A Mimivirus Enzyme that Participates in Viral Entry

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.