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. 2006 Dec;80(23):11678-85.
doi: 10.1128/JVI.00940-06. Epub 2006 Sep 13.

Mimivirus giant particles incorporate a large fraction of anonymous and unique gene products

Patricia Renesto  1 , Chantal Abergel, Philippe Decloquement, Danielle Moinier, Saïd Azza, Hiroyuki Ogata, Patrick Fourquet, Jean-Pierre Gorvel, Jean-Michel Claverie
Affiliations

Mimivirus giant particles incorporate a large fraction of anonymous and unique gene products

Patricia Renesto et al. J Virol. 2006 Dec.

Abstract

Acanthamoeba polyphaga mimivirus is the largest known virus in both particle size and genome complexity. Its 1.2-Mb genome encodes 911 proteins, among which only 298 have predicted functions. The composition of purified isolated virions was analyzed by using a combined electrophoresis/mass spectrometry approach allowing the identification of 114 proteins. Besides the expected major structural components, the viral particle packages 12 proteins unambiguously associated with transcriptional machinery, 3 proteins associated with DNA repair, and 2 topoisomerases. Other main functional categories represented in the virion include oxidative pathways and protein modification. More than half of the identified virion-associated proteins correspond to anonymous genes of unknown function, including 45 "ORFans." As demonstrated by both Western blotting and immunogold staining, some of these "ORFans," which lack any convincing similarity in the sequence databases, are endowed with antigenic properties. Thus, anonymous and unique genes constituting the majority of the mimivirus gene complement encode bona fide proteins that are likely to participate in well-integrated processes.

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Figures

FIG. 1.
FIG. 1.
Electron micrograph and SDS-PAGE of mimivirus. (A) Purified mimivirus particles (bar, 500 nm) separated by 11% SDS-PAGE and stained with Coomassie blue R250. (B) Bands in gels were excised for subsequent LC-MS/MS analysis after in-gel trypsin digestion. Identified proteins are listed in Table 1 (also see details in Table S1 in the supplemental material).
FIG. 2.
FIG. 2.
2D gel electrophoresis patterns of proteins. Acanthamoeba polyphaga mimivirus was separated using 18-cm pI 4 to 7 (left) or 6 to 11 (right) IPG strips for the first dimension (IEF) followed by 10% linear SDS-PAGE for the second dimension. Spots revealed by silver staining were cut out from the gel and subjected to trypsin digestion followed by MALDI-TOF-MS analysis. Molecular sizes and pI ranges are indicated. Identified proteins are listed in Table 1 (also see details in Table S1 in the supplemental material).
FIG. 3.
FIG. 3.
Glycosylation pattern of Acanthamoeba polyphaga mimivirus proteins detected by fluorescence assay. Mimivirus proteins were separated by 10% SDS-PAGE (A) or by 2D electrophoresis using 7-cm IPG strips (pI 3 to 10) (B), and glycosylated proteins were revealed with GlycoProfile III. Lane 1, standard glycosylation markers; lane 2, mimivirus.
FIG. 4.
FIG. 4.
Western blot analysis of mimivirus proteins. Mimivirus proteins were separated by 2D electrophoresis using 7-cm IPG strips (pI 3 to 10) and transferred to nitrocellulose membranes before incubation with serum from an immunized mouse as described in Materials and Methods.
FIG. 5.
FIG. 5.
Localization of Mimi_L725-encoded epitope. Ultrathin sections of mimivirus-infected amoebae were immunogold labeled with a monoclonal antibody raised against the MIMI_L725-encoded protein followed by goat anti-mouse antibodies conjugated to 25-nm colloidal gold particles before immunoelectron microscopy analysis. Bar, 200 nm.
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