Suppressor analysis to identify proteins that work with the Mycobacterium smegmatis SecA2 protein export system Public Deposited

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  • March 21, 2019
  • Ligon, Lauren Stone
    • Affiliation: School of Medicine, Department of Microbiology and Immunology
  • Mycobacterium tuberculosis, the causative agent of the disease tuberculosis, is a serious threat to human health, responsible for 1.4 million deaths annually. When M. tuberculosis is spread from person to person by aerosol and is phagocytosed by alveolar macrophages, the proteins exported by the bacterium are ideally positioned to interact with the host. Therefore, exported proteins and the systems responsible for their export are important for M. tuberculosis virulence. All bacteria, including mycobacteria, contain the Sec protein export system, which is responsible for the bulk of protein export and is composed of a motor ATPase protein, SecA, and a membrane-embedded channel complex, SecYEG. Mycobacteria, including both M. tuberculosis and the model organism Mycobacterium smegmatis, along with some Gram-positive bacteria, are unique in containing two functionally distinct SecA proteins. The SecA protein responsible for housekeeping protein export is termed SecA1 and is essential for cell survival, while the second SecA protein, termed SecA2, is required for the export of a small subset of proteins and is important for M. tuberculosis virulence. While the canonical Sec system is well understood, the mechanism of SecA2-dependent export is not. Like canonical SecA proteins, the mycobacterial SecA2 requires ATPase activity to function. Furthermore, an M. smegmatis secA2 mutant (secA2 K129R) that encodes a SecA2 protein defective in ATP binding is dominant negative and appears to be trapped in a complex with interacting proteins at the membrane. Here, we analyze extragenic suppressors of secA2 K129R in an effort to better understand SecA2-dependent export and identify additional components of the SecA2 pathway. Using this approach, we demonstrate a connection between M. smegmatis SecA2 and SecY, the major membrane-embedded component of the housekeeping Sec export channel. In addition, we demonstrate a connection between the SecA2 system and Msmeg_1684, a protein of unknown function that is found throughout mycobacteria and may represent a novel component of the SecA2 pathway. Our findings suggest a new model in which the mycobacterial SecA2 export pathway is integrated into the housekeeping Sec pathway and includes an additional SecA2-specific component, Msmeg_1684.
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  • In Copyright
  • Braunstein, Miriam
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill
Graduation year
  • 2013

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