Threonine proteases are proteases that have threonine, an amino acid, bonded at the active site. It is responsible for functioning proteasome, the large protein-degrading apparatus. Threonine proteases haveaA conserved N-terminal threonine at each active site. Pre-proteins, which are catalytic beta subunits, are activated when the N-terminus is cleaved off. This makes threonine the N-terminal residue.
Threonine proteases are activated by primary amines. The mechanism for the threonine protease was described first in 1995. The mechanism showed the cleaving of a peptide bond which made an amino acid residue (usually serine, threonine, or cysteine) or a water molecule become a good nucleophile which could perform a nucleophilic attack on the carboxyl group of the peptide. The amino acid residue (in this case threonine) is usually activated by a histidine residue.