Flexible Client-Dependent Cages in the Assembly Landscape of the Periplasmic Protease-Chaperone DegP

Theperiplasmic protein DegP, which is implicated in virulencefactor transport leading to pathogenicity, is a bi-functional proteaseand chaperone that helps to maintain protein homeostasis in Gram-negativebacteria and is essential to bacterial survival under stress conditions.To perform these functions, DegP captures clients inside cage-likestructures, which we have recently shown to form through the reorganizationof high-order preformed apo oligomers, consisting of trimeric buildingblocks, that are structurally distinct from client-bound cages. Ourprevious studies suggested that these apo oligomers may allow DegPto encapsulate clients of various sizes under protein folding stressesby forming ensembles that can include extremely large cage particles,but how this occurs remains an open question. To explore the relationbetween cage and substrate sizes, we engineered a series of DegP clientsof increasing hydrodynamic radii and analyzed their influence on DegPcage formation. We used dynamic light scattering and cryogenic electronmicroscopy to characterize the hydrodynamic properties and structuresof the DegP cages that are adopted in response to each client. Wepresent a series of density maps and structural models that includethose for novel particles of approximately 30 and 60 monomers. Keyinteractions between DegP trimers and the bound clients that stabilizethe cage assemblies and prime the clients for catalysis are revealed.We also provide evidence that DegP can form cages which approach subcellularorganelles in terms of size.

Automated summary

DegP is a periplasmic protein involved in the transport of pathogenicity-related virulence factors. It functions as a bi-functional protease and chaperone to maintain protein homeostasis in Gram-negative bacteria under stress conditions. It forms cage-like structures by reorganizing high-order preformed apo oligomers, which can encapsulate clients of various sizes.