Mimivirus
Mimivirus, which is the only member of the newly suggested Mimiviridae family, is the largest known icosahedral virus. Both the physical dimension and genome size of Mimivirus are comparable to small bacteria. The virion of Mimivirus, which contains a dsDNA genome of 1.2 mega base pair, has a diameter of 5,000 Å, covered by 1,200 Å long fibers, and appears to have at least two lipid membranes within its protein capsid. A unique vertex, presumably for attachment and infection of the host, can be seen for particles that have a suitable orientation on the micrographs.
Currently we are using cryo-EM and cryo-tomography to study the structure of the Mimivirus.
Whereas the famous Farnese Atlas statue at the National Archaeological Museum in Naples shows Atlas supporting the Earth´s globe on his shoulders, here Atlas is holding the largest known virus. Maybe Atlas, representing mankind, is winning out over the weight of the viral pathogens.
CryoEM images of Mimivirus. CryoEM images were collected on an FEI CM300 microscope with a field emission gun operated at an accelerating voltage of 300 kV, a liquid nitrogen stage, and a defocus range of 13µm to 20µm.
(A) An array of particles separated by the viral fibers. (B) An enlarged view of one particle showing at least two possible lipid layers (straight arrows), the unanchored nuclear capsid (white arrow head), the protein capsid (between jagged arrows), and the fibers with their 200 Å thick base layer (black arrow head) . (C) Enlarged view of one particle showing a unique vertex (black arrow) whose width is about 600 Å. Radial distances from the center of the virus are shown in Å. The scale bars represent 2,000 Å.
CryoEM 3D reconstructions.
(A) shows surface shaded 3D image reconstructions whereas (B) shows a central cross-section slab about 50 Å thick. The left half of (A) and (B) are at a contour level that includes the denser base layer of the fibers whereas the right half of (A) and (B) are at a higher contour level that shows the capsid. The internal unanchor-ed nucleocapsid can be seen in the left side of (B) between 800 Å to 1,500 Å radii. Radial distances from the center are shown in Å on panel B and can be compared to those on panel B in the top figure. The scale bar represents 2,000 Å.
Collaborators : Didier Raoult of Faculté de Médecine of Marseille, France.