Department of Medicine, Division of Infectious Diseases, University of California, San Francisco, San Francisco, United States; Chan-Zuckerberg Biohub, University of California, San Francisco, San Francisco, United States
Department of Medicine, Division of Infectious Diseases, University of California, San Francisco, San Francisco, United States; Chan-Zuckerberg Biohub, University of California, San Francisco, San Francisco, United States
Rachel Nakagawa
Department of Medicine, Division of Infectious Diseases, University of California, San Francisco, San Francisco, United States
Department of Medicine, Division of Infectious Diseases, University of California, San Francisco, San Francisco, United States; Chan-Zuckerberg Biohub, University of California, San Francisco, San Francisco, United States
Kenan C Murphy
Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, United States
Christopher M Sassetti
Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, United States
Department of Medicine, Division of Infectious Diseases, University of California, San Francisco, San Francisco, United States; Chan-Zuckerberg Biohub, University of California, San Francisco, San Francisco, United States
The ESX (or Type VII) secretion systems are protein export systems in mycobacteria and many Gram-positive bacteria that mediate a broad range of functions including virulence, conjugation, and metabolic regulation. These systems translocate folded dimers of WXG100-superfamily protein substrates across the cytoplasmic membrane. We report the cryo-electron microscopy structure of an ESX-3 system, purified using an epitope tag inserted with recombineering into the chromosome of the model organism Mycobacterium smegmatis. The structure reveals a stacked architecture that extends above and below the inner membrane of the bacterium. The ESX-3 protomer complex is assembled from a single copy of the EccB3, EccC3, and EccE3 and two copies of the EccD3 protein. In the structure, the protomers form a stable dimer that is consistent with assembly into a larger oligomer. The ESX-3 structure provides a framework for further study of these important bacterial transporters.
