National Center for
5L5Q: Yeast 20s Proteasome With Human Beta5i (1-138) And Human Beta6 (97- 111; 118-133) In Complex With Epoxyketone 18
A humanized yeast proteasome identifies unique binding modes of inhibitors for the immunosubunit beta5i
EMBO J. (2016) 35 p.2602-2613
Inhibition of the immunoproteasome subunit beta5i alleviates autoimmune diseases in preclinical studies and represents a promising new anti-inflammatory therapy. However, the lack of structural data on the human immunoproteasome still hampers drug design. Here, we systematically determined the potency of seven alpha' beta' epoxyketone inhibitors with varying N-caps and P3-stereochemistry for mouse/human beta5c/beta5i and found pronounced differences in their subunit and species selectivity. Using X-ray crystallography, the compounds were analyzed for their modes of binding to chimeric yeast proteasomes that incorporate key parts of human beta5c, human beta5i or mouse beta5i and the neighboring beta6 subunit. The structural data reveal exceptional conformations for the most selective human beta5i inhibitors and highlight subtle structural differences as the major reason for the observed species selectivity. Altogether, the presented results validate the humanized yeast proteasome as a powerful tool for structure-based development of beta5i inhibitors with potential clinical applications.