The Ub-CHOP2-Reporter Deubiquitination Assay consists of ubiquitin fused to a reporter enzyme, as well as a separate reagent substrate for the reporter enzyme. When fused to ubiquitin, the reporter is rendered catalytically inactive. Following cleavage of the Ub-reporter system by the isopeptidase, the free (and now active) reporter subsequently acts upon its substrate. Thus, in this coupled assay, the signal generated by cleavage of the reporter enzyme’s substrate is a quantitative measure of isopeptidase activity.
This assay utilizes the two classes of ubiquitin: ubiquitin-like proteins (UBL) and ubiquitin-domain proteins (UDP). The UBLs function as modifiers in a manner analogous to that of ubiquitin. Examples consist of (and are available for this assay) SUMO, Nedd8 (aka Rub1), ISH15, Apg8, APg12, and Fat10. The UDPs consist of parkin, RAD23, and DSK2, and are designated ubiquitin-domain proteins that contain domains that are related to ubiquitin.