Proteomic analysis of Chilo iridescent virus

Abstract

In this first proteomic analysis of an invertebrate iridovirus, 46 viral proteins were detected in the virions of Chilo iridescent virus (CIV) based on the detection of 2 or more distinct peptides; an additional 8 proteins were found based on a single peptide. Thirty-six of the 54 identified proteins have homologs in another invertebrate and/or in one or more vertebrate iridoviruses. The genes for 5 of the identified proteins, 22L (putative helicase), 118L, 142R (putative RNaseIII), 274L (major capsid protein) and 295L, are shared by all iridoviruses for which the complete nucleotide sequence is known and may therefore be considered as iridovirus core genes. Three identified proteins have homologs only in ascoviruses. The remaining 15 identified proteins are so far unique to CIV. In addition to broadening our insight in the structure and assembly of CIV virions, this knowledge is pivotal to unravel the initial steps in the infection process.

Fig. 1

SDS-PAGE profile and LC-MS/MS identification results of purified CIV virion proteins. CIV proteins were separated by 12% one-dimensional SDS-PAGE and stained with colloidal blue. The SDS-PAGE gel was divided into 6 slices, which, based on comparison to a molecular marker, ranged from higher than 95 kDa, 55–95 kDa, 43–55 kDa, 34–43 kDa, 26–34 kDa and lower than 26 kDa. Proteins were in-gel-digested with trypsin, extracted and subjected to LC-MS/MS. The column on the right indicates the relative abundance of the proteins as visualized by SDS-PAGE. The boxes on the left give the ORF numbers of the identified proteins in a particular gel slice in order of the predicted mass (see Table 1, Table 2). Underlined numbers represent single peptide hits. Indications R and L point towards the direction of transcription from the CIV genome (see Fig. 2).

Fig. 2

Linearized genomic presentation of the 54 CIV structural protein ORFs determined by LC-MS/MS. Arrows indicate the positions and the direction of gene transcription (R or L). Red arrows are ORFs unique to CIV, green arrows represent ORFs present in all sequenced iridovirus genomes. The yellow and the white ORFs, have an entomopox- and baculovirus homolog, respectively. The remaining ORFs are indicated in blue. Genomic positions are indicated on the right in base pair number.