N123I mutation in the ALV-J receptor-binding domain region enhances viral replication ability by increasing the binding affinity with chNHE1

The subgroup J avian leukosis virus (ALV-J), a retrovirus, uses its gp85 protein to bind to the receptor, the chicken sodium hydrogen exchanger isoform 1 (chNHE1), facilitating viral invasion. ALV-J is the main epidemic subgroup and shows noteworthy mutations within the receptor-binding domain (RBD) region of gp85, especially in ALV-J layer strains in China. However, the implications of these mutations on viral replication and transmission remain elusive. In this study, the ALV-J layer strain JL08CH3-1 exhibited a more robust replication ability than the prototype strain HPRS103, which is related to variations in the gp85 protein. Notably, the gp85 of JL08CH3-1 demonstrated a heightened binding capacity to chNHE1 compared to HPRS103-gp85 binding. Furthermore, we showed that the specific N123I mutation within gp85 contributed to the enhanced binding capacity of the gp85 protein to chNHE1. Structural analysis indicated that the N123I mutation primarily enhanced the stability of gp85, expanded the interaction interface, and increased the number of hydrogen bonds at the interaction interface to increase the binding capacity between gp85 and chNHE1. We found that the N123I mutation not only improved the viral replication ability of ALV-J but also promoted viral shedding in vivo. These comprehensive data underscore the notion that the N123I mutation increases receptor binding and intensifies viral replication. Attachment is a critical initial step in retroviral infections. The RBD of gp85 in ALV-J is critical for binding to the cell membrane receptor, chNHE1. This investigation establishes a strong link between the heightened replication ability of the layer strain JL08CH3-1 and the enhanced binding capacity exhibited by gp85 toward chNHE1 compared to the prototype strain HPRS103. We found for the first time that the N123I mutation within the RBD region of gp85 increased the binding capacity between gp85 and chNHE1 and enhanced the replication ability of ALV-J. Our results provide important information on the implications of mutations within the RBD region of gp85 and highlight the importance of monitoring variations in the RBD region of ALV-J to prevent future outbreaks.