White spot syndrome virus protein ICP11: A histone-binding DNA mimic that disrupts nucleosome assembly

Abstract

White spot syndrome virus (WSSV) is a large (Ϸ300 kbp), doublestranded DNA eukaryotic virus that has caused serious disease in crustaceans worldwide. ICP11 is the most highly expressed WSSV nonstructural gene/protein, which strongly suggests its importance in WSSV infection; but until now, its function has remained obscure. We show here that ICP11 acts as a DNA mimic. In crystal, ICP11 formed a polymer of dimers with 2 rows of negatively charged spots that approximated the duplex arrangement of the phosphate groups in DNA. Functionally, ICP11 prevented DNA from binding to histone proteins H2A, H2B, H3, and H2A.x, and in hemocytes from WSSVinfected shrimp, ICP11 colocalized with histone H3 and activated-H2A.x. These observations together suggest that ICP11 might interfere with nucleosome assembly and prevent H2A.x from fulfilling its critical function of repairing DNA double strand breaks. Therefore, ICP11 possesses a functionality that is unique among the handful of presently known DNA mimic proteins.apoptosis ͉ DNase enhancer ͉ crystal structure ͉ shrimp aquaculture T he white spot syndrome virus (WSSV) is an enveloped DNA virus that infects crustaceans and threatens shrimp aquaculture (1-4). The white spot disease caused by WSSV can result in 100% cumulative mortality in farmed shrimps in 2-10 days. Based on studies of individual genes and analysis of the complete genome sequence, the ellipsoid-shaped WSSV has been erected as the type species of a new genus (Whispovirus) of a new virus family Nimaviridae (5). Because of the large size of the viral genome (Ϸ300 kb) and the uniqueness of the encoded proteins, WSSV has not yet been fully characterized.In previous studies, both transcriptomic (WSSV-infected EST database and WSSV DNA microarray) and proteomic (2D electrophoresis) approaches identified ICP11 as a highly expressed WSSV gene/protein (6, 7). The high expression levels of this protein strongly suggest its importance to WSSV infection; but until now, its function has remained unknown. In the present article, we determine the crystal structure of ICP11 and use Far Western assays and indirect immunofluorescence to investigate its function and the factors with which it interacts. We found that ICP11 acts as a DNA mimic that prevents DNA from binding to histone proteins and, thus, disrupts nucleosome assembly. Results ICP11 CrystalStructure. The protein model of ICP11 was built manually into a clear electron density map [supporting information (SI) Fig. S1 A] derived from MAD X-ray diffraction data. The refined structure contains 2 ICP11 molecules as a dimer per asymmetric unit (Fig. 1). The refinement statistics are listed in Table S1. Each monomer consists of a 4-stranded anti-parallel ␤-sheet, a 2-stranded ␤-ribbon, and 2 flanking ␣-helices ( Fig. 1 A and B). In the center of the monomer, 16-aa side chains are associated into a hydrophobic core. Every secondary structural element contributes to this core structure; thus, forming a stable compact globular fold. The nature of the dimer interface is largely...

Construction and Application of a Protein Interaction Map for White Spot Syndrome Virus (WSSV)

“…ICP11 (a DNA mimic protein) is the most highly expressed viral gene, making it a good indicator of WSSV infection (46,47). As shown in Fig.…”

Noncanonical DNA-binding mode of repressor and its disassembly by antirepressor

“…In this case, the Ant commonly mimics the structure of DNA to bind competitively to the Rep (5). DNA mimic proteins have been discovered in prokaryotes, eukaryotes, and viruses (5,6); these proteins are involved in various DNA regulatory functions, including transcriptional control (7) and DNA packaging (8). Although the structures of DNA-mimic proteins are diverse, they have similar surface-charge distributions that mimic the surface properties of DNA (5).…”

Viral ubiquitin ligase WSSV222 is required for efficient white spot syndrome virus replication in shrimp

“…It has been reported in several studies that significant WSSV gene expression can be detected in shrimp haemocytes by immunostaining (Wang et al, 2002(Wang et al, , 2008a or RT-PCR (Wang et al, 2008b). Shrimp haemocytes were shown to be the major target for WSSV attachment (Liang et al, 2005;Sritunyalucksana et al, 2006) and the main source of WSSV production (Syed Musthaq et al, 2006;Wang et al, 2002Wang et al, , 2008b.…”

“…In addition, shrimp haemocytes can easily be isolated from shrimp haemolymph as a pure, clean tissue sample without contamination from foreign proteins or tissues, compared with other shrimp tissues. Hence, shrimp haemocytes have been widely used in WSSV and shrimp studies to determine and quantify viral or cellular protein and gene expression accurately (Lin et al, 2002;Sritunyalucksana et al, 2006;Wang et al, 2008a). In this study, taking these advantages into consideration, haemocyte samples were exploited to study TSL protein expression and WSSV gene transcription.…”