A
catalytic triad refers to the three
amino acid residues that function together at the centre of the
active site of some
hydrolase and
transferase enzymes (e.g.
proteases,
amidases,
esterases, acylases,
lipases and
ß-lactamases). An
Acid-
Base-
Nucleophile triad is a common motif for generating a nucleophilic residue for
covalent catalysis. The
residues form a charge-relay network to polarise and activate the nucleophile, which attacks the
substrate, forming a
covalent intermediate which is then
hydrolysed to regenerate free enzyme. The nucleophile is most commonly a
serine or
cysteine amino acid, but occasionally
threonine. Because enzymes fold into complex
three-dimensional structures, the residues of a catalytic triad can be far from each other along the amino-acid sequence (
primary structure), however, they are brought close together in the final fold.