Mycobacterium tuberculosis SatS is a chaperone for the SecA2 protein export pathway

Abstract
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Abstract

The SecA2 protein export system is critical for the virulence of Mycobacterium tuberculosis. However, the mechanism of this export pathway remains unclear. Through a screen for suppressors of a secA2 mutant, we identified a new player in the mycobacterial SecA2 pathway that we named SatS for SecA2 (two) Suppressor. In M. tuberculosis, SatS is required for the export of a subset of SecA2 substrates and for growth in macrophages. We further identify a role for SatS as a protein export chaperone. SatS exhibits multiple properties of a chaperone, including the ability to bind to and protect substrates from aggregation. Our structural studies of SatS reveal a distinct combination of a new fold and hydrophobic grooves resembling preprotein-binding sites of the SecB chaperone. These results are significant in better defining a molecular pathway for M. tuberculosis pathogenesis and in expanding our appreciation of the diversity among chaperones and protein export systems.

Data availability

All data generated and analysed during this study are included in the manuscript and supporting files. Figure supplements have been provided for Figures 1, 2, 5, and 8. Two additional supplementary tables describe the primers and plasmids used in this study. SatS C domain X-ray structure validation details are described in Figure 8-figure supplement 1 and have been deposited in PDB under the accession codes 6DRQ and 6DNM.

The following data sets were generated

(2019) The crystal structure of SatS c-terminal domain in complex with bromine
Protein Data Bank, 6DRQ.

https://www.rcsb.org/structure/6DRQ
(2019) The crystal structure of SatS c-terminal domain
Protein Data Bank, 6DNM.

https://www.rcsb.org/structure/6DNM

The following previously published data sets were used

(2003) Crystal Structure of SecB from Escherichia coli
Protein Data Bank, 1QYN.

https://www.rcsb.org/structure/1QYN

Article and author information

Author details

Brittany K Miller

Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, United States

Competing interests
The authors declare that no competing interests exist.
Ryan Hughes

Department of Biochemistry and Biophysics, Texas A&M University, College Station, United States

Competing interests
The authors declare that no competing interests exist.
Lauren S Ligon

Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, United States

Competing interests
The authors declare that no competing interests exist.
Nathan W Rigel

Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, United States

Competing interests
The authors declare that no competing interests exist.
Seidu Malik

Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, United States

Competing interests
The authors declare that no competing interests exist.
Brandon R Anjuwon-Foster

Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, United States

Competing interests
The authors declare that no competing interests exist.
James C Sacchettini

Department of Biochemistry and Biophysics, Texas A&M University, College Station, United States

Competing interests
The authors declare that no competing interests exist.
Miriam Braunstein

Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, United States

For correspondence
braunste@med.unc.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0003-1180-0030

Funding

National Institute of Allergy and Infectious Diseases (AI054540)

Brittany K Miller
Lauren S Ligon
Nathan W Rigel
Seidu Malik
Miriam Braunstein

National Institute of Allergy and Infectious Diseases (A-0015)

Ryan Hughes
James C Sacchettini

Welch Foundation (A-0015)

Ryan Hughes
James C Sacchettini

University of North Carolina (Graduate School Disseration Award)

Brittany K Miller

National Institute of General Medical Sciences (GM055336)

Brandon R Anjuwon-Foster

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: All animal care and experimental protocols were in strict accordance with the NIH Guide for the Care and Use of Laboratory Animals and were approved by the Institutional Animal Care and Use Committee of the University of North Carolina (protocol number 15-018.0).

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.