Crystal Structures of Major Envelope Proteins VP26 and VP28 from White Spot Syndrome Virus Shed Light on Their Evolutionary Relationship

Abstract

White spot syndrome virus (WSSV) is a virulent pathogen known to infect various crustaceans. It has bacilliform morphology with a tail-like appendage at one end. The envelope consists of four major proteins. Envelope structural proteins play a crucial role in viral infection and are believed to be the first molecules to interact with the host. Here, we report the localization and crystal structure of major envelope proteins VP26 and VP28 from WSSV at resolutions of 2.2 and 2.0 Å, respectively. These two proteins alone account for approximately 60% of the envelope, and their structures represent the first two structural envelope proteins of WSSV. Structural comparisons among VP26, VP28, and other viral proteins reveal an evolutionary relationship between WSSV envelope proteins and structural proteins from other viruses. Both proteins adopt ␤-barrel architecture with a protruding N-terminal region. We have investigated the localization of VP26 and VP28 using immunoelectron microscopy. This study suggests that VP26 and VP28 are located on the outer surface of the virus and are observed as a surface protrusion in the WSSV envelope, and this is the first convincing observation for VP26. Based on our studies combined with the literature, we speculate that the predicted N-terminal transmembrane region of VP26 and VP28 may anchor on the viral envelope membrane, making the core ␤-barrel protrude outside the envelope, possibly to interact with the host receptor or to fuse with the host cell membrane for effective transfer of the viral infection. Furthermore, it is tempting to extend this host interaction mode to other structural viral proteins of similar structures. Our finding has the potential to extend further toward drug and vaccine development against WSSV.In the shrimp aquaculture industry, more than 20 viruses have been reported to date. Of these, white spot syndrome virus (WSSV) is the major and most serious pathogen (4,5,24). The virulence of WSSV is very high, resulting in mortality rates from 90 to 100% within 3 to 7 days of infection and leading to complete devastation of the shrimp culture industry. This virus has a wide range of hosts among crustaceans and induces distinctive clinical signs of white spots on the carapace, appendages, and the inner surface of the body. WSSV belongs to a new virus family, Nimaviridae, under a new genus Whispovirus (www.ncbi.nih.gov/ICTVdb/Ictv/index.htm), which shares a low homology with other known DNA viruses (25, 41). WSSV is an enveloped virus with a 305-kb double-stranded circular DNA genome (41,46) and approximately 180 open reading frames. However, most of its presumptive open reading frames do not have any homology with known proteins and are functionally unknown.In order to understand the mechanism of WSSV infection and morphogenesis, we focused on the characterization of structural proteins. Among these structural proteins, the envelope proteins are extremely important because they are believed to be the first molecules to interact with the host and, consequently, pl...

Generation of recombinant monoclonal antibodies to study structure–function of envelope protein VP28 of white spot syndrome virus from shrimp

“…The underline indicates the restriction enzyme site. a-helix and b-strand are indicated as a1, a2, b1, b2, b8, and b9 according to Tang et al [11].…”

“…According to the crystal structure of VP28 resolved by Tang et al [11] and the predicted trimer structural model, the epitopes in the region of VP28 between amino acid 28-67 have possibility in the inner of the trimer, so scFv P108D2 and P111B10 can not bind to the epitopes when VP28 is in tightly packed envelope. They may expose to the surface out of the trimer and recognized by antibodies when VP28 is in loosely packed envelope.…”

“…The crystal structure of VP28 was first reported in 2007. It adopts a single b-barrel architecture with a protruding N-terminal a-helix and might anchor as trimer on the envelope membrane surface through the N-terminal transmembrane region [11]. Neutralization experiments with the polyclonal serum against VP28 in vivo have suggested that VP28 may be involved in the WSSV systemic infection of shrimp [12].…”

Molecular cloning and recombinant expression of the VP28 carboxyl-terminal hydrophilic region from a brazilian white spot syndrome virus isolate

“…This virus contains five major structural proteins, located in the viral envelope (VP19 and VP28) and in the nucleocapsid (VP15, VP24 and VP26). VP28 (~22 kDa) is the most abundant structural protein present in the envelope (Tang et al, 2007) and shows no similarity with other known proteins, except with some structural proteins of WSSV (Robalino et al, 2006). This envelope protein was suggested to bind to shrimp cells, playing a crucial role in the viral penetration (Yi et al, 2004).…”

“…Since currently there is no effective treatment for shrimp viral diseases, and vaccines cannot be developed and used in shrimp aquaculture due to the lack of adaptive immune system in crustaceans (Liu et al, 2009), rapid diagnosis is one of the most valid strategies to curtail the WSSV infection. Moreover, structural recombinant WSSV proteins can be used in order to understand the mechanisms of WSSV infection, morphogenesis and interaction with host molecules (Tang et al, 2007). WSSV has been isolated from different geographic regions, such as Korea, Thailand, China and Americas (Lightner, 2003).…”