# PPE Export by the Essential ESX-5 Secretion System in M. tuberculosis Virulence

> **NIH NIH R21** · UNIVERSITY OF MINNESOTA · 2021 · $232,500

## Abstract

PROJECT SUMMARY/ABSTRACT
Mycobacterium tuberculosis (Mtb) requires the ESX-5 Type VII protein secretion system for in vitro growth.
Because ESX-5 is essential, the role that ESX-5 plays in Mtb virulence and the proteins exported via ESX-5
that support Mtb replication remain poorly characterized. In the related pathogen Mycobacterium marinum,
ESX-5 exports many proteins of the PE and PPE protein families that are unique to the mycobacteria. Several
Mtb PE and PPE proteins localize to the cell wall and were recently implicated in acquisition of diverse
nutrients. The prevailing model of PE and PPE secretion suggests they are exported as heterodimers that pair
uniquely and that export is promoted by an EspG chaperone that targets the PE-PPE pair to the cognate ESX
secretion system for export. This proposal will test the central hypothesis that Mtb requires ESX-5 activity and
a subset of ESX-5 substrates that are exported independently of the EspG5 chaperone for virulence. This
hypothesis is based on preliminary data using Mtb strains in which EccD5, an ESX-5 secretion machinery
subunit, or the EspG5 chaperone can be conditionally depleted. Depletion of EccD5 but not EspG5 limited Mtb
growth in macrophages and on certain carbon sources. Specific Aim 1 will determine the role of ESX-5 and the
EspG5 chaperone in Mtb virulence using conditional depletion of EccD5 or EspG5 and both macrophage and
mouse aerosol infection models. Specific Aim 2 will use the ESX-5 conditional depletion strains to identify PPE
proteins that require ESX-5 activity but not the EspG5 chaperone for export and connect ESX-5 activity to use
of specific nutrients. Specific Aim 3 will examine functional redundancy between PE proteins in facilitating
export of certain PPE proteins and promoting Mtb virulence using the mouse aerosol infection model. The
proposed research is conceptually innovative because it challenges existing models of ESX-5 substrate export
by suggesting promiscuous pairing between PE and PPE proteins and export of certain PPE proteins
independent of the EspG5 chaperone. The proposed research is significant because it is expected to show that
Mtb requires ESX-5 activity for pathogenesis. This knowledge would establish ESX-5 as a strategic target for
development of new anti-tubercular drugs and support inclusion of ESX-5-secreted antigens in new
tuberculosis vaccines.

## Key facts

- **NIH application ID:** 10286476
- **Project number:** 1R21AI163580-01
- **Recipient organization:** UNIVERSITY OF MINNESOTA
- **Principal Investigator:** Anna DeGraff Tischler
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $232,500
- **Award type:** 1
- **Project period:** 2021-07-01 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10286476

## Citation

> US National Institutes of Health, RePORTER application 10286476, PPE Export by the Essential ESX-5 Secretion System in M. tuberculosis Virulence (1R21AI163580-01). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10286476. Licensed CC0.

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