How Do Antifreeze Proteins Help Antarctic Fish Survive the Cold?

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Discussion Overview

The discussion centers on the role of antifreeze proteins in Antarctic notothenioid fish and their mechanism for preventing freezing in icy environments. Participants explore the nature of these proteins, their interactions with ice, and the implications of terminology used in the context of molecular interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that antifreeze proteins bind to ice crystals to inhibit their growth.
  • Another participant proposes that water might act as a ligand, questioning the idea of a protein functioning without molecular interaction.
  • A later reply reinforces the idea that the protein binds to tiny ice crystals, preventing their growth and describes the mechanism as kinetically depressing the temperature at which ice forms.
  • Some participants express confusion over the use of the term "ligand," arguing that it typically refers to molecules binding to receptors, and question whether water fits this definition.
  • There is a discussion about the functional exposure of long chain amino acids in the protein, suggesting that they interact with ice crystals without necessarily causing a reaction.

Areas of Agreement / Disagreement

Participants express differing views on the terminology used, particularly regarding the concept of a ligand and its application in this context. There is no consensus on the precise nature of the interactions between antifreeze proteins and ice.

Contextual Notes

The discussion highlights potential limitations in the definitions of terms like "ligand" and the assumptions underlying the proposed mechanisms of action for antifreeze proteins.

Who May Find This Useful

This discussion may be of interest to those studying evolutionary biology, protein chemistry, or the adaptations of organisms to extreme environments.

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Anyone know the answer to this ridiculous problem

Antarctic notothenioid fish avoid freezing in their perpetually icy environment because of an antifreeze protein that circulates in their blood. This evolutionary adaptation has allowed these fish to rise to dominance in the freezing southern ocean. It is said that all proteins function by binding to other molecules. To what ligand do you suppose antifreeze proteins bind to keep the fish from freezing.? Or do you think this might be an example of a protein that functions in the absence of any molecular interaction?

Anyone have any suggestions, thanks
 
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I would have to guess... the ligand would be ice crystals to stop them from growing.
 
If there is a ligand, then I suppose it would be water. Some chemical functioning in the absence of any interaction sounds kinda fishy to me... Pun intended. But biology isn't my thing.
 
Last edited:
Jikx said:
I would have to guess... the ligand would be ice crystals to stop them from growing.

You are right. The protein binds to tiny ice crystal and prevent the growth of these crystals.

But in more technical terms

These compounds allow the fish to survive in subzero ice-laden polar oceans by kinetically depressing the temperature at which ice grows in a noncolligative manner.
http://www.ncbi.nlm.nih.gov/entrez/...ve&db=pubmed&dopt=Abstract&list_uids=12653993

More info
http://www.ncbi.nlm.nih.gov/entrez/...rm=Antarctic+Notothenioids+antifreeze+protein
 
It seems the question has already been answered. The choice of the word "ligand" seems odd in this context. I usually think of ligand as a molecule binding to a receptor, not just any molecular interaction. I wouldn't consider water to be a "ligand" in the true sense of the word.
 
Moonbear said:
It seems the question has already been answered. The choice of the word "ligand" seems odd in this context. I usually think of ligand as a molecule binding to a receptor, not just any molecular interaction. I wouldn't consider water to be a "ligand" in the true sense of the word.
I agree, in most cases the ligand elicits some sort of reaction in the protein it is binding to, i.e., conformational change, translocation, channel activation, etc. In this case it appears that active groups, the long chain amino acids are functionally exposed prior to exposure to ice and ready to interact with the forming edges of ice crystals, so it's not necessarily reacting but simply inhibiting.
 

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