EspB and EspD require a specific chaperone for proper secretion from enteropathogenic Escherichia coli

Area of Science:

• Microbiology
• Molecular Biology
• Pathogenesis

Background:

• Enteropathogenic Escherichia coli (EPEC) employs a type III secretion system (T3SS) to translocate effector proteins into host epithelial cells.
• Key secreted proteins like EspA, EspB, and EspD are critical for EPEC virulence.

Purpose of the Study:

• To identify and characterize novel proteins involved in the T3SS-mediated secretion pathway of EPEC.
• To investigate the role of the newly identified protein, CesD, in the secretion of Esp proteins and its contribution to pathogenesis.

Main Methods:

• Genetic mutation analysis of the cesD gene in EPEC.
• Detection and quantification of secreted proteins (EspA, EspB, EspD) in culture supernatants using protein assays.
• Assessment of host cell interactions, including FAS and Tir phosphorylation.
• Co-immunoprecipitation assays to determine protein-protein interactions.
• Subcellular localization studies of CesD within bacterial cells.

Main Results:

• A cesD mutation abolished EspD secretion and reduced EspB secretion, while EspA secretion remained largely unaffected.
• The cesD mutant exhibited defects in FAS and Tir phosphorylation, indicating impaired virulence.
• CesD was found to interact specifically with EspD.
• CesD localized to both the bacterial cytosol and the inner membrane.

Conclusions:

• CesD functions as a secretion chaperone essential for the proper export of EspB and EspD in EPEC.
• CesD's unique localization to the inner membrane distinguishes it from previously characterized T3SS chaperones.
• CesD plays a significant role in EPEC pathogenesis by facilitating the secretion of key virulence factors.