Abstract
We previously examined Salmonella proteome within infected host cells and found differential expression of many proteins with defined functional roles such as metabolism or virulence. However, the precise roles of other altered proteins in Salmonella pathogenesis are largely unknown. A putative transcriptional regulator, YdcR, was highly induced intracellularly whereas barely expressed in vitro, implicating potential relevance to bacterial infection. To unveil its physiological functions, we exploited quantitative proteomics of intracellular Salmonella and found that genetic ablation of ydcR resulted in severe repression of SrfN, a known virulence factor. Immunoblotting, qRT-PCR, and β-galactosidase assays further demonstrate YdcR-dependent transcription and expression of srfN Moreover, we found physical interaction of YdcR with the promoter region of srfN, suggesting direct activation of its transcription. Importantly, a Salmonella mutant lacking ydcR was markedly attenuated in a mouse model of infection. Our findings reveal that YdcR temporally regulates the virulence factor SrfN during infection, thus contributing to Salmonella pathogenesis. Our work also highlights the utility of combining quantitative proteomics and bacterial genetics for uncovering the functional roles of transcription factors and likely other uncharacterized proteins as well.
Highlights
From the ‡Institute of Analytical Chemistry and Synthetic and Functional Biomolecules Center, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China; §Department of Laboratory Medicine, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China; ¶Department of Microbiology & Immunology, Cornell University, Ithaca, New York 14853-6401
As an intracellular bacterial pathogen, S. typhimurium has the capability to invade nonphagocytic epithelial cells and proliferate with a membrane-bound compartment known as the Salmonellacontaining vacuoles (SCVs) [4]
YdcR is homologous to the family of a MocR/GabR-type transcriptional regulator that falls into the GntR superfamily, one of the most widespread families of bacterial transcription factors that regulate diverse biological processes [10, 11], but the function of YdcR in Salmonella pathogenesis remains elusive
Summary
From the ‡Institute of Analytical Chemistry and Synthetic and Functional Biomolecules Center, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China; §Department of Laboratory Medicine, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China; ¶Department of Microbiology & Immunology, Cornell University, Ithaca, New York 14853-6401. T3SS functions as a molecular syringe that is able to translocate bacterial virulence factors (effector proteins) directly into host cytosol. These T3SS effector proteins, upon delivery, can modulate various host cellular processes to promote bacterial infection as well as survival within host cells [3]. Our quantitative proteomic measurements suggest extensive bacterial adaptations to infected host epithelial cells. We identified a putative transcription factor YdcR that was highly induced throughout the infection process, though this protein was barely expressed (i.e. not detected in our proteomic measurements) in bacteria cultured in vitro. YdcR is homologous to the family of a MocR/GabR-type transcriptional regulator that falls into the GntR superfamily, one of the most widespread families of bacterial transcription factors that regulate diverse biological processes [10, 11], but the function of YdcR in Salmonella pathogenesis remains elusive
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