title: Label-free Quantitative Proteomics Reveals a Role for the Mycobacterium tuberculosis SecA2 Pathway in Exporting Solute Binding Proteins and Mce Transporters to the Cell Wall.
abstract: Mycobacterium tuberculosis is an example of a bacterial pathogen with a specialized SecA2-dependent protein export system that contributes to its virulence. Our understanding of the mechanistic basis of SecA2-dependent export and the role(s) of the SecA2 pathway in M. tuberculosis pathogenesis has been hindered by our limited knowledge of the proteins exported by the pathway. Here, we set out to identify M. tuberculosis proteins that use the SecA2 pathway for their export from the bacterial cytoplasm to the cell wall. Using label-free quantitative proteomics involving spectral counting, we compared the cell wall and cytoplasmic proteomes of wild type M. tuberculosis to that of a ΔsecA2 mutant. This work revealed a role for the M. tuberculosis SecA2 pathway in the cell wall localization of solute binding proteins that work with ABC transporters to import solutes. Another discovery was a profound effect of SecA2 on the cell wall localization of the Mce1 and Mce4 lipid transporters, which contribute to M. tuberculosis virulence. In addition to the effects on solute binding proteins and Mce transporter export, our label-free quantitative analysis revealed an unexpected relationship between SecA2 and the hypoxia-induced DosR regulon, which is associated with M. tuberculosis latency. Nearly half of the transcriptionally controlled DosR regulon of cytoplasmic proteins were detected at higher levels in the ΔsecA2 mutant versus wild type M. tuberculosis. By increasing the list of M. tuberculosis proteins known to be affected by the SecA2 pathway, this study expands our appreciation of the types of proteins exported by this pathway and guides our understanding of the mechanism of SecA2-dependent protein export in mycobacteria. At the same time, the newly identified SecA2-dependent proteins are helpful for understanding the significance of this pathway to M. tuberculosis virulence and physiology.
authors: From the ‡Department of Microbiology and Immunology.
authors: Meghan E
authors: ME
authors: Feltcher
authors: §Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, North Carolina, 27599;
authors: Harsha P
authors: HP
authors: Gunawardena
authors: From the ‡Department of Microbiology and Immunology.
authors: Katelyn E
authors: KE
authors: Zulauf
authors: From the ‡Department of Microbiology and Immunology.
authors: Seidu
authors: S
authors: Malik
authors: ¶Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts 01655;
authors: Jennifer E
authors: JE
authors: Griffin
authors: ¶Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts 01655; ‖Howard Hughes Medical Institute, Chevy Chase, Maryland, 20815.
authors: Christopher M
authors: CM
authors: Sassetti
authors: §Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, North Carolina, 27599; braunstein@med.unc.edu xchen@email.unc.edu.
authors: Xian
authors: X
authors: Chen
authors: From the ‡Department of Microbiology and Immunology, braunstein@med.unc.edu xchen@email.unc.edu.
authors: Miriam
authors: M
authors: Braunstein
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D040901:Proteomics
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C510664:Mce4A protein, Mycobacterium tuberculosis; D026901:Membrane Transport Proteins; C473802:mammalian cell entry protein Mce1A, Mycobacterium tuberculosis; D000251:Adenosine Triphosphatases; C442123:SecA2 protein, Mycobacterium