aloitusmetioniini

Aloitusmetioniini, also known as N-formylmethionine (fMet) in prokaryotes, is a modified amino acid that plays a crucial role in initiating protein synthesis in bacteria and other prokaryotic organisms. Unlike the methionine that is incorporated into proteins internally, aloitusmetioniini is exclusively used as the very first amino acid of every newly synthesized polypeptide chain. Its formylation, the addition of a formyl group to the alpha-amino group of methionine, is catalyzed by an enzyme called methionine formyltransferase. This modification is essential for efficient binding of the initiator tRNA (tRNAfMet) to the ribosomal P-site, a critical step in the initiation phase of translation.

Following initiation, the formyl group is typically removed from the N-terminus of the nascent polypeptide by a deformylase enzyme. In some cases, the entire aloitusmetioniini residue is also removed by methionine aminopeptidases. The presence of aloitusmetioniini is a hallmark of prokaryotic protein synthesis and is absent in eukaryotic protein synthesis, where regular methionine initiates translation. This difference has been exploited in the development of antibiotics. Certain antibiotics target bacterial protein synthesis by interfering with the processing or function of aloitusmetioniini, thereby selectively inhibiting bacterial growth without significantly affecting host eukaryotic cells.