Bacterial pathogens are a threat to global health and have evolved elaborate strategies to infect their hosts. One potent bacterial weapon in the war between host and pathogen is the Type IV secretion system (T4SS), found in a wide variety of bacterial species, including those that cause human disease, such as Legionella pneumophila, Helicobacter pylori, Bordetella pertussis, Brucella, Bartonella, and Coxiella. The L. pneumophila, T4SS translocates 100s of effector proteins into the host cell and is essential for pathogenesis. T4SSs are challenging complexes to work with because they span the inner and outer membranes of Gram-negative bacteria and contain a minimum of 12 proteins. Studies in prototype systems, such as E. coli plasmids and A. tumefaciens show that T4SSs are generally organized into an outer membrane core complex (OMCC), an inner membrane complex (IMC), and in some species an extracellular pilus. While there are no published high- resolution (sub-3.5 ) structures of an entire T4SS; there are sub-3.5 structures of OMCCs from both the Xanthomonas citri and conjugation system that translocate DNA. In contrast to the DNA-translocating T4SSs, the L. pneumophila T4SS is composed of ~26 components and low resolution (~30 ) cryo-electron tomography studies show that this T4SS has an enlarged OMCC and contains periplasmic densities not seen in the structures of minimized E. coli and X. citri T4SSs. The lack of detailed structural information limits our mechanistic understanding of how the L. pneumophila T4SS functions and contributes to pathogenesis. The focus of this proposal is to use a combination of structural and genetic approaches to construct the first detailed molecular map of the organization of the L. pneumophila T4SS. These high resolution models will be used to address fundamental questions such as whether there are conserved structural components shared among T4SSs that can be exploited for new anti-bacterial treatment strategies, how T4SSs are tuned to export proteins versus nucleic acids, and how export of effectors is regulated.

Public Health Relevance

Bacteria use numerous approaches in the war against host cells including the deployment of Type IV secretion systems (T4SSs) to aid in colonizing hosts, transferring antibiotic resistance genes between bacteria, and forming biofilms. There is no high-resolution structure (sub 3.5 ) of any protein-translocating T4SS, leaving a significant gap in our understanding of how T4SS transport molecules and are regulated. The focus of this proposal is to use a combination of cryo-electron microscopy and genetic approaches to develop a mechanistic model for how the protein-translocating Legionella pneumophila T4SS delivers effector proteins into host cells during pathogenesis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Postdoctoral Individual National Research Service Award (F32)
Project #
5F32AI150027-02
Application #
10084702
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Ernst, Nancy L
Project Start
2020-01-01
Project End
2022-12-31
Budget Start
2021-01-01
Budget End
2021-12-31
Support Year
2
Fiscal Year
2021
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Type
Organized Research Units
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109