N terminus

A tetrapeptide (such as Val - Gly - Ser - Ala ) with
green marked N -terminal α-amino acid (in the example: L -Valin ) and blue- marked C -terminal α-amino acid (in the example: L -alanine ).

As N -terminus or amino-terminus is that the end of a protein or polypeptide refers to that in eukaryotes and archaea an amino acid having a free amino group (NH ₂ has). In bacteria, however , newly synthesized proteins begin with N -formylmethionine (fMet), in which the amino group is formylated .

properties

The ribosome starts protein synthesis at the N terminus with a methionine as the first amino acid of the new protein to be formed. The N terminus initially remains unmodified, while the carboxy group of the amino acid is covalently linked to the NH ₂ group of the next amino acid via a peptide bond .

The free amino group gives the name to the N terminus, but can be modified later during and after translation. In eukaryotes, for example, the N terminus is often acetylated in the course of a post-translational modification by an acetyltransferase , and sometimes also myristylated or palmitylated . More specific N -terminal modifications are, for example, the splitting off of parts by proteolysis or the subsequent addition of amino acids, as in arginylation . Proteolysis of a protein can turn its C -terminal fragments into new proteins whose N -terminal amino acid is no longer methionine. Methionine aminopeptidases can split off the methionine at the N terminus. The N -terminal amino acid can accelerate the proteolytic degradation of a protein, which is described by the N -end rule .

Shortly after the N terminus there is often a signal sequence , e.g. B. those for secretory or mitochondrial proteins in all eukaryotes and those for plastid proteins of plants.

The opposite end of the molecule of any peptide is called the carboxy terminus ( C -terminus for short).

literature

• Hans Beyer , Wolfgang Walter : Textbook of organic chemistry S. Hirzel Verlag, Stuttgart, 19th edition, ISBN 3-7776-0356-2 .
• WC Chan, PD White: Fmoc Solid Phase Peptide Synthesis. Reprint 2004, Oxford University Press, ISBN 0-19-963724-5 .

Individual evidence

1. ↑ Michael T. Madigan, John M. Martinko: Brock Mikrobiologie 11th edition, Pearson Studium, Munich 2006, ISBN 3-8273-7187-2 .
2. ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, pp. 1031-1033.