BIOPHYSICS SEMINAR<br>Mechanisms of Regulated Protein Degradation During the Bacterial Cell Cycle</br>
Energy dependent protein degradation ensures the complete and immediate destruction of undesired proteins with stringent selectivity. In the bacteria Caulobacter crescentus the essential AAA+ protease ClpXP coordinates replication with differentiation via regulated proteolysis of key cell cycle factors. Using a substrate trapping approach, we have identified several new pathways that are regulated through proteolysis and revealed new features of protein degradation, such as the role of partial processing in generating essential functional diversity. Although proteases can directly recognize many targets, auxiliary factors known as adaptors can dramatically alter the substrate landscape for a given protease. In Caulobacter, additional factors such as RcdA and CpdR are crucial for regulated proteolysis by ClpXP during the cell cycle, but how they influence their substrates remains poorly understood. Here, we describe how these additional factors alter protease selectivity by hierarchically assembling into adaptor hubs. These hubs allow for dynamic, yet selective, substrate recognition and enable the cell to rapidly diversify proteolysis.