In the active sites of serine and cysteine proteases, the eponymous residue is usually paired with a proton-withdrawing group to promote nucleophilic attack on the peptide bond.

Enzymes that catalyse the hydrolytic cleavage of peptide bonds are called proteases. Proteases fall into four main mechanistic classes: serine, cysteine, aspartyl and metalloproteases.

Certain types of peptides and microproteins for drug discovery research can be made more efficiently and quickly using a reaction solvent that helps mimic nature's way.

Prebiotic synthesis of cysteine peptides that catalyze peptide ligation in neutral water. Science , 2020; 370 (6518): 865 DOI: 10.1126/science.abd5680 Cite This Page : ...

One of these, cysteine, was assumed not to have been present at the origin of life. ... "We have shown that nitriles possess the in-built energy required to form peptide bonds in water.