R18, also known as R18 peptide is an antagonist of 14.3.3 proteins, a family of conserved regulatory molecules that have the ability to bind a multitude of functionally diverse signaling proteins, with a KD of approximately 80 nM. R18 competitively inhibits 14.3.3 ligand interactions without requiring phosphorylation and can block the ability of 14.3.3 to bind to target proteins such as Raf-1, Bad, ASK1 and exoenzyme S.
