Structure of Surface Protein of Very Large Mimiviruses Identified, May Provide New Clues to This Highly Mysterious Virus

Researchers have discovered the structure of a key protein on the surface of an unusually large virus called the mimivirus, aiding efforts to determine its hosts and unknown functions. The mimivirus was initially thought to be a bacterium because it is much larger than most viruses. It was isolated by French scientists in 1992, but was not confirmed to be a virus until 2003. In the laboratory, the virus has been studied while infecting amoebas, but its natural hosts in the wild and many other details about the virus remain unknown, said Dr. Michael Rossmann, Purdue University's Hanley Distinguished Professor of Biological Sciences. He led a team of researchers who discovered the structure of a key, enzyme-like protein called R135, which is contained in fibers on the outer surface of the virus. The structure of R135 is similar to an enzyme called aryl alcohol oxidase, which is found in a fungus and is involved in biodegrading lignin in plant cell walls. "This could tell us something about the mimivirus's natural hosts," Dr. Rossmann said. "We think there must be another host, something different than amoebas, and that this enzyme helps the virus get into this host. Perhaps R135 participates in the degradation of lignin so that the virus can enter a host such as lignin-containing algae." Also suggesting the possibility of alternative hosts is the recent discovery that mimivirus has been found to be abundant in oysters. Antibodies against mimivirus have been found in humans, and the virus has been discovered inside specialized cells in humans called macrophages, but whether it actually infects people is not known. "I wouldn't say it infects humans, but it can propagate in humans because macrophages take up this virus and it can propagate in these," said Dr.
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