Palmitoylation of the hemagglutinin of influenza B virus by ER-localized DHHC enzymes 1, 2, 4, and 6 is required for efficient virus replication

Covalent attachment of the fatty acid palmitate or stearate to the cytoplasmic domain of viral glycoproteins is often crucial for viral replication. This has previously been studied for the hemagglutinin (HA) of influenza A virus and the responsible enzymes have been identified, but similar studies have not been performed with HA of influenza B virus, which contains palmitate linked to two cysteines. We show here that the modification is required for efficient virus replication since exchange of both cysteines or the cysteine located at the end of the cytoplasmic tail prevented the generation of viable viruses. Viruses with an exchange of the membrane-proximal cysteine rapidly reverted back to wild-type virus. Blocking exit of proteins from the endoplasmic reticulum (ER) revealed that palmitoylation of HA of influenza B virus occurs in the ER, whereas acylation of HA of influenza A virus occurs in the Golgi. Infecting cells deficient in Asp-His-His-Cys (DHHC) palmitoyltransferases revealed that HA of influenza B virus is acylated by the ER-localized DHHCs 1, 2, 4, and 6, which are thus different from the enzymes previously identified for acylation of HA of influenza A virus. A comparison of predicted and experimentally determined protein structures suggests that the exclusive acylation of the HA of influenza B virus with palmitate is not a function of the responsible DHHCs and that the transmembrane region may be critical for the acylation of HA of influenza A and B viruses by different DHHCs.

Automated summary

This study found that the palmitoylation of HA of influenza B virus occurs in the ER, whereas acylation of HA of influenza A virus occurs in the Golgi. The ER-localized DHHCs 1, 2, 4, and 6 are responsible for acylation of HA of influenza B virus, which is different from the enzymes identified for acylation of HA of influenza A virus. The transmembrane region may be critical for the acylation of HA of influenza A and B viruses by different DHHCs.