Ehrlichia chaffeensis Exploits Host SUMOylation Pathways To Mediate Effector-Host Interactions and Promote Intracellular Survival

Abstract

ABSTRACTEhrlichia chaffeensisis an obligately intracellular Gram-negative bacterium that selectively infects mononuclear phagocytes. We recently reported thatE. chaffeensisutilizes a type 1 secretion (T1S) system to export tandem repeat protein (TRP) effectors and demonstrated that these effectors interact with a functionally diverse array of host proteins. By way of these interactions, TRP effectors modulate host cell functions; however, the molecular basis of these interactions and their roles in ehrlichial pathobiology are not well defined. In this study, we describe the first bacterial protein posttranslational modification (PTM) by the small ubiquitin-like modifier (SUMO). TheE. chaffeensisT1S effector TRP120 is conjugated to SUMO at a carboxy-terminal canonical consensus SUMO conjugation motifin vitroand in human cells. In human cells, TRP120 was selectively conjugated with SUMO2/3 isoforms. Disruption of TRP120 SUMOylation perturbed interactions with known host proteins, through predicted SUMO interaction motif-dependent and -independent mechanisms.E. chaffeensisinfection did not result in dramatic changes in the global host SUMOylated protein profile, but a robust colocalization of predominately SUMO1 with ehrlichial inclusions was observed. Inhibiting the SUMO pathway with a small-molecule inhibitor had a significant impact onE. chaffeensisreplication and recruitment of the TRP120-interacting protein polycomb group ring finger protein 5 (PCGF5) to the inclusion, indicating that the SUMO pathway is critical for intracellular survival. This study reveals the novel exploitation of the SUMO pathway byEhrlichia, which facilitates effector-eukaryote interactions necessary to usurp the host and create a permissive intracellular niche.