User:User53184/Antifreeze protein

Article body
"The remarkable diversity and distribution of AFPs suggest the different types evolved recently in response to sea level glaciation 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 Antarctica imposed from this current caused a mass extinction of teleost species that were unable to withstand freezing temperatures .Notothenioid species with the antifreeze glycoprotein were able to survive the glaciation event and diversify into new niches . This independent development of similar adaptations is referred to as convergent evolution." <-- split this quote in half?

Evidence for convergent evolution in Northern cod (Gadidae) 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 the artic cod, Boreogadus saida, are part of two distinct orders and have very similar antifreeze glycoproteins. Although the two fish orders have similar AFG, cod species contain arginine in AFG, while Antarctic notothenioids do not .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.

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 had found various enhancers of this species 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 is plays a crucial role in enhancing its ability.

Another way these genes can emerge is through Horizontal gene transfer. HGT is responsible for the presence of Type II AFP proteins in 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; herring have 8 times the copies of AFP gene as smelt (1) and the segments of the gene in smelt house transposable elements 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:

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.
 * 1) 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.
 * 2) 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 that facilitates the same interactions with ice."