Tripeptidyl peptidase II is a component of the proteolytic cascade acting downstream of the 26S proteasome in the ubiquitin-proteasome pathway. It may be able to complement the 26S proteasome function to some extent under conditions in which the latter is inhibited.
Tripeptidyl peptidase II is a mammalian peptidase that, at neutral pH, removes tripeptides from the N terminus of longer peptides. The protein has a specialized function that is essential for some MHC class I antigen presentation. The protein is a high molecular mass serine exopeptidase; the amino acid sequence surrounding the serine residue at the active site is similar to the peptidases of the subtilisin class rather than the trypsin class.