IRG and GBP Host Resistance Factors Target Aberrant, "Non-self" Vacuoles Characterized by the Missing of "Self" IRGM Proteins

PLoS Pathog. 2013 Jun;9(6):e1003414. doi: 10.1371/journal.ppat.1003414. Epub 2013 Jun 13.

IRG and GBP Host Resistance Factors Target Aberrant, "Non-self" Vacuoles Characterized by the Missing of "Self" IRGM Proteins

Haldar AK, Saka HA, Piro AS, Dunn JD, Henry SC, Taylor GA, Frickel EM, Valdivia RH, Coers J.

Departments of Molecular Genetics and Microbiology, and Immunology, Duke University Medical Center, Durham, North Carolina, United States of America.

Interferon-inducible GTPases of the Immunity Related GTPase (IRG) and Guanylate Binding Protein (GBP) families provide resistance to intracellular pathogenic microbes. IRGs and GBPs stably associate with pathogen-containing vacuoles (PVs) and elicit immune pathways directed at the targeted vacuoles. Targeting of Interferon-inducible GTPases to PVs requires the formation of higher-order protein oligomers, a process negatively regulated by a subclass of IRG proteins called IRGMs. We found that the paralogous IRGM proteins Irgm1 and Irgm3 fail to robustly associate with "non-self" PVs containing either the bacterial pathogen Chlamydia trachomatis or the protozoan pathogen Toxoplasma gondii. Instead, Irgm1 and Irgm3 reside on "self" organelles including lipid droplets (LDs). Whereas IRGM-positive LDs are guarded against the stable association with other IRGs and GBPs, we demonstrate that IRGM-stripped LDs become high affinity binding substrates for IRG and GBP proteins. These data reveal that intracellular immune recognition of organelle-like structures by IRG and GBP proteins is partly dictated by the missing of "self" IRGM proteins from these structures.

PMID: 23785284 [PubMed - in process]