<i>Escherichia coli</i> phage ΦPNJ-9 adheres to mucus via a variant Hoc protein

Phages, as antagonists of bacteria, hold significant promise for combating drug-resistant bacterial infections. Their host specificity allows phages to target pathogenic bacteria without disrupting the gut microbiota, offering distinct advantages in the prevention and control of intestinal pathogens. The interaction between the phage and the gut plays a crucial role in the efficacy of phage-mediated bacterial killing. However, the mechanisms underlying these interactions remain poorly understood. In this study, we demonstrate that the clinically isolated T4-like phage, ΦPNJ-9, effectively adheres to the intestinal mucosa <i>in vivo</i>. This adhesion is mediated by the phage's Hoc protein, which interacts with MUC2 in the mucus. The Hoc protein of ΦPNJ-9 represents a variant, consisting of only three domains and lacking Domain 3, in contrast to phage T4. The key interacting sites on ΦPNJ-9 Hoc are amino acids S183, L184, and T185 within Domain 2. Displaying Domain 2 of ΦPNJ-9 Hoc on the surface of M13 phage significantly enhances its adhesion to the intestinal mucosa. Additionally, we identify fucose residues in MUC2 as the critical binding sites for the phage. Through this adhesion, the phage occupies the intestinal niche, thereby protecting the mucosal layer from pathogenic <i>Escherichia coli</i> infections. Our findings highlight the role of Hoc proteins in phage adhesion to intestinal mucus and the variation in binding sites, providing key insights for phage-based strategies aimed at preventing and controlling intestinal pathogens.IMPORTANCEThe rise in antibiotic-resistant pathogenic bacteria has sparked renewed interest in phage therapy as a promising alternative, particularly for targeting intestinal pathogens due to phage's host specificity. However, clinical applications have revealed that many phages are ineffective in eliminating bacteria within the gut, primarily due to the complex interactions between the phage and the gut environment. However, the mechanisms underlying these interactions remain poorly understood. Our previous study demonstrated that a T4-like phage adheres to the intestinal mucosa through the interaction between its Hoc protein and MUC2 in the mucus. Whether this model is widespread among T4-like phages remains unknown. Here, we characterize a variant Hoc protein from a T4-like phage, and identify new binding sites within this protein. Our findings suggest that the interaction between Hoc and MUC2 is likely common, but the critical binding sites vary depending on the specific phage.