Type III secretion translocon assemblies that attenuate Yersinia virulence

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Type III secretion systems (T3SS) are crucial virulence factors for many bacterial pathogens.
• T3SS translocate bacterial effector proteins into host cells, disrupting cellular functions.
• The Yersinia YopB-YopD translocon forms a pore in the host membrane for effector entry.

Purpose of the Study:

• To investigate the role of the C-terminal α-helix motif of Yersinia YopD in translocon function and bacterial virulence.
• To determine if YopD mutations affecting translocon pore formation impact effector translocation and pathogenicity.

Main Methods:

• Site-directed mutagenesis was used to create four YopD variants with mutations in a predicted C-terminal α-helix.
• Bacterial effector translocation into eukaryotic cells was assessed in vitro.
• Translocon pore formation and stability were analyzed using erythrocyte lysis assays.
• The virulence of Yersinia strains expressing mutant YopD proteins was evaluated in a mouse infection model.

Main Results:

• Mutants YopD(I262P) and YopD(K267P) exhibited defects in effector translocation and host cell membrane insertion, leading to impaired virulence.
• Mutants YopDA(263P) and YopD(A270P) formed smaller translocon pores but showed no significant in vitro translocation defect.
• All four YopD mutants were attenuated in the mouse infection model, indicating reduced pathogenicity.
• Despite in vitro translocon activity, mutant YopD variants failed to confer lethal effects in vivo.

Conclusions:

• The C-terminus of YopD plays a critical role in the proper assembly and function of the YopB-YopD translocon.
• YopD variants can form functional translocon pores for effector delivery in vitro but may require additional functions for full virulence in vivo.
• Bacterial translocators may possess functions beyond simple effector delivery, contributing to pathogenesis in ways not yet fully understood.