The N-terminus (also known as amino-terminus , NH 2 -terminus , N-terminal end or amine terminus ) is the beginning of a protein or polypeptide referring to the free amine group (NH 2 ) located at the end of a polypeptide. . Within a peptide, the amine group is bonded to another carboxylic group in a protein to form a chain, but since the protein’s end amino acid is attached only at the carboxy-end, the remaining free amine group is referred to as the N- goes. According to the terminus convention, peptide sequences are separated from the N-terminus.The C-terminus is written from left to right ( in the LTR writing system ). [1] It links translation direction to text direction (because when a protein is translated from messenger RNA , it is made from the N-terminus to the C-terminus – amino acids are added at the carboxyl end).
chemistry
Each amino acid contains an amine group and a carboxylic group . Amino acids are joined to each other by peptide bonds that are formed through a dehydration reaction that links the carboxyl group of one amino acid to the amine group of the next in a head-to-tail manner to form a polypeptide chain . The chain has two ends – an amine group, the N-terminus, and an unbound carboxyl group, the C-terminus . [2]
When a protein is translated from messenger RNA , it is made from the N-terminus to the C-terminus. The amino end of an amino acid ( on a charged tRNA ) binds to the carboxyl end of the growing chain during the elongation phase of translation . Since the start codon of the genetic code codes for the amino acid methionine , most protein sequences begin with methionine (or, in bacteria, mitochondria and chloroplasts , the modified version N -formylmethionine , fmet). However, some proteins have been shown to be posttranslational .are modified, for example, by cleavage from a protein precursor, and therefore may have different amino acids at their N-terminus.
Celebration
N-terminal targeting signal
The N-terminus is the first part of the protein that exits the ribosome during protein biosynthesis. It often contains signal peptide sequences, “intracellular postal codes” that direct the protein to the appropriate organelle. The signal peptide is usually removed at the destination by a signal peptidase. The N-terminal amino acid of a protein is an important determinant of its half-life (likely to be degraded). This is called the n-end rule.
signal peptide
The N-terminal signal peptide is recognized by the signal recognition particle (SRP) and the resulting protein is targeted to the secretory pathway. In cells, these proteins are somehow synthesized by the reticulum. In prokaryotic cells, proteins are exported across the cell membrane. In chloroplasts, signal peptides target proteins to thylakoids.
mitochondrial targeting peptide
The N-terminal mitochondrial targeting peptide (MTTP) allows the protein to be imported into the mitochondrion.
chloroplast targeting peptide
The N-terminal chloroplast targeting peptide (CPTP) allows the protein to be imported into the chloroplast.
N-terminal modification
The protein N-termini can be co- or posttranslationally modified. Modifications include removal of the initiator methionine (imet) by aminopeptidases, the attachment of small chemical groups such as acetyl, propionyl and methyl, and the addition of membrane anchors, such as palmitoyl and myristoyl groups [3]
N-terminal acetylation
N-terminal acetylation is a form of protein modification that can occur in both prokaryotes and eukaryotes. It has been suggested that N-terminal acetylation may prevent a protein from following a secretory pathway. [4]
n-myristoylation
The N-terminus can be modified by the addition of a myristoyl anchor. Proteins modified in this way have a consensus signal at their N-terminus as a modification signal.
N-acylation
The N-terminus can also be modified to form N-acylated proteins by addition of fatty acid anchors. The most common form of such modification is the addition of a palmitoyl group.
