Singapore Grouper Iridovirus ORF75R is a Scaffold Protein Essential for Viral Assembly.
Singapore Grouper Iridovirus (SGIV) is a member of nucleo cytoplasmic large DNA viruses (NCLDV). This paper reports the functional analysis of ORF75R, a major structural protein of SGIV. Immuno fluorescence studies showed that the protein was accumulated in the viral assembly site. Immunogold-labelling indicated that it was localized between the viral capsid shell and DNA core. Knockdown of ORF75R by morpholinos resulted in the reduction of coreshell thickness, the failure of DNA encapsidation, and the low yield of infectious particles. Comparative proteomics further identified the structural proteins affected by ORF75R knockdown. Two-dimensional gel electrophoresis combined with proteomics demonstrated that ORF75R was phosphorylated at multiple sites in SGIV-infected cell lysate and virions, but the vast majority of ORF75R in virions was the dephosphorylated isoform. A kinase assay showed that ORF75R could be phosphorylated in vitro by the SGIV structural protein ORF39L. Addition of ATP and Mg(2+) into purified virions prompted extensive phosphorylation of structural proteins and release of ORF75R from virions. These data suggest that ORF75R is a novel scaffold protein important for viral assembly and DNA encapsidation, but its phosphorylation facilitates virion disassembly. Compared to proteins from other viruses, we found that ORF75R shares common features with herpes simplex virus VP22.
Mechanobiology Institute, National University of Singapore, Singapore.
Fan
F
Wang
Mechanobiology Institute, National University of Singapore, Singapore.
Yang
Y
Liu
Department of Biological Sciences, National University of Singapore, Singapore.
Yi
Y
Zhu
Department of Biological Sciences, National University of Singapore, Singapore.
Bich
B
Ngoc Tran
Department of Biological Sciences, National University of Singapore, Singapore.
Jinlu
J
Wu
1] Mechanobiology Institute, National University of Singapore, Singapore [2] Department of Biological Sciences, National University of Singapore, Singapore.
Choy
C
Leong Hew
D000255:Adenosine Triphosphate / Q000494:pharmacology; D002213:Capsid / Q000187:drug effects / Q000378:metabolism; D055785:Gene Knockdown Techniques; D017994:Iridovirus / Q000187:drug effects / Q000472:pathogenicity / Q000502:physiology*; D008051:Lipid Bilayers / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D014764:Viral Proteins / Q000378:metabolism*; D014771:Virion / Q000187:drug effects / Q000378:metabolism; D019065:Virus Assembly / Q000187:drug effects; D014777:Virus Diseases / Q000378:metabolism
D008051:Lipid Bilayers; D014764:Viral Proteins; D000255:Adenosine Triphosphate; D008274:Magnesium