N-terminus

N-terminus or amino-terminus is the start of a protein or polypeptide referring to the free amino acid group (-NH2) located at the end of a polypeptide chain. Proteins are synthesized from the N-terminus to the C-terminus, following the direction from the amino acid with the free amino group (the N-terminus) to the amino acid with the free carboxyl group (the C-terminus) in ribosomes. This directionality is crucial for the structure and function of proteins.

Structure and Function

The N-terminus is characterized by its amino acid sequence, which can significantly influence the protein's stability, localization, and function. For example, the N-terminal signal peptide is a short amino acid sequence that directs the protein to its correct location within the cell, such as the endoplasmic reticulum or the mitochondria. Additionally, modifications of the N-terminus, such as acetylation, can affect protein activity and interactions.

Genetic Encoding

The genetic code determines the sequence of amino acids, including the N-terminus, during protein synthesis. The mRNA template, which is transcribed from DNA, contains codons that specify which amino acids will be added to the growing polypeptide chain. The process begins with the start codon (AUG), which codes for methionine in eukaryotes or a modified methionine in prokaryotes, marking the N-terminus of the synthesized protein.

Post-translational Modifications

After synthesis, proteins can undergo various post-translational modifications (PTMs) that can occur at the N-terminus. These modifications can include the removal of the initial methionine, acetylation, and the addition of functional groups or other proteins. These changes can regulate protein function, stability, and interactions with other molecules.

Importance in Research and Medicine

Understanding the N-terminus of proteins is crucial in biochemistry, molecular biology, and medicine. It plays a significant role in the development of drugs and therapeutic agents, as modifications at the N-terminus can alter protein function. Additionally, the analysis of N-terminal sequences can aid in the identification and characterization of proteins.

See Also

• C-terminus
• Protein synthesis
• Post-translational modification
• Signal peptide