Cargo competition for a dimerization interface restricts and stabilizes a bacterial protease adaptor

Significance Energy-dependent proteases broadly regulate bacterial physiology and development. Adaptor proteins tune the substrate specificity of proteases by selectively delivering cargo and themselves can be degraded. We find that the RcdA adaptor forms homodimers that are degraded by the ClpXP protease. Cargo binding disrupts the dimer interface, stabilizing the adaptor, and provides a model for how adaptor degradation can be controlled. Mapping the surfaces responsible for cargo binding shows that different overlapping regions of the dimer interface are tailored to different substrates. Our results suggest a mode of control that provides robust adaptor activity subject to buffering by cargo demand.