Feline infectious peritonitis (FIP) is a critical and lethal disease affecting cats, caused by the Feline infectious peritonitis virus (FIPV), which has five accessory genes, including 7b. This study is the first to examine the expression, processing, glycosylation, and subcellular localization of the 7b protein in FIPV-infected cells. Key findings include the generation of a recombinant FIPV expressing a non-glycosylated 7b protein, which was shown to co-localize with the Golgi apparatus and not be secreted. Additionally, rFIPVs expressing flag-tagged 7b proteins were created to analyze the mature, glycosylated form, revealing that this form is also retained in the medial/trans Golgi. The study further investigated the C-terminal KTEL motif of the 7b protein, demonstrating that only the intact KTEL motif maintains Golgi retention. Alterations to this motif, such as KDEL, led to ER retention, while other modifications resulted in efficient secretion of the protein. These results provide crucial insights into the 7b protein's role and its Golgi retention signal in FIPV-infected cells, highlighting the need for further research to clarify its function in the coronaviral life cycle.
