formylmetionin

Formylmethionine, or N-formylmethionine (fMet), is the N-formyl derivative of the amino acid methionine. It is used as the initiating amino acid for protein synthesis in most bacteria and in the organelles of eukaryotic cells with bacterial ancestry, such as mitochondria and chloroplasts.

Chemically, the amino group of methionine is modified with a formyl group (CHO) to give N-formylmethionine. The formyl group is added to the amino nitrogen by the enzyme methionyl-tRNA formyltransferase, using N10-formyltetrahydrofolate as the formyl donor. The charged initiator tRNA, tRNAfMet, then recognizes AUG start codons to initiate translation.

Post-translational processing typically removes the formyl group by peptide deformylase, and, in many cases, the initiator methionine is removed by methionine aminopeptidase depending on the protein and its N-terminal residue.

In contrast, cytosolic protein synthesis in most eukaryotes uses unformylated methionine for initiation. The bacterial origin of the organelles explains the conserved use of formylated initiator tRNA in mitochondria and chloroplasts.

Formylmethionine is also relevant in immunology as a source of N-formylated peptides, which can act as chemoattractants via formyl peptide receptors and help recruit immune cells to sites of infection.