Salmonella InvG forms a ring-like multimer that requires the InvH lipoprotein for outer membrane localization

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• Salmonella species inject virulence effector proteins into host cells via a type III secretion apparatus (SPI-1).
• The assembly and structure of this secretion apparatus are not well understood.
• The InvG protein is crucial for this secretion and may form the outer membrane channel.

Purpose of the Study:

• To investigate the role of InvH in the assembly and localization of the InvG protein.
• To characterize the structure of the InvG protein.

Main Methods:

• Co-expression of InvG and InvH in recombinant Escherichia coli.
• Mutation of the invH gene in Salmonella typhimurium.
• SDS-PAGE to assess protein multimerization.
• Extracellular protease accessibility assays.
• Electron microscopy of purified InvG.

Main Results:

• InvH co-expression enhanced InvG yield in E. coli.
• invH mutation reduced InvG levels in S. typhimurium.
• InvG formed SDS-resistant multimers independently, but outer membrane localization required InvH.
• InvH, an outer membrane lipoprotein, mediated InvG targeting to the outer membrane.
• InvG targeted to the outer membrane by InvH was accessible to extracellular protease.
• InvG and InvH did not form a stable complex.
• Electron microscopy revealed InvG forms an oligomeric ring structure (7 nm inner, 15 nm outer diameter).

Conclusions:

• InvH is essential for the correct localization of InvG to the bacterial outer membrane.
• InvG forms a ring-like oligomeric structure, likely serving as the secretion channel for Salmonella effector proteins.
• This study elucidates key aspects of the type III secretion apparatus structure and assembly.