Figure 8.

Proposed model for hPI31 interaction with 20S proteasome.A, the low-pass filtered EM map of 20S proteasome surface rendered at a low threshold of σ = 2. B, the low-pass filtered EM map of PI31-bound 20S proteasome surface rendered at a low threshold with σ = 2. C, difference map (pink surface) between the two above-mentioned low-pass filtered EM maps revealing extra PI31 densities inside both catalytic and antechambers. The 20S atomic model is superimposed to indicate the chamber location of the difference densities. D, alternative models of the PI31–20S proteasome complex involving either monomeric (left) or dimeric (right) PI31 showing the interaction of the PI31 C-terminal domain with proteasome catalytic sites (see text for details).