JVI Accepts, published online ahead of print on 4 November 2009

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J. Virol. doi:10.1128/JVI.01957-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Structural Studies of the Sputnik Virophage

Siyang Sun, Bernard La Scola, Valorie D. Bowman, Christopher M. Ryan, Julian P. Whitelegge, Didier Raoult, and Michael G. Rossmann^*

Department of Biological Sciences, 915 W. State Street, Purdue University, West Lafayette, IN 47907-2054, USA; URMITE, Centre National de la Recherche Scientifique UMR IRD 6236, Faculté de Médecine, Université de la Méditerranée, 27 Boulevard Jean Moulin, 13385 Marseille Cedex 5, France; The Pasarow Mass Spectrometry Laboratory, The NPI-Semel Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90024-1759, USA

^* To whom correspondence should be addressed. Email: mr{at}purdue.edu.

The virophage Sputnik is a satellite virus of the giant Mimivirus and is the only satellite virus reported to date whose propagation adversely affects its host virus' production. Genome sequence analysis showed that Sputnik has genes related to viruses infecting all three domains of life. Here, we report structural studies of Sputnik which show that it is about 740 Å in diameter, has a T=27 icosahedral capsid, and has a lipid membrane inside the protein shell. Structural analyses suggest that the major capsid protein of Sputnik is likely to have a double jelly-roll fold, although sequence alignments do not show any detectable similarity with other viral double jelly-roll capsid proteins. Hence, the origin of Sputnik's capsid might have been derived from other viruses prior to its association with Mimivirus.