title: Peptidoglycan recognition proteins kill bacteria by inducing oxidative, thiol, and metal stress.
abstract: Mammalian Peptidoglycan Recognition Proteins (PGRPs) are a family of evolutionary conserved bactericidal innate immunity proteins, but the mechanism through which they kill bacteria is unclear. We previously proposed that PGRPs are bactericidal due to induction of reactive oxygen species (ROS), a mechanism of killing that was also postulated, and later refuted, for several bactericidal antibiotics. Here, using whole genome expression arrays, qRT-PCR, and biochemical tests we show that in both Escherichia coli and Bacillus subtilis PGRPs induce a transcriptomic signature characteristic of oxidative stress, as well as correlated biochemical changes. However, induction of ROS was required, but not sufficient for PGRP killing. PGRPs also induced depletion of intracellular thiols and increased cytosolic concentrations of zinc and copper, as evidenced by transcriptome changes and supported by direct measurements. Depletion of thiols and elevated concentrations of metals were also required, but by themselves not sufficient, for bacterial killing. Chemical treatment studies demonstrated that efficient bacterial killing can be recapitulated only by the simultaneous addition of agents leading to production of ROS, depletion of thiols, and elevation of intracellular metal concentrations. These results identify a novel mechanism of bacterial killing by innate immunity proteins, which depends on synergistic effect of oxidative, thiol, and metal stress and differs from bacterial killing by antibiotics. These results offer potential targets for developing new antibacterial agents that would kill antibiotic-resistant bacteria.
authors.affiliation: Indiana University School of Medicine-Northwest, Gary, Indiana, United States of America.
authors.forename: Des Raj
authors.initials: DR
authors.lastname: Kashyap
authors.affiliation: Indiana University School of Medicine-Northwest, Gary, Indiana, United States of America.
authors.forename: Annemarie
authors.initials: A
authors.lastname: Rompca
authors.affiliation: Department of Microbiology, Cornell University, Ithaca, New York, United States of America.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Gaballa
authors.affiliation: Department of Microbiology, Cornell University, Ithaca, New York, United States of America.
authors.forename: John D
authors.initials: JD
authors.lastname: Helmann
authors.affiliation: Departments of Chemistry and Molecular and Cell Biology and the Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, California, United States of America.
authors.forename: Jefferson
authors.initials: J
authors.lastname: Chan
authors.affiliation: Departments of Chemistry and Molecular and Cell Biology and the Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, California, United States of America.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Chang
authors.affiliation: Department of Mathematics, Indiana University Northwest, Gary, Indiana, United States of America.
authors.forename: Iztok
authors.initials: I
authors.lastname: Hozo
authors.affiliation: Indiana University School of Medicine-Northwest, Gary, Indiana, United States of America.
authors.forename: Dipika
authors.initials: D
authors.lastname: Gupta
authors.affiliation: Indiana University School of Medicine-Northwest, Gary, Indiana, United States of America.
authors.forename: Roman
authors.initials: R
authors.lastname: Dziarski
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008670:Metals / Q000378:metabolism*; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D008670:Metals; D017382:Reactive Oxygen Species; D013438:Sulfhydryl Compounds; C118897:peptidoglycan recognition protein