Apolipoprotein mediates soft-shelled turtle systemic septicemia spherical virus (STSSSV) infection

Soft-shelled turtle systemic septicemia spherical virus (STSSSV) is a devastating pathogen of farmed Pelodiscus sinensis and causes great economic losses. Little is known about the pathogenic mechanisms of this virus. In this study, STSSSV was found to bind three proteins with molecular masses of approximately 260, 212 and 134 kDa from the turtle P. sinensis via overlay assays. A matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis revealed that the 260 kDa protein shared the closest homology with apolipoprotein B (ApoB). A blotting assay showed that anti-mouse ApoB antibody cross-reacted with the P. sinensis apolipoprotein B (PApoB) protein. A high interaction affinity between PApoB and STSSSV was confirmed by co-immunoprecipitation. In an immunofluorescence assay, PApoB colocalized with STSSSV both on the surfaces of and within turtle cells. Moreover, the ApoB antibody was able to inhibit STSSSV infection. These data suggest that PApoB mediates the infection of P. sinensis by STSSSV.