Scientists have recently discovered the structure of a key protein on the surface of the mimivirus that could potentially assist in research to identify its unknown functions and hosts.

Little is still known about mimivirus' natural hosts in the wild, and even though the mimivirus has been studied in a laboratory while infecting amoebas, many details cannot be verified, according to Michael G. Rossmann, a Hanley Distinguished Professor of Biological Sciences at Purdue University.

A team of scientists, led by Prof. Rossmann, discovered that the structure of an important enzyme-like protein known as R135, is comparable to aryl-alcohol oxidase, an enzyme found in fungus that is involved in biodegrading lignin in walls of a plant cell. The R135 is contained in fibers on the outer surface of the mimivirus.

In laboratory research where mimivirus is propagated inside a single-cell amoeba, the scientists introduced a satellite virus known as Sputnik that can only be grown in combination with another virus. The scientists then allowed both mimivirus and Sputnik to multiply inside the amoeba by duplicating their DNA. The protein R135's structure was then defined after using a scientific technique called X-ray crystallography. With this information of R135 acting similarly to aryl-alcohol oxidase, the scientists concluded that the protein R135, located in the mimivirus' fibers, participates during the infection of mimivirus to its hosts.

The mimivirus was originally believed to be a bacterium as its appearance is much bigger than most identified viruses. It was initially isolated by French scientists back in 1992 but was only established as a virus in 2003.

Mimiviruses are among the biggest identified viruses. The mimivirus is close to the size of a bacterium, and with a diameter of about half of a micron, it is more than 10 times bigger than the virus recognized as the source of common cold and could be large enough to be viewed with a light microscope. Most viruses are too tiny to be analyzed with traditional light microscopes.

It was also discovered that oysters are rich with mimiviruses and that these sea creatures could be utilized as alternative hosts in future studies of structuring mimivirus. Scientists also discovered that humans have natural antibodies against mimivirus and that they are located inside specialized cells in humans known as macrophages. It is not yet established if mimivirus could infect humans.

The study has earned financial grants from the National Institutes of Health.

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