Translocation of surface-localized effectors in type III secretion

Area of Science:

• Microbiology
• Immunology
• Molecular Biology

Background:

• Pathogenic Yersinia species evade host immunity using a plasmid-encoded type III secretion system (T3SS).
• The T3SS is known to translocate effector proteins into host cells, suppressing immune responses.
• Current models propose a single-step translocation from the bacterial cytosol to the host cell cytoplasm.

Purpose of the Study:

• To investigate the translocation mechanism of Yersinia type III secretion system (T3SS) substrates.
• To determine if T3SS substrates on the bacterial surface can be translocated into host cells.
• To challenge the existing single-step conduit model of T3SS-mediated protein translocation.

Main Methods:

• Utilized Yersinia pseudotuberculosis and purified YopH.
• Coated Y. pseudotuberculosis with purified YopH and observed translocation upon host cell contact.
• Tested translocation of externally added YopH using functional T3SS and specific effector domains.
• Employed coated Salmonella typhimurium strains to assess conserved T3SS translocation mechanisms.

Main Results:

• Purified YopH, when coated on Y. pseudotuberculosis, was translocated into target cells upon contact, inducing a physiological response.
• Translocation of externally added YopH required a functional T3SS and a specific translocation domain.
• Efficient, T3SS-dependent translocation of extracellular YopH was demonstrated in vitro using coated S. typhimurium, indicating conserved mechanisms.

Conclusions:

• Yersinia T3SS can translocate effector proteins that are already on the bacterial surface or added extracellularly.
• This suggests an intermediate extracellular step in T3SS-mediated protein translocation, distinct from the single-step conduit model.
• The findings highlight a conserved mechanism for T3SS-dependent translocation of extracellular effector proteins among pathogens.