Approaches to Evaluate the Impact of a Small-Molecule Binder to a Noncatalytic Site of the Proteasome.

Proteasome activity is crucial for cell survival and proliferation. In recent years, small molecules have been discovered that can affect the catalytic activity of the proteasome. Rather than targeting the active sites of the proteasome, it might be possible to affect ubiquitin-dependent degradation of proteins by limiting the association of the 19S regulatory particle (19S RP) with the 20S core particle (20S CP) of the proteasome. We recently described the discovery of TXS-8, a peptoid that binds to Rpn-6. Rpn-6 is a proteasome-associated protein that makes critical contacts with the 19S RP and the 20S CP. Herein, we present a general workflow to evaluate the impact of a small-molecule binder on proteasome activity by using TXS-8 as an example. This workflow contains three steps in which specific probes or overexpressed proteins in cells are used to determine whether the hydrolysis activity of the proteasome is affected. Although, in our case, TXS-8 did not affect proteasome activity, our workflow is highly amenable to studying a variety of small-molecule-proteasome subunit interactions.