The Leader of the Capsid protein from Feline calicivirus must be palmitoylated and form oligomers through disulfide bonds for efficient viral replication

Feline calicivirus (FCV), a member of the Vesivirus genus and a model for studying of the members of the Caliciviridae, has been used to understand the biology and viral replication of etiological agents of medical and veterinary importance. The leader of the capsid (LC) protein is exclusive to the Vesivirus genus members whose importance for a successful viral replication has been demonstrated; however, its cell localization, post-translational modifications, and specific functions throughout the viral replication cycle are poorly understood. We have determined that the expression of the LC protein from FCV in a virus-free system is located at the mitochondria and induces apoptosis; furthermore, the in vitro characterization of a purified LC protein showed that it has viroporin characteristics. Here, using an LC-reactive serum, the LC protein expression kinetics, cellular localization, post-translational modifications, and association with cellular PDI proteins in FCV infected cells was determined. We found that the LC protein is present on the membrane of infected cells and in the supernatants, independently of cell lysis, which suggests that it is actively secreted. Moreover, we found that LC protein is palmitoylated during infection and that palmitoylation inhibition alters its levels and subcellular localization. Finally, we determined that the LC protein forms oligomers dependent on disulfide bonds mediated by PDI activity. In addition, it interacts with PDIA3, a disulfide isomerase known as an important factor in the replication of several viruses. The results indicate that the LC protein from FCV might have multiple roles during FCV replication. IMPORTANCEFeline calicivirus (FCV) is a highly transmissible virus that represents a significant cause of upper respiratory infection in domestic and wild cats worldwide. FCV also serves as one of the most valuable models for studying calicivirus biology, as unlike most members of the family, known to cause diseases in animals and humans, it can be easily grown in cell culture. Since there are no efficacious vaccines or antivirals against most caliciviruses, studying their molecular biology and the relationship between viral and cellular components is essential for developing strategies for their prevention and control.