Identification and characterization of a novel FstK-like protein from spotted knifejaw iridovirus (genus Megalocytivirus)

- First characterization of an FtsK-like protein in megalocytivirus (SKIV-FLP);
- SKIV-FLP locates below the major capsid protein (MCP) in purified virions;
- SKIV-FLP was confirmed containing three nuclear localization signals;
- SKIV-FLP was evidenced to act as a transcriptional inhibitor in vitro.

Prokaryotes contain many DNA binding proteins with large molecular weights and multiple domains. DNA binding proteins are involved in DNA replication, transcription, and other physiological processes. In this study, a DNA binding protein, containing an Ftsk-like protein (FLP) domain, was cloned and characterized from SKIV-ZJ07, a member of the RSIV-type megalocytivirus, using bioinformatics and molecular biology approaches. SKIV-FLP is 3762 base pairs long, encodes a viral protein of 1253 amino acid residuals, and contains an Ftsk (or EBV-NA3) and a Grx-2 domain. Virion localization indicated that SKIV-FLP is a major viral structural protein located below the major capsid protein. Laser confocal microscopy showed that SKIV-FLP is a cytoplasm-/nuclear-localized protein. However, the reconstruction experiments demonstrated that SKIV-FLP may contain three nuclear localization signals, each present in FLP-NT (1-380 aa), FtsK domain (380-880 aa), and Grx-2 domain (880-1253 aa). When SKIV-FLP was fused to the Gal-4 DNA-binding domain and co-transfected with L8G5-Luc, SKIV-FLP suppressed L8G5-Luc transcription. As a transcription inhibitor, SKIV-FLP also inhibited the transcription of NF-κB and IFN-γ (a type II IFN) promoter in HEK293T cells, suggesting that SKIV-FLP has a role in evading host immunity.