Three-Dimensional Structure Of Mud Crab Dicistrovirus

Mud crab(Scylla paramamosain) is an important breed of aquaculture. A dicistrovirus discovered in Mud crab, named as Mud crab dicistrovirus(MCDV), can cause “sleeping disease”, and trigger massive death of crabs and damage of aquaculture.In order to gain further understanding of MCDV and effective information of drug development, cryo-electron microscopy single particle method was applied to the study of three-dimensional structure of MCDV isolated from the sick crab. The results are listed hereafter:A three-dimensional structure of MCDV capsid was determined at 3.8 ?. The structure showed that the capsid was arranged in pseudo T=3 with 31 nm in diameter. At this resolution, the most secondary structures together with the large side chain densities can be easily identified.30 protrusions located around the two-fold axis with a diameter of about 4nm were found on the surface of MCDV capsid. Because of its flexible structure, we failed to get a resolution of the protrusion better than 10 ? of protrusions.A C_?model was firstly predicted based on the second structure of MCDV's coat proteins, VP1, VP2 and VP3, and then built according the densities of our map. According to the model, we found that the density of protrusion belongs to the dimer of VP2's C-terminal; There are 3 ?-strands of VP2's N-terminal, both of them can form special ?-sheets with other VP2 or VP3 by forming intermolecular hydrogen bond. These interactions can provide powerful stabilization to the capsid.In comparison with the same family members, CrPV and TrV, the obvious difference was found at 5-fold axis and some other places.Both heating and treating with EDTA can cause the MCDV to release the nucleic acid. The full and empty particles treated by heating were selected for the data processing independently. The results showed the protrusions around 2-fold axis were destroyed in empty particles while opposed to the full ones. That means heating can cause the protrusions broken and then result in the nucleic acid releasing.Based on our results, we propose a model for the invasion mechanism: Firstly, the protrusions can recognize and bind to the receptor of host, and cause the protrusions depolymerized and formed an ? helix binding to membrane, which can further bring about a pore in the membrane, and the 2-fold axis channel can also be opened after the protrusions conformation changed. All of these changes then result in the genome releasing.