The removal of methionine from the polypeptide chain in protein synthesis

Introduction:
In protein synthesis, the first amino acid incorporated into the growing polypeptide chain is usually methionine. This occurs during the process of translation, where the information encoded in mRNA is used to synthesize a specific protein. However, in some cases, methionine may not be required in the final functional protein. In such instances, methionine needs to be removed from the polypeptide chain. This removal is carried out by a specific enzyme known as amino peptidase.

The role of amino peptidase enzyme:
1. Amino peptidase enzyme is responsible for the removal of the N-terminal amino acid from the polypeptide chain.
2. It specifically targets the methionine residue and cleaves it off from the chain.
3. This enzymatic cleavage occurs only if the second amino acid in the chain is smaller than methionine, as the enzyme has a preference for smaller amino acids.

Process of methionine removal:
1. Initiation: During translation, the ribosome binds to the mRNA molecule and scans for the start codon, which usually codes for methionine.
2. Incorporation: The initiator tRNA, which carries methionine, binds to the start codon, and methionine is incorporated into the growing polypeptide chain.
3. Translocation: The ribosome moves along the mRNA, adding more amino acids to the growing chain.
4. Recognition: Once the ribosome reaches a point where methionine is no longer required, the amino peptidase enzyme recognizes the presence of a smaller amino acid at the second position.
5. Cleavage: The amino peptidase enzyme cleaves off the methionine from the polypeptide chain, leaving the next amino acid to occupy the first position.
6. Continuation: The ribosome continues the process of translation, adding more amino acids to the chain.

Conclusion:
In protein synthesis, the removal of methionine from the polypeptide chain is carried out by the amino peptidase enzyme. This enzyme recognizes the presence of a smaller amino acid at the second position and cleaves off methionine. This allows the growing polypeptide chain to continue its synthesis without the presence of methionine, if it is not required in the final functional protein.

3) Amino peptidase enzyme