A
tetrapeptide is a
peptide, classified as an
oligopeptide, since it only consists of four
amino acids joined by
peptide bonds. Many tetrapeptides are
pharmacologically active, often showing affinity and specificity for a variety of receptors in protein-protein signaling. Present in nature are both linear and
cyclic tetrapeptides, tetrapeptides may be
cyclized by a fourth peptide bond or other
covalent bonds.