Structure of a bacterial type IV secretion core complex at subnanometre resolution

Area of Science:

• Bacterial molecular biology
• Structural biology
• Microbial pathogenesis

Background:

• Type IV secretion (T4S) systems are crucial for transporting DNA and proteins across bacterial membranes.
• These systems form large, 12-protein complexes (VirB1-11 and VirD4) with a core complex (CC) spanning bacterial membranes.
• The outer membrane (O-layer) structure is known, but the inner membrane (I-layer) structure remains uncharacterized.

Purpose of the Study:

• To determine the high-resolution structure of the I-layer of the T4S core complex.
• To elucidate the arrangement and location of I-layer components within the bacterial inner membrane.
• To gain structural insights into the overall T4S system mechanism.

Main Methods:

• High-resolution cryo-electron microscopy (cryo-EM) was employed to visualize the I-layer.
• Molecular modeling techniques were used to interpret the cryo-EM data.
• Biochemical approaches were integrated to validate structural findings and component localization.

Main Results:

• The detailed three-dimensional structure of the T4S system's I-layer was successfully determined.
• The precise locations of individual protein components within the I-layer were identified in the electron density map.
• This structural information provides a more complete picture of the membrane-spanning core complex.

Conclusions:

• The determined I-layer structure significantly advances our understanding of T4S system architecture.
• These findings provide essential structural insights for deriving the functional mechanisms of T4S systems.
• This work lays the foundation for future studies on T4S system assembly and substrate translocation.