Japanese encephalitis virus NS1′ protein depends on pseudoknot secondary structure and is cleaved by caspase during virus infection and cell apoptosis

Abstract

Japanese encephalitis virus (JEV) is a flavivirus with a complex life cycle involving mosquito vectors that mainly target birds and pigs, and causes severe encephalitis in children in Asia. Neurotropic flaviviruses of the JEV serogroup have a particular characteristic of expressing a unique nonstructural NS1′ protein, which is a prolongation of NS1 at the C terminus by 52 amino acids derived from a pseudoknot-driven-1 translation frameshift. Protein NS1′ is associated with virus neuro-invasiveness. In this study, the need of the pseudoknot structure for NS1′ synthesis was confirmed. By using a specific antibody against the prolonged peptide, NS1′ was found to be absent from the JEV SA14-14-2 vaccine strain, resulting from a single nucleotide silent mutation in the pseudoknot. A partial cleavage of NS1′ at a specific site of its C-terminal appendix recognized by caspases and inhibited by caspase inhibitors suggests a unique feature of intracellular NS1′.