Fish nodavirus causes the death of several high economic fish. For studying the package and stability of dragon grouper necrosis virus (DGNNV), wild type virus-like particles (wt-VLPs) and £GN25-VLPs were employed. After experiments of disassembly and assembly, the result showed that DNA of 608 bp was able to be packaged by wt-VLPs. The sedimentation of VLPs was affected by different pH buffers during the process of purification: the VLPs at alkaline conditions behaved faster than those at the acidic. The stability of pure VLPs was pH-independent. The micrographs of the wt-VLPs in alkaline buffers showed that particles were rough and irregular in shapes, some of which were stain-permeable. However, the wt-VLPs in acidic buffers were morphologically indistinguishable from the untreated VLPs. The Western blotting for gradiently purified miture of VLPs and lysozyme revealed that lysozyme was co-precipitated with wt-VLPs.

Dragon grouper nervous necrosis virus (DGNNV), a betanodavirus, is the causative agent of viral nervous necrosis (VNN) in dragon grouper (Epinephelus lanceolatus). In our study, capsid protein of DGNNV was expressed in Escherichia coli. We mutated arginines at N-termini capsid protein to investigate the role of arginines at 29-31th position. When capsid protein lost 25 amino acids at N-termini VLPs form, mutation in any two arginines at 29-31 position to alanine could the prohibit VLPs formation. Another extending three arginines at 23-25 position wouldn¡¦t increase the RNA encapsulation into VLPs. Furthermore, N-termini mutated VLPs were all RNase resistance like wt-VLPs, but the yield was distinctly less than wt-VLPs. In the single point alanine mutations, the VLPs yield of R29A was apparently higher than others (R30A and R31A). Using circular dichroism to observe the thermal denature process and thermal stability of DGNNV VLPs, we found the Tm about 60¢J of VLPs wouldn¡¦t alter even if arginines at 23-31 position were mutated. The findings suggested the VLPs of mutated arginines at 23-31 position wouldn¡¦t affect RNase resistance and thermal stability, but the yield were lower. Another, the arginines at the 30 and 31 position is more important than at 29 position for formation of VLPs.