The E. coli effector protein NleF is a caspase inhibitor

Area of Science:

• Microbiology
• Cell Biology
• Structural Biology

Background:

• Enterohemorrhagic and enteropathogenic E. coli (EHEC/EPEC) cause severe infections via effector proteins.
• The function of many virulence-associated effector proteins remains unknown.
• Apoptosis evasion is a key bacterial virulence strategy.

Purpose of the Study:

• To elucidate the molecular function of the E. coli effector protein NleF.
• To investigate NleF's interaction with host cell death pathways.
• To determine the structural basis for NleF's mechanism of action.

Main Methods:

• Yeast two-hybrid, LUMIER, and direct interaction assays to study protein binding.
• In vitro and cell lysate assays to assess caspase inhibition.
• Crystal structure determination of the caspase-9/NleF complex.
• Mutagenesis studies to validate the structural model.

Main Results:

• NleF directly binds to caspases-4, -8, and -9.
• NleF inhibits caspase activity and prevents apoptosis in human cell lines.
• The crystal structure reveals NleF's unique inhibitory mode via its C-terminus.
• Mutations in NleF's C-terminus abolish caspase binding and apoptosis inhibition.

Conclusions:

• NleF is a novel bacterial effector that directly inhibits caspases, thereby preventing apoptosis.
• NleF employs a unique mechanism of caspase inhibition distinct from known inhibitors.
• This study reveals a new strategy used by pathogenic E. coli to subvert host defenses and promote infection.