The endoplasmic reticulum aminopeptidases (ERAP)1 and ERAP2 play a critical role 
in the production of final epitopes presented by MHC class I molecules. 
Formation of heterodimers by ERAP1 and ERAP2 has been proposed to facilitate 
trimming of epitope precursor peptides, but the effects of dimerization on ERAP 
function remain unknown. In this study, we produced stabilized ERAP1-ERAP2 
heterodimers and found that they produced several mature epitopes more 
efficiently than a mix of the two enzymes unable to dimerize. Physical 
interaction with ERAP2 changes basic enzymatic parameters of ERAP1 and improves 
its substrate-binding affinity. Thus, by bringing the two enzymes in proximity 
and by producing allosteric effects on ERAP1, dimerization of ERAP1/2 creates 
complexes with superior peptide-trimming efficacy. Such complexes are likely to 
enhance Ag presentation by cells displaying coordinated expression of the two 
enzymes.