Atomic structures of a bacteriocin targeting Gram-positive bacteria

Area of Science:

• Structural Biology
• Microbiology
• Biochemistry

Background:

• Contractile nanomachines are potent antibacterial agents, but their structures are primarily known for targeting Gram-negative bacteria.
• Understanding structural differences is crucial for engineering nanomachines effective against Gram-positive bacteria, which possess distinct cell envelopes.

Purpose of the Study:

• To determine the atomic structures of an engineered diffocin, a contractile nanomachin designed to kill the Gram-positive bacterium *Clostridioides difficile*.
• To elucidate the structural basis for diffocin function and compare it with nanomachines targeting Gram-negative bacteria.

Main Methods:

• X-ray crystallography was used to capture the diffocin in pre- and post-contraction states.
• Cryo-electron microscopy and structural analysis were employed to resolve atomic details.

Main Results:

• The atomic structures of the engineered diffocin were determined in three states, revealing its components: a baseplate, trunk, collar, and tube.
• Significant structural differences were observed in the baseplate and contraction magnitude compared to nanomachines targeting Gram-negative bacteria.
• The multifunctional hub-hydrolase protein and tape measure protein were characterized, providing insights into the mechanism of peptidoglycan degradation during bacterial cell wall penetration.

Conclusions:

• The study provides atomic-level structural insights into a novel protein antibiotic targeting Gram-positive bacteria.
• The findings highlight key mechanical principles and structural differences relevant for designing advanced, precision protein-based antibiotics.
• This work lays the foundation for developing new therapeutic strategies against Gram-positive bacterial pathogens.