Structure of the enterococcal T4SS protein PrgL reveals unique dimerization interface in the VirB8 protein family

Area of Science:

• Microbiology
• Structural Biology
• Molecular Biology

Background:

• Multidrug-resistant bacteria are a significant cause of hospital-acquired infections (HAIs).
• Conjugative gene transfer, mediated by type 4 secretion systems (T4SS), is a primary mechanism for antibiotic resistance spread.
• While Gram-positive bacteria, particularly enterococci, are major contributors to HAIs, their T4SSs are less characterized than those of Gram-negative bacteria.

Purpose of the Study:

• To elucidate the structure and organization of PrgL, a core protein of the T4SS channel from the Gram-positive bacterium Enterococcus faecalis.
• To compare the structural features of PrgL with VirB8 proteins from Gram-negative T4SSs.
• To investigate the functional significance of PrgL dimerization in vivo.

Main Methods:

• X-ray crystallography to determine the structure of the PrgL protein.
• In vitro biochemical assays to assess protein dimerization and oligomerization.
• In vivo genetic experiments to confirm the importance of PrgL dimerization for T4SS function.

Main Results:

• The structure of PrgL was determined, revealing similarities to VirB8 proteins found in Gram-negative T4SSs.
• In vitro studies demonstrated that the soluble domain of PrgL can independently drive dimerization and dodecamerization.
• A unique dimerization interface for PrgL was identified, distinct from other known VirB8-like proteins.
• In vivo experiments confirmed the essential role of PrgL dimerization for T4SS function.

Conclusions:

• PrgL is a core component of Gram-positive T4SS, sharing structural homology with Gram-negative VirB8 proteins.
• PrgL possesses unique dimerization properties crucial for its function in conjugation.
• These findings offer insights into the molecular architecture of Gram-positive T4SS, highlighting conserved and novel features.