The T3SS Effector Protease NleC Is Active within Citrobacter rodentium

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Gram-negative bacterial pathogens utilize type III secretion systems (T3SS) to inject effector proteins into host cells.
• Traditionally, T3SS effectors are believed to be inactive until translocated into the host cell.
• Previous work demonstrated intra-bacterial activity of T3SS effectors NleB and SseK1 in modifying bacterial proteins.

Purpose of the Study:

• To investigate the intra-bacterial activity of the T3SS effector protease NleC.
• To determine if NleC is enzymatically active within the bacterium *Citrobacter rodentium*.

Main Methods:

• Expression of the NF-κB p65 subunit, a known substrate of NleC, within *C. rodentium*.
• Monitoring proteolytic cleavage of p65 as an indicator of NleC activity.
• Utilizing a p65 mutant lacking the NleC cleavage motif to assess specificity.

Main Results:

• Proteolytic cleavage of the NF-κB p65 subunit was observed within *C. rodentium*.
• This intra-bacterial cleavage was strictly dependent on the presence of NleC.
• A mutant p65 lacking the NleC cleavage motif was resistant to cleavage, confirming NleC's action.

Conclusions:

• The type III secretion system effector protease NleC exhibits enzymatic activity within *C. rodentium*.
• This finding extends the understanding of intra-bacterial roles for T3SS effectors.
• NleC joins NleB as a T3SS effector with demonstrated activity prior to host cell injection.