Native structure of a type IV secretion system core complex essential for Legionella pathogenesis

Area of Science:

• Microbiology
• Cell Biology
• Structural Biology

Background:

• Bacterial type IV secretion systems (T4SS) are crucial for pathogen virulence, enabling the delivery of effector proteins into host cells.
• Legionella pneumophila utilizes the Dot/Icm T4SS for intracellular survival and pathogenesis.
• Understanding the molecular architecture of T4SS is key to developing novel antimicrobial strategies.

Purpose of the Study:

• To determine the native molecular structure of the core complex of the Dot/Icm type IV secretion system from Legionella pneumophila.
• To elucidate the roles of key protein components in the assembly and function of the secretion machinery.

Main Methods:

• Transmission electron microscopy (TEM) was employed to visualize the native structure of the isolated Dot/Icm core complex.
• Biochemical isolation techniques were used to purify the core complex, comprising at least five proteins (DotC, DotD, DotF, DotG, and DotH).

Main Results:

• The core complex of the Dot/Icm T4SS exhibits a ring-shaped molecular structure.
• Distinct premature complexes were observed in the absence of DotG or DotF, suggesting sequential assembly steps.
• DotG appears to form a central channel spanning bacterial membranes, while DotF facilitates DotG integration into the complex.

Conclusions:

• The study provides unprecedented insights into the native structure and biogenesis of the Legionella Dot/Icm type IV secretion system.
• The findings reveal a potential common mechanism for the assembly of bacterial transport machinery.
• Elucidating the structural basis of T4SS function opens avenues for therapeutic interventions targeting bacterial infections.