Mechanisms of action of Coxiella burnetii effectors inferred from host-pathogen protein interactions

Abstract

Coxiella burnetii is an obligate Gram-negative intracellular pathogen and the etiological agent of Q fever. Successful infection requires a functional Type IV secretion system, which translocates more than 100 effector proteins into the host cytosol to establish the infection, restructure the intracellular host environment, and create a parasitophorous vacuole where the replicating bacteria reside. We used yeast two-hybrid (Y2H) screening of 33 selected C. burnetii effectors against whole genome human and murine proteome libraries to generate a map of potential host-pathogen protein-protein interactions (PPIs). We detected 273 unique interactions between 20 pathogen and 247 human proteins, and 157 between 17 pathogen and 137 murine proteins. We used orthology to combine the data and create a single host-pathogen interaction network containing 415 unique interactions between 25 C. burnetii and 363 human proteins. We further performed complementary pairwise Y2H testing of 43 out of 91 C. burnetii-human interactions involving five pathogen proteins. We used the combined data to 1) perform enrichment analyses of target host cellular processes and pathways, 2) examine effectors with known infection phenotypes, and 3) infer potential mechanisms of action for four effectors with uncharacterized functions. The host-pathogen interaction profiles supported known Coxiella phenotypes, such as adapting cell morphology through cytoskeletal re-arrangements, protein processing and trafficking, organelle generation, cholesterol processing, innate immune modulation, and interactions with the ubiquitin and proteasome pathways. The generated dataset of PPIs—the largest collection of unbiased Coxiella host-pathogen interactions to date—represents a rich source of information with respect to secreted pathogen effector proteins and their interactions with human host proteins.

The Coxiella burnetii effector protein CaeB modulates endoplasmatic reticulum ( ER) stress signalling and is required for efficient replication in Galleria mellonella

“…Indeed chemical inhibition of the UPR antagonises the expansion of the CCV (Brann et al, 2020). Several C. burnetii effector proteins have been identified by a yeast‐based interaction screen to target ER host proteins (Wallqvist et al, 2017). One ER localised C. burnetii T4BSS effector protein is ElpA (Graham, Winchell, Sharma, & Voth, 2015; Weber et al, 2013), which triggers disruption of ER structure (Graham et al, 2015).…”

Subversion of the Endocytic and Secretory Pathways by Bacterial Effector Proteins

“…While great strides have been made toward understanding how effector proteins manipulate host processes to redirect membrane and nutrients to the parasitophorous vacuoles, the function of most effector proteins still remains ill-defined and genetic manipulation of some of these organism presents specific challenges. Large-scale screens to identify putative binding partners of ectopically produced type III secreted effectors (Mirrashidi et al, 2015 ) or yeast-2-hybrid screening of type IV secreted effectors (Wallqvist et al, 2017 ) has identified potential interacting partners for many previously uncharacterized effector proteins. While these seminal studies will serve as a useful starting point for elucidating effector function of uncharacterized secretion substrates, many of these interactions still require validation.…”

Targeting host lipid flows: Exploring new antiviral and antibiotic strategies

“…ORP1L acts as a cholesterol sensor that modulates the formation of MCSs between the late endosomes and the ER. It has been recently reported that Coxiella recruits ORP1L to MCSs formed between the bacterial inclusion and the ER, which is followed by changes in the membrane properties of the inclusion vacuole (Justis et al, ; Wallqvist et al, ). ORP1L attaches to the Coxiella ‐containing vacuole membrane through its N‐terminal ankyrin repeats that are involved in protein–protein interactions, but the specific function of ORP1L in the infection is still unclear.…”