The mysterious Mimivirus
Researchers using the GM/CA-XSD 23-ID-B and 23-ID-D beamlines at the APS have discovered a key protein structure on the surface of the Mimivirus. The discovery will aid efforts to determine mimivirus functions.
Mimivirus is one of the largest viruses discovered to date and little is known about how it infects its host. Determining the structure of R135, a protein that assists Mimivirus in entering its natural host, can provide new information about both the virus and its hosts.
Mimivirus was initially identified as a bacterium because its dense, 125-nm-long fibers stained Gram-positively. These fibers probably play a role during the infection of some host cells. The normal hosts of Mimivirus are unknown, but in the laboratory Mimivirus is usually propagated in amoeba. The structure of R135, a major component of the fibrous outer layer of Mimivirus, has been determined to 2-Å resolution. The protein’s structure is similar to that of members of the glucose-methanol-choline oxidoreductase family, which have an N-terminal FAD binding domain and a C-terminal substrate recognition domain. The closest homolog to R135 is an aryl-alcohol oxidase that participates in lignin biodegradation of plant cell walls. Thus R135 might participate in the degradation of their normal hosts, including some lignin-containing algae.
Thomas Klose, Dominik A. Herbst, Hanyu Zhu, Joann P. Max, Hilkka I. Kenttsamaa and Michael G. Rossmann, “A Mimivirus Enzyme that Participates in Viral Entry,” Structure 23, DOI:10.1016/j.str.2015.03.023, Published Online May 14, 2015.