Cterminaalne

C-terminaalne, or C-terminus, refers to the end of a protein or polypeptide that carries the free carboxyl group. It is opposite the N-terminus, which bears the amino group. Proteins are synthesized from the N-terminus to the C-terminus, and the C-terminal region often influences function, stability, and interactions, either on its own or through post-translational modifications.

The C-terminus can contain signals that determine cellular localization. For example, the peroxisomal targeting signal type 1 (PTS1) is a short C-terminal tripeptide, commonly Ser-Lys-Leu, recognized by cytosolic receptors to import the protein into peroxisomes. C-terminal motifs also participate in protein–protein interactions, such as PDZ-binding motifs that reside at the extreme C-terminus of many receptors and scaffold proteins, binding to PDZ domains.

Post-translational modifications and processing often affect the C-terminus. C-terminal amidation is a common modification in neuropeptides and reflex peptides, where a terminal glycine residue serves as an amide donor. Proteolytic clipping at the C-terminus can activate or deactivate signaling peptides and prohormones. In many proteins, the C-terminal tail contributes to stability, folding, or the formation of transient interactions, and in some cases, it forms a structured domain or an unstructured regulatory tail.

In research and bioinformatics, the C-terminus is used to classify protein families, identify functional motifs, and predict localization. Its variability across proteins reflects a balance between essential core structure and adaptable regulatory roles.