Structural Basis for Virulence Activation of Francisella tularensis

Brady A Travis; Kathryn M Ramsey; Samantha M Prezioso; Thomas Tallo; Jamie M Wandzilak; Allen Hsu; Mario Borgnia; Alberto Bartesaghi; Simon L Dove; Richard G Brennan; Maria A Schumacher

doi:10.1016/j.molcel.2020.10.035

Structural Basis for Virulence Activation of Francisella tularensis

Mol Cell. 2021 Jan 7;81(1):139-152.e10. doi: 10.1016/j.molcel.2020.10.035. Epub 2020 Nov 19.

Authors

Affiliations

¹ Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA.
² Division of Infectious Diseases, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA; Department of Cell and Molecular Biology and Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881, USA.
³ Division of Infectious Diseases, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
⁴ Department of Cell and Molecular Biology and Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881, USA.
⁵ Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709, USA.
⁶ Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA; Department of Computer Science, Duke University, Durham, NC 27708, USA.
⁷ Division of Infectious Diseases, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA. Electronic address: simon.dove@childrens.harvard.edu.
⁸ Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA. Electronic address: richard.brennan@duke.edu.
⁹ Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA. Electronic address: maria.schumacher@duke.edu.

Abstract

The bacterium Francisella tularensis (Ft) is one of the most infectious agents known. Ft virulence is controlled by a unique combination of transcription regulators: the MglA-SspA heterodimer, PigR, and the stress signal, ppGpp. MglA-SspA assembles with the σ⁷⁰-associated RNAP holoenzyme (RNAPσ⁷⁰), forming a virulence-specialized polymerase. These factors activate Francisella pathogenicity island (FPI) gene expression, which is required for virulence, but the mechanism is unknown. Here we report FtRNAPσ⁷⁰-promoter-DNA, FtRNAPσ⁷⁰-(MglA-SspA)-promoter DNA, and FtRNAPσ⁷⁰-(MglA-SspA)-ppGpp-PigR-promoter DNA cryo-EM structures. Structural and genetic analyses show MglA-SspA facilitates σ⁷⁰ binding to DNA to regulate virulence and virulence-enhancing genes. Our Escherichia coli RNAPσ^70-homodimeric EcSspA structure suggests this is a general SspA-transcription regulation mechanism. Strikingly, our FtRNAPσ⁷⁰-(MglA-SspA)-ppGpp-PigR-DNA structure reveals ppGpp binding to MglA-SspA tethers PigR to promoters. PigR in turn recruits FtRNAP αCTDs to DNA UP elements. Thus, these studies unveil a unique mechanism for Ft pathogenesis involving a virulence-specialized RNAP that employs two (MglA-SspA)-based strategies to activate virulence genes.

Keywords: Cryo-EM; Francisella tularensis; MglA-SspA; PigR; RNA polymerase; pathogenicity island; ppGpp; transcription; αCTD; σ70.

Publication types

Research Support, N.I.H., Extramural
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

DNA-Directed RNA Polymerases* / genetics
DNA-Directed RNA Polymerases* / metabolism
Escherichia coli / genetics
Escherichia coli / metabolism
Francisella tularensis* / genetics
Francisella tularensis* / metabolism
Francisella tularensis* / pathogenicity
Promoter Regions, Genetic*
Sigma Factor* / genetics
Sigma Factor* / metabolism
Virulence Factors* / genetics
Virulence Factors* / metabolism

Substances

Sigma Factor
Virulence Factors
RNA polymerase sigma 70
DNA-Directed RNA Polymerases

Abstract

Publication types

MeSH terms

Substances

Grants and funding