Threonine

Threonine proteases are not yet classified into clans but are divided into six families: T1, T2, T3, T5, T7, and T8. Peptidase family T1 contains the component peptidases of the proteasome and related compound peptidases. During the catalysis, the N-terminal threonine residues of some of the beta subunits acts as the nucleophiles (Seemuller et al., 1995). Due to its resistence to inhibition by most standard peptidase inhibitors, the catalytic type of the proteasome were difficult to understand. The fourteen subunits are revealed in the complex structure and the catalytic residues of some of the subunits be the N-terminal threonine. Inhibition by natural inhibitors is not known.