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Why do organisms found at low temperatures have membrane proteins with a higher percentage of alpha helices compare to beta sheets?

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    $\begingroup$ This is an interesting question that I've not really come across before. Is there a citation for this claim? I'd be interested to read more. $\endgroup$ – James Apr 17 '17 at 2:27
  • $\begingroup$ @James Porins are beta barrel but yeah many membrane proteins are alpha-helical, though I don't have an exact number. $\endgroup$ – WYSIWYG Apr 17 '17 at 5:57
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    $\begingroup$ @WYSIWYG I once looked at the difference between the two and TMHs are far more common (~13k proteins 90% redundant with a TMH in humans, and only around ~1k TM beta sheet containing proteins in Swissprot without selecting a specific taxonomy or redundancy ). What I have not come across is something saying that the ratio shifts in organisms that are at lower temperatures.The annotation of beta sheet TMDs is nowhere near as high quality as TMHs, so I assumed that nobody had looked into this. $\endgroup$ – James Apr 17 '17 at 7:30
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The reason could be the greater motility of the alpha helix, compared with the more rigid beta sheet. This allows the enzyme to remain functional at low temperature. The proteins of such organisms tend also to have less hydrophobic regions and covalent bonds.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1692995/pdf/12171655.pdf Molecular basis of cold adaptation Salvino D’Amico, Paule Claverie, Tony Collins, Daphne´ Georlette, Emmanuelle Gratia, Anne Hoyoux, Marie-Alice Meuwis, Georges Feller and Charles Gerday*

This doesn't refer to alpha helix explicitly, however alpha helix are known to allow more flexibility than beta sheets, so it's reasonable to argue that the increase in alpha helix could be one of several strategies used to obtain more flexible enzymes, as well as other means cited in the paper.

This point is also made by Brock-Biology of microorganisms(2015) pag.161

Several cold-active enzymes whose structure is known show a greater content of α-helix and lesser content of β-sheet secondary structure ( Section 4.14) than do enzymes that show little or no activity in the cold. Because β-sheet secondary structures tend to be more rigid than α-helices, the greater α-helix content of cold-active enzymes allows these proteins greater flexibility for catalyzing their reactions at cold temperatures.

However unfortunately no reference is provided about this claim.

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    $\begingroup$ This is a great idea for a comment, but it's not an answer. It would be if it had sources, or calculations etc. $\endgroup$ – James Apr 17 '17 at 7:20

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