Cterminal

Cterminal, commonly written as C-terminus or C terminal, is a term used in biochemistry and molecular biology to denote the end of a polypeptide chain that carries the free carboxyl group. In standard notation, protein and peptide sequences are read from the N-terminus to the C-terminus, with the N-terminus bearing the amino group and the C-terminus bearing the carboxyl group. The C-terminus can be essential for protein function, stability, localization, and interactions, and it may be subject to post-translational modifications such as amidation or proteolytic processing that reveal or alter the terminal sequence.

C-terminal regions often contain motifs or domains critical for protein activity or for mediating interactions with other molecules. They can influence folding, subcellular targeting, and degradation. Some proteins have explicit C-terminal targeting signals that direct cellular transport; for example, the peroxisomal targeting signal type 1 (PTS1) is a short tripeptide sequence ending at the extreme C-terminus. C-terminal tails also participate in regulatory processes, including signaling and the formation of multi-protein complexes. Proteolytic processing can generate mature proteins by producing new C-termini, a common mechanism in the maturation of hormones and enzymes.

C-terminal tagging is a widely used technique in research, where a tag or a fluorescent protein is fused to the C-terminus to aid detection, purification, or localization studies. Terminomics is a field of proteomics focused on identifying and quantifying protein C-termini to study proteolysis, maturation, and protein turnover on a large scale. The concept of the C-terminus is foundational in understanding protein structure and function alongside the N-terminus.