Dissection of the TssB-TssC interface during type VI secretion sheath complex formation

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• The Type VI secretion system (T6SS) is a complex molecular machine involved in interbacterial and host-pathogen interactions.
• The T6SS utilizes a contractile phage-tail-like structure to deliver effector proteins, including toxins, into target cells.
• The T6SS sheath, composed of TssB and TssC proteins, is essential for the system's contractile mechanism.

Purpose of the Study:

• To investigate the molecular interactions between TssB and TssC proteins in enteroaggregative E. coli.
• To identify the specific protein domains and residues involved in the TssB-TssC interaction.
• To elucidate the role of this interaction in T6SS sheath assembly and function.

Main Methods:

• Confirmation of TssB-TssC interaction using techniques in enteroaggregative E. coli.
• Site-directed mutagenesis to probe the roles of specific TssB and TssC regions.
• Phenotypic analyses to assess the impact of mutations on T6SS assembly and function.

Main Results:

• The interaction between TssB and TssC was confirmed in enteroaggregative E. coli.
• The N-terminal region of TssC and a conserved α-helix of TssB are required for their interaction.
• An hydrophobic motif within the TssB α-helix is critical for TssB-TssC binding, sheath assembly, and T6SS activity.

Conclusions:

• Specific molecular interactions between TssB and TssC are essential for T6SS assembly and function.
• The identified hydrophobic motif in TssB plays a critical role in mediating the TssB-TssC interaction and subsequent T6SS activity.
• These findings provide detailed insights into the structural requirements for T6SS sheath formation and function.