VP15R from infectious spleen and kidney necrosis virus is a non-muscle myosin-II-binding protein

VP15R protein, encoded by the 15th open reading frame of infectious spleen and kidney necrosis virus (ISKNV), was identified. VP15R is a 263-residue protein that is first transcribed within 12 h post-infection. The VP15R mRNA is transcribed beginning at ISKNV genomic coordinate 12111, extending 167 bp upstream of the initiation codon. No signal peptides, transmembrane fragments, or nuclear localization signal sequences were predicted in the VP15R sequence. The 102–202 sequence of VP15R is homologous to the 1153–1253 sequence of the filamin C protein of Danio rerio (zebrafish), with an identity of 29%. Immunofluorescence and VP15R-GFP fusion protein subcellular localization assays showed that VP15R is localized in the cytoplasm. Pull-down and MALDI-TOF–TOF/MS assays demonstrated that VP15R can bind to the non-muscle myosin II (NM II) protein. Co-immunoprecipitation assays confirmed that VP15R can bind to the heavy chains of the NM II protein of mandarin fish, mice, and humans.