The Structure and Function of Biomaterial Endolysin EFm1 from E. faecalis Phage

Area of Science:

• Microbiology
• Structural Biology
• Biotechnology

Background:

• *Enterococcus faecalis* is a significant Gram-positive pathogen causing severe human health threats.
• Bacteriophages and their encoded enzymes, like endolysins, are explored as alternatives to antibiotics.
• Endolysin EFm1 from phage IME-EF1 shows promise in targeting *E. faecalis*.

Purpose of the Study:

• To investigate the structure and lytic activity of endolysin EFm1 against *E. faecalis*.
• To identify key domains and residues responsible for EFm1's lytic function.
• To evaluate the therapeutic potential of EFm1 as a biomaterial.

Main Methods:

• Structural analysis of EFm1 variants (EFm1_D166Q and EFm1_{166-237 aa}) using techniques like X-ray crystallography.
• Lytic activity assays against various *E. faecalis* strains.
• In vivo expression studies and gene knockdown experiments.

Main Results:

• EFm1 demonstrated specific lytic activity against most tested *E. faecalis* strains, but not *E. faecalis* 945.
• Structural analysis revealed EFm1 forms tetrameric and octameric structures, identifying crucial domains: calcium-binding sites, a catalytic triad, tetramerization sites, and ion channel regions.
• EFm1 showed limited activity when expressed alone in vivo, and its absence impacted phage IME-EF1 lytic activity.

Conclusions:

• EFm1 possesses specific lytic activity against *E. faecalis*, highlighting its potential as a targeted antibacterial agent.
• Understanding EFm1's structure-function relationship provides insights into its mechanism of action.
• EFm1 represents a promising biomaterial for combating diseases caused by the opportunistic pathogen *E. faecalis*.