Pathogen hijacks focal adhesion signaling by a T3SS effector CteX

Area of Science:

• Microbiology
• Molecular Biology
• Structural Biology

Background:

• Gram-negative bacterial infections often utilize type III secretion system (T3SS) effectors.
• The opportunistic pathogen Chromobacterium violaceum possesses a T3SS (Cpi-1/-1a), but its effector proteins are not fully characterized.

Purpose of the Study:

• To comprehensively identify and functionally characterize novel T3SS effectors from C. violaceum.
• To elucidate the mechanism and role of a newly discovered effector in bacterial pathogenesis.

Main Methods:

• Proteomic analysis of the C. violaceum T3SS secretome.
• Structural determination of the novel effector CteX.
• In vitro functional assays to determine CteX enzymatic activity and substrate specificity.
• Cell-based assays to assess effects on host cell cytoskeleton and focal adhesions.
• Animal infection models to evaluate CteX's role in virulence and colonization.

Main Results:

• A novel T3SS effector, CteX, was identified in C. violaceum.
• CteX was structurally determined to possess a papain-like fold and functions as a cysteine protease.
• CteX specifically cleaves the host focal adhesion protein Paxillinα, leading to focal adhesion collapse and actin cytoskeleton remodeling.
• CteX-mediated cytoskeletal changes limit excessive epithelial cell invasion by C. violaceum.
• CteX is essential for C. violaceum virulence and sustained colonization in animal models.

Conclusions:

• CteX is a novel T3SS effector from C. violaceum that targets host Paxillinα.
• CteX regulates bacterial persistence and virulence by modulating host cell structure and limiting host cell damage.
• This study reveals an unexpected mechanism of bacterial pathogenesis involving protease-mediated disruption of host focal adhesions.