ИСТИНА

BACKGROUND: Alternanthera mosaic virus (AltMV) is a filamentous plant virus belonging to the genus Potexvirus. The virus contains a single-strand RNA and coat protein, that self-assembles around RNA into a flexible helical sheath. In contrast to rich information on the rigid rod plant viruses, structural information for flexible plant viruses has been lacking. The only high-resolution structure of a part of CP is available for PapMV, and for some other Potexviruses only low-resolution structures exist. OBSERVATIONS: The aim of this work is to determine the structure of AltMV using cryo-EM and image processing. The virus particles were purified as described in Mukhamedzhanova et al. (2009) and quickly frozen in liquid ethane. The high resolution data were collected on Titan Krios electron microscope (FEI) at 300 kV acceleration voltage using Falcon direct detector. Image processing has been accomplished using software packages IMAGIC and Spider. All images (1200 single particles) were corrected for the CTF. Collected data show that viral particle has a diameter of 135Å. The helical parameters were estimated. The obtained 3D map of electron density has a resolution of 8Å. It shows that there is a central channel inside the particle with ~18Å in diameter. There is a electron density at 36Å radius that is probably a viral RNA. The obtained resolution allows to trace alpha-helices and make a fitting of a homology model of the coat protein. The high radius region of AltMV is similar to that of PapMV and this can be explained by high homology of CPs of these viruses. The fitting reveals the inter-subunit contact by means of N-terminal loop from one subunit and hydrophobic pocket from neighbor subunit. CONCLUSIONS: The overall structure of AltMV CP subunit is different from that in rigid rod shaped plant viruses and similar to PapMV CP structure. The hydrophobic contact between N-terminal loop and neighbor subunit earlier observed in PapMV may explain the flexibility of AltMV virions.