Figure 8.

Adaptor proteins mediate degradation of some substrates. (A) The adaptor protein SspB (green) binds to ClpX (brown) through long flexible tails and to a substrate (blue) through the ssrA degradation tag (red), allowing it to present the substrate to ClpX. (B) The adaptor protein Rad23 contains a UbL domain (purple) that binds to receptors on the proteasome such as Rpn13, as well as two UBA domains (green) that can bind to ubiquitinated substrates (blue) and present them to the proteasome for degradation. The flexible linkers connecting Rad23 domains may help position substrates of different geometry such that their unstructured initiation regions (red) can engage with the proteasomal motors.