Atomic force microscopy investigation of the giant mimivirus

Yuri G Kuznetsov,Chuan Xiao,Siyang Sun,Didier Raoult,Michael Rossmann,Alexander Mcpherson

doi:10.1016/j.virol.2010.05.007

Abstract

Mimivirus was investigated by atomic force microscopy in its native state following serial degradation by lysozyme and bromelain. The 750-nm diameter virus is coated with a forest of glycosylated protein fibers of lengths about 140 nm with diameters 1.4 nm. Fibers are capped with distinctive ellipsoidal protein heads of estimated Mr = 25 kDa. The surface fibers are attached to the particle through a layer of protein covering the capsid, which is in turn composed of the major capsid protein (MCP). The latter is organized as an open network of hexagonal rings with central depressions separated by 14 nm. The virion exhibits an elaborate apparatus at a unique vertex, visible as a star shaped depression on native particles, but on defibered virions as five arms of 50 nm width and 250 nm length rising above the capsid by 20 nm. The apparatus is integrated into the capsid and not applied atop the icosahedral lattice. Prior to DNA release, the arms of the star disengage from the virion and it opens by folding back five adjacent triangular faces. A membrane sac containing the DNA emerges from the capsid in preparation for fusion with a membrane of the host cell. Also observed from disrupted virions were masses of distinctive fibers of diameter about 1 nm, and having a 7-nm periodicity. These are probably contained within the capsid along with the DNA bearing sac. The fibers were occasionally observed associated with toroidal protein clusters interpreted as processive enzymes modifying the fibers.

Highlights

Mimivirus (Acanthamoeba polyphaga mimivirus) warrants special attention owing to its size, complexity, and its evolutionary ambiguity
There is some evidence that mimivirus can be associated with human pneumonia (Raoult et al, 2004; 2007), it is the focus of particular interest because its genomic, metabolic, and structural
The strategy we pursued in dissecting mimivirus, seen attached to host cell membrane in Figs. 1a and b, was essentially the same as was employed in the dissection of vaccinia virus (Kuznetsov et al, 2008), a combination of chemical, enzymatic, and physical procedures designed to strip away successive layers of structure to reveal the one below

Summary

Introduction

Mimivirus (Acanthamoeba polyphaga mimivirus) warrants special attention owing to its size, complexity, and its evolutionary ambiguity. It is the largest virus known, having a diameter of 700 to 750 nm based on electron microscopy (Xiao et al, 2005; 2009; Zauberman et al, 2008) and a genome size of 1.2 million base pairs (Raoult et al, 2004), nearly twice that of any other known virus. There is some evidence that mimivirus can be associated with human pneumonia (Raoult et al, 2004; 2007), it is the focus of particular interest because its genomic, metabolic, and structural.

Methods

Results

Conclusion