''Eleginus gracilis'').][ Ice antifreeze proteins have been reported in diatom species to help decrease the freezing point of organism's proteins.] Bayer-Giraldi et al. 2010 found 30 species from distinct taxa with homologues of ice antifreeze proteins. The diversity is consistent with previous research that has observed the presence of these genes in crustaceans, insects, bacteria, and fungi. Horizontal gene transfer is responsible for the presence of ice antifreeze proteins in two sea diatom species, F. cylindrus and F. curta.
Mechanisms of action
AFPs are thought to inhibit growth by an adsorption
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which ...
–inhibition mechanism. They adsorb to nonbasal plane
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns t ...
s of ice, inhibiting thermodynamically-favored ice growth. The presence of a flat, rigid surface in some AFPs seems to facilitate its interaction with ice via Van der Waals force
In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and th ...
surface complementarity.
Binding to ice
Normally, ice crystals grown in solution only exhibit the basal (0001) and prism faces (1010), and appear as round and flat discs. However, it appears the presence of AFPs exposes other faces. It now appears the ice surface 2021 is the preferred binding surface, at least for AFP type I. Through studies on type I AFP, ice and AFP were initially thought to interact through hydrogen bonding (Raymond and DeVries, 1977). However, when parts of the protein thought to facilitate this hydrogen bonding were mutated, the hypothesized decrease in antifreeze activity was not observed. Recent data suggest hydrophobic interactions could be the main contributor. It is difficult to discern the exact mechanism of binding because of the complex water-ice interface. Currently, attempts to uncover the precise mechanism are being made through use of molecular modelling
Molecular modelling encompasses all methods, theoretical and computational, used to model or mimic the behaviour of molecules. The methods are used in the fields of computational chemistry, drug design, computational biology and materials sci ...
programs (molecular dynamics
Molecular dynamics (MD) is a computer simulation method for analyzing the physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamic "evolution" of the ...
or the Monte Carlo method
Monte Carlo methods, or Monte Carlo experiments, are a broad class of computational algorithms that rely on repeated random sampling to obtain numerical results. The underlying concept is to use randomness to solve problems that might be determi ...
).
Binding mechanism and antifreeze function
According to the structure and function study on the antifreeze protein from ''Pseudopleuronectes americanus
The winter flounder (''Pseudopleuronectes americanus''), also known as the black back, is a right-eyed ("dextral") flatfish of the family Pleuronectidae. It is native to coastal waters of the western north Atlantic coast, from Labrador, Canada to ...
'', the antifreeze mechanism of the type-I AFP molecule was shown to be due to the binding to an ice nucleation structure in a zipper-like fashion through hydrogen bonding of the hydroxyl groups of its four Thr residues to the oxygens along the