Identification of ElpA, a Coxiella burnetii pathotype-specific Dot/Icm type IV secretion system substrate

• Published in: Infection and immunity Vol. 83; no. 3; pp. 1190 - 1198
• Main Authors: Graham, Joseph G, Winchell, Caylin G, Sharma, Uma M, Voth, Daniel E
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01-03-2015
• Subjects: Amino Acid Sequence; Animals; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacterial Secretion Systems - genetics; Carrier Proteins - chemistry; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Line; Cellular Microbiology: Pathogen-Host Cell Molecular Interactions; Coxiella burnetii; Coxiella burnetii - chemistry; Coxiella burnetii - genetics; Coxiella burnetii - metabolism; Coxiella burnetii - pathogenicity; Endoplasmic Reticulum - chemistry; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum - ultrastructure; Gene Expression; HEK293 Cells; HeLa Cells; Humans; Molecular Sequence Data; Monocytes - cytology; Monocytes - metabolism; Mutation; Open Reading Frames; Plasmids; Protein Sorting Signals; Protein Structure, Secondary; Protein Structure, Tertiary; Protein Transport - genetics; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Transgenes
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.02855-14

Coxiella burnetii causes human Q fever, a zoonotic disease that presents with acute flu-like symptoms and can result in chronic life-threatening endocarditis. In human alveolar macrophages, C. burnetii uses a Dot/Icm type IV secretion system (T4SS) to generate a phagolysosome-like parasitophorous vacuole (PV) in which to replicate. The T4SS translocates effector proteins, or substrates, into the host cytosol, where they mediate critical cellular events, including interaction with autophagosomes, PV formation, and prevention of apoptosis. Over 100 C. burnetii Dot/Icm substrates have been identified, but the function of most remains undefined. Here, we identified a novel Dot/Icm substrate-encoding open reading frame (CbuD1884) present in all C. burnetii isolates except the Nine Mile reference isolate, where the gene is disrupted by a frameshift mutation, resulting in a pseudogene. The CbuD1884 protein contains two transmembrane helices (TMHs) and a coiled-coil domain predicted to mediate protein-protein interactions. The C-terminal region of the protein contains a predicted Dot/Icm translocation signal and was secreted by the T4SS, while the N-terminal portion of the protein was not secreted. When ectopically expressed in eukaryotic cells, the TMH-containing N-terminal region of the CbuD1884 protein trafficked to the endoplasmic reticulum (ER), with the C terminus dispersed nonspecifically in the host cytoplasm. This new Dot/Icm substrate is now termed ElpA (ER-localizing protein A). Full-length ElpA triggered substantial disruption of ER structure and host cell secretory transport. These results suggest that ElpA is a pathotype-specific T4SS effector that influences ER function during C. burnetii infection.