Concerted peptide trimming by human ERAP1 and ERAP2 aminopeptidase complexes in the endoplasmic reticulum

Abstract

The generation of many HLA class I peptides entails a final trimming step in the endoplasmic reticulum that, in humans, is accomplished by two 'candidate' aminopeptidases. We show here that one of these, ERAP1, was unable to remove several N-terminal amino acids that were trimmed efficiently by the second enzyme, ERAP2. This trimming of a longer peptide required the concerted action of both ERAP1 and ERAP2, both for in vitro digestion and in vivo for cellular antigen presentation. ERAP1 and ERAP2 localized together in vivo and associated physically in complexes that were most likely heterodimeric. Thus, the human endoplasmic reticulum is equipped with a pair of trimming aminopeptidases that have complementary functions in HLA class I peptide presentation.

ERAP1–ERAP2 Dimerization Increases Peptide-Trimming Efficiency

“…When probing with single-amino-bond fluorogenic substrates, ERAP1 prefers hydrophobic amino acids (leucine, methionine), whereas ERAP2 displays selectivity for positively charged amino acids (arginine, lysine) (5,(9)(10)(11). However, the activity of both enzymes toward more physiological, longer substrates appears to be less restrictive (5, 9-11) and depends on additional factors such as the C terminus (12) and the internal sequence of peptides (13,14).…”

Identification of potential HLA class I and class II epitope precursors associated with heat shock protein 70 (HSPA)

“…However, the generation of correct Ctermini has also been attributed to tripeptidyl peptidase II (TPPII) which has been shown to be essential for producing particular epitopes (Geier et al 1999;Seifert et al 2003). Peptides from the cytosol are transported by the transporter associated with antigen processing (TAP) to the endoplasmic reticulum (ER) (Kleijmeer et al 1992) where their Ntermini are specifically trimmed, in the final step of antigen generation, to a particular size of eight or nine residues by ER-associated aminopeptidases (Saveanu et al 2005;York et al 2002). HLA class II, in contrast, is specifically expressed by APCs which take up exogenous antigen precursors and transport them to the MHC class II compartment (MIIC) where antigen generation takes place (Neefjes et al 1990).…”

MHC Class I Quality Control

“…After the peptides have been transported by TAP into the ER they may be further trimmed by aminopeptidases such as ER aminopeptidases 1 and 2 (ERAP1 and ERAP2) (Saric, Chang et al 2002;Serwold, Gonzalez et al 2002;Saveanu, Carroll et al 2005). Although both are members of the M1 family of zinc metolloproteases (Rawlings, Barrett et al 2010) ERAP1 and ERAP2 show striking differences in their substrate preferences.…”

“…Although both are members of the M1 family of zinc metolloproteases (Rawlings, Barrett et al 2010) ERAP1 and ERAP2 show striking differences in their substrate preferences. ERAP1 has a preference for large hydrophobic residues while ERAP2 prefers basic residues (Hattori, Kitatani et al 2000;Tanioka, Hattori et al 2003;Saveanu, Carroll et al 2005). In contrast to most other aminopeptidases, that are more or less restricted to cleaving peptides shorter than four residues, ERAP1 shows a strong increase in cleaving activity towards peptides that are between 10-16 residues long (York, Chang et al 2002).…”

“…In contrast to most other aminopeptidases, that are more or less restricted to cleaving peptides shorter than four residues, ERAP1 shows a strong increase in cleaving activity towards peptides that are between 10-16 residues long (York, Chang et al 2002). As ERAP1 and ERAP2 cleave substrates with different preferential for the N-terminal residues ERAP1 and ERAP2 have been suggested to work in concert for trimming of MHC-I binding peptides (Saveanu, Carroll et al 2005).…”