Phage lysis protein Lys^M acts as a wedge to block MurJ conformational changes

Area of Science:

• Microbiology
• Structural Biology
• Drug Discovery

Background:

• Multidrug-resistant bacteria pose a significant global health threat, necessitating novel antibacterial strategies.
• The peptidoglycan biogenesis pathway is essential for bacterial survival, with MurJ (lipid II flippase) being a critical membrane protein in *Escherichia coli*.
• The phage protein Lys^M (Sgl^M) targets MurJ to induce cell lysis, but its mechanism is unknown.

Purpose of the Study:

• To elucidate the molecular mechanism by which the phage protein Lys^M inhibits the essential bacterial enzyme MurJ.
• To determine the structural basis for Lys^M's interaction with MurJ.
• To provide a foundation for designing new antimicrobial agents targeting MurJ.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structure of the MurJ/Lys^M complex.
• Alanine-scanning mutagenesis and pull-down assays were employed to identify key functional residues.
• Molecular dynamics simulations were performed to analyze the stabilization of MurJ's conformation.

Main Results:

• The cryo-EM structure revealed Lys^M wedges between TM2 and TM7 of MurJ, locking it in an outward-facing conformation.
• Key residues involved in Lys^M's function were identified through mutagenesis and biochemical assays.
• Molecular dynamics simulations confirmed that Lys^M stabilizes the outward-facing state of MurJ, blocking lipid II transport.

Conclusions:

• Lys^M employs an unprecedented mechanism to inhibit MurJ by acting as a wedge, stabilizing an outward-facing conformation.
• This structural insight provides a framework for developing novel MurJ-targeted antimicrobial agents to combat resistant bacteria.