Microbiology
Structure of the Mycosin-1 Protease from the Mycobacterial ESX-1 Protein Type VII Secretion System*

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Mycobacteria use specialized type VII (ESX) secretion systems to export proteins across their complex cell walls. Mycobacterium tuberculosis encodes five nonredundant ESX secretion systems, with ESX-1 being particularly important to disease progression. All ESX loci encode extracellular membrane-bound proteases called mycosins (MycP) that are essential to secretion and have been shown to be involved in processing of type VII-exported proteins. Here, we report the first x-ray crystallographic structure of MycP1(24–407) to 1.86 Å, defining a subtilisin-like fold with a unique N-terminal extension previously proposed to function as a propeptide for regulation of enzyme activity. The structure reveals that this N-terminal extension shows no structural similarity to previously characterized protease propeptides and instead wraps intimately around the catalytic domain where, tethered by a disulfide bond, it forms additional interactions with a unique extended loop that protrudes from the catalytic core. We also show MycP1 cleaves the ESX-1 secreted protein EspB from both M. tuberculosis and Mycobacterium smegmatis at a homologous cut site in vitro.

Background: The mycosin-1 protease (MycP1) is essential for export and cleavage of the type VII-secreted virulence-associated proteins involved in pathogenesis of Mycobacterium tuberculosis and related species.

Results: The x-ray structure of MycP1, with its proposed propeptide, is described.

Conclusion: The proposed propeptide wraps around the perimeter of a subtilisin-like fold, leaving the catalytic center unobstructed.

Significance: MycP1 may operate through a novel mode of regulation.

Microbiology
Mycobacteria
Mycobacterium tuberculosis
Protease
Protein Secretion
ESX
Subtilisin
Type VII Secretion System

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The atomic coordinates and structure factors (codes 4J94 and 4KPG) have been deposited in the Protein Data Bank (http://wwpdb.org/).

*

This work was supported in part by operating grants from the Canadian Institute of Health Research and the Howard Hughes Medical Institute International Senior Scholar Program.

1

Supported by a University of British Columbia 4-year Ph.D. fellowship.