The “inverted” protein

  • Thread starter Eagle9
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Good day! :oldsmile:

Imagine the mRNA with some nucleotide sequence that (after translation) will give us such polypeptide chain:

L-Alanine (first, in the beginning of translation) - L-Arginine - L-Asparagine - L-Aspartic acid - L-Cysteine - L-Glutamic acid - L-Glutamine - Glycine (last, in the end of translation)

Such (or imagine longer one, its length is not crucial in my question) chain will fold after translation and we will get some certain protein.

Now imagine the polypeptide chain with inverted sequence, that is first we get (from ribosome) Glycine, then L-Glutamine and so on:

Glycine - L-Glutamine - L-Glutamic acid - L-Cysteine - L-Aspartic acid - L-Asparagine - L-Arginine - L-Alanine

This chain will also fold, but what we will receive? The same protein?

If the folding process depends only on polypeptide contents (number of amino acids, their chemical properties and sequence) then this “invertness” would not matter and we should get two identical proteins, right?

But if the folding process (and final product) begins as soon as polypeptide chain (more precisely its part) exits ribosome then we will have different amino acid sequencing to fold, in first case we have L-Alanine - L-Arginine - L-Asparagine…………… and in second case: Glycine - L-Glutamine - L-Glutamic acid…………….

So, what do you think? :oldeyes:
 

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  • #2
BillTre
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If the folding process depends only on polypeptide contents (number of amino acids, their chemical properties and sequence) then this “invertedness” would not matter and we should get two identical proteins, right?
By the sequence, the your protein would still be different because to two ends of the proteins would be different (COOH at one end vs. NH2 at the other). The amino acids with the different terminations would change when the direction of synthesis is changed.
To make them the same, the protein sequence would have to be a palindrome. The both ends would match up with the original.

If only the ends were palindromic and the middle was not, there is the risk that the protein being synthesized would fold up (gong from a string of amino acids to the final 3D structure of the protein) in a different manner (based on the different sequence of amino acids being inserted into the developing protein as it comes out of the ribosome. The folding a protein undergoes can be sequence specific for local regions with different amino acid sequences.
 
  • #3
Ygggdrasil
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A Bill noted, polypeptide sequences have a polarity to then and one end is not equivalent to the other.

In some cases, it is possible to re-arrange a protein sequence through circular permutation and retain the same overall structure of the protein: https://en.wikipedia.org/wiki/Circular_permutation_in_proteins
 
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