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Humanity's ongoing struggle with new, re-emerging and endemic infectious diseases serves as a frequent reminder of the need to understand host-pathogen interactions. Recent advances in genomics have dramatically advanced our understanding of how genetics contributes to host resistance or susceptibility to bacterial infection. Here we discuss current trends in defining host-bacterial interactions at the genome-wide level, including screens that harness CRISPR/Cas9 genome editing, natural genetic variation, proteomics, and transcriptomics. We report on the merits, limitations, and findings of these innovative screens and discuss their complementary nature. Finally, we speculate on future innovation as we continue to progress through the postgenomic era and towards deeper mechanistic insight and clinical applications.

Bacteria masterfully co-opt and subvert host signal transduction. As a paradigmatic example, Salmonella uses two type-3 secretion systems to inject effector proteins that facilitate Salmonella entry, establishment of an intracellular niche, and modulation of immune responses. We previously demonstrated that the Salmonella anti-inflammatory response activator SarA (Stm2585, GogC, PagJ, SteE) activates the host transcription factor STAT3 to drive expression of immunomodulatory STAT3-targets. Here, we demonstrate-by sequence, function, and biochemical measurement-that SarA mimics the cytoplasmic domain of glycoprotein 130 (gp130, IL6ST). SarA is phosphorylated at a YxxQ motif, facilitating binding to STAT3 with greater affinity than gp130. Departing from canonical gp130 signaling, SarA function is JAK-independent but requires GSK-3, a key regulator of metabolism and development. Our results reveal that SarA undergoes host phosphorylation to recruit a STAT3-activating complex, circumventing cytokine receptor activation. Effector mimicry of gp130 suggests GSK-3 can regulate normal cytokine signaling, potentially enabling metabolic and immune crosstalk.

The cholesterol storage disorder Niemann-Pick type C (NPC) disease is caused by defects in either of two late endosomal/lysosomal proteins, NPC1 and NPC2. NPC2 is a 16-kDa soluble protein that binds cholesterol in a 1:1 stoichiometry and can transfer cholesterol between membranes by a mechanism that involves protein-membrane interactions. To examine the structural basis of NPC2 function in cholesterol trafficking, a series of point mutations were generated across the surface of the protein. Several NPC2 mutants exhibited deficient sterol transport properties in a set of fluorescence-based assays. Notably, these mutants were also unable to promote egress of accumulated intracellular cholesterol from npc2(-/-) fibroblasts. The mutations mapped to several regions on the protein surface, suggesting that NPC2 can bind to more than one membrane simultaneously. Indeed, we have previously demonstrated that WT NPC2 promotes vesicle-vesicle interactions. These interactions were abrogated, however, by mutations causing defective sterol transfer properties. Molecular modeling shows that NPC2 is highly plastic, with several intense positively charged regions across the surface that could interact favorably with negatively charged membrane phospholipids. The point mutations generated in this study caused changes in NPC2 surface charge distribution with minimal conformational changes. The plasticity, coupled with membrane flexibility, probably allows for multiple cholesterol transfer routes. Thus, we hypothesize that, in part, NPC2 rapidly traffics cholesterol between closely appositioned membranes within the multilamellar interior of late endosomal/lysosomal proteins, ultimately effecting cholesterol egress from this compartment.