# Substrate Specificity and Immunological Implications of Cutibacterium acnes Phage Endolysins

## TL;DR

This study explores how phage endolysins from Cutibacterium acnes can target bacterial cell walls and potentially influence immune responses, offering a new approach to treating antibiotic-resistant acne.

## Contribution

The paper introduces a classification of endolysins based on substrate-binding preferences and suggests their potential immunomodulatory functions.

## Key findings

- Endolysins CAP 6-3, 7-1, and 12-3 showed higher affinity for NAG–NAM dimers, while CAP 1-1 and CAP 10-3 preferred MDP.
- Conserved histidine and ASP170 residues were identified as important for substrate interactions.
- MDP binding may influence host immune responses via NOD2 signaling.

## Abstract

Cutibacterium acnes resistance to antibiotics poses a significant challenge in treating acne vulgaris. Bacteriophages offer a promising alternative to overcome this challenge given their specificity. In the current study, 15 bacteriophages were isolated from acne affected volunteers and subjected to whole genome sequencing to characterize their genetic features, diversity and endolysins encoding genes for further structural and functional analysis. Five representative endolysins (CAP 1-1, 6-3, 7-1, 10-3, and 12-3) were chosen for structural and functional analysis after average nucleotide identity (ANI) analysis where 5 different endolysins were categorized. Furthermore, molecular docking studies assessed the binding affinities of endolysins to common peptidoglycan fragments of C. acnes cell wall, identifying variations in the binding interactions as CAP 6-3, 7-1, and 12-3 had greater affinities for the NAG–NAM dimer, while CAP 1-1 and CAP 10-3 interacted preferentially with NAM-L-alanyl-D-isoglutamine (MDP). Residue-level interaction mapping revealed several conserved histidine residues; ASP170 is conserved in peptide-targeting endolysins. These results imply that C. acnes phage (CAP) endolysins may be functionally differentiated into peptide-targeting and glycan-targeting classes based on their substrate-binding preferences, in addition to the traditional classification of endolysins by bond-cleaving activity. Notably, by interfering with NOD2-mediated signaling, MDP binding may increase the potential for modifying host immunological responses. Together, this research offers novel molecular understandings of the substrate selectivity and possible immunomodulatory functions of CAP phage endolysins. These results provide computational insights into substrate specificity and potential immunomodulatory mechanisms of C. acnes phage endolysins therefore experimental validation is necessary to verify their biological and therapeutic significance.