Carboxy terminus

Carboxy Terminus

The carboxy terminus, also known as the C-terminus, is the end of an amino acid chain, or polypeptide, that terminates in a free carboxyl group (-COOH). This is in contrast to the amino terminus (N-terminus), which is the start of the polypeptide chain, terminating in a free amino group (-NH2). The C-terminus is an important structural and functional feature of proteins and peptides.

Structure

In a polypeptide chain, amino acids are linked together by peptide bonds, which are formed between the carboxyl group of one amino acid and the amino group of the next. The sequence of amino acids in a protein is written from the N-terminus to the C-terminus, reflecting the direction of protein synthesis by the ribosome.

The C-terminus is characterized by the presence of a free carboxyl group, which can participate in various chemical reactions. This terminal carboxyl group can be modified post-translationally, affecting the protein's function, localization, and stability.

Function

The C-terminus plays a crucial role in the function of proteins. It can be involved in:

• Protein stability: The C-terminus can influence the stability of the protein structure.
• Protein-protein interactions: Many proteins interact with other proteins through their C-terminal regions.
• Subcellular localization: Signals for targeting proteins to specific cellular compartments can be located at the C-terminus.
• Post-translational modifications: The C-terminus can be modified by the addition of various chemical groups, such as phosphorylation, acetylation, or ubiquitination, which can regulate protein activity and degradation.

Post-Translational Modifications

The C-terminus is a common site for post-translational modifications, which can alter the function and fate of the protein. Some common modifications include:

• Amidation: The conversion of the terminal carboxyl group to an amide group, which can affect the protein's charge and stability.
• Lipidation: The addition of lipid groups, which can anchor proteins to membranes.
• Glycosylation: The attachment of sugar moieties, which can affect protein folding and stability.

Importance in Research

Understanding the role of the C-terminus in protein function is crucial for biochemistry and molecular biology. It is often a focus in studies of protein structure-function relationships, protein engineering, and drug design.

Also see

• Amino terminus
• Protein structure
• Post-translational modification
• Peptide bond
• Protein synthesis

This diagram (which is interactive) of protein structure uses PCNA as an example. (PDB: 1AXC​)