Removal of divalent cations induces structural transitions in red clover necrotic mosaic virus, revealing a potential mechanism for RNA release.
The structure of Red clover necrotic mosaic virus (RCNMV), an icosahedral plant virus, was resolved to 8.5 A by cryoelectron microscopy. The virion capsid has prominent surface protrusions and subunits with a clearly defined shell and protruding domains. The structures of both the individual capsid protein (CP) subunits and the entire virion capsid are consistent with other species in the Tombusviridae family. Within the RCNMV capsid, there is a clearly defined inner cage formed by complexes of genomic RNA and the amino termini of CP subunits. An RCNMV virion has approximately 390 +/- 30 Ca2+ ions bound to the capsid and 420 +/- 25 Mg2+ ions thought to be in the interior of the capsid. Depletion of both Ca2+ and Mg2+ ions from RCNMV leads to significant structural changes, including (i) formation of 11- to 13-A-diameter channels that extend through the capsid and (ii) significant reorganization within the interior of the capsid. Genomic RNA within native capsids containing both Ca2+ and Mg2+ ions is extremely resistant to nucleases, but depletion of both of these cations results in nuclease sensitivity, as measured by a significant reduction in RCNMV infectivity. These results indicate that divalent cations play a central role in capsid dynamics and suggest a mechanism for the release of viral RNA in low-divalent-cation environments such as those found within the cytoplasm of a cell.
Sherman
Michael B
MB
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA. mbsherma@utmb.edu
Guenther
Richard H
RH
Tama
Florence
F
Sit
Tim L
TL
Brooks
Charles L
CL
Mikhailov
Albert M
AM
Orlova
Elena V
EV
Baker
Timothy S
TS
Lommel
Steven A
SA
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D002213:Capsid / Q000378:metabolism / Q000648:ultrastructure; D036022:Capsid Proteins / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D002413:Cations, Divalent / Q000378:metabolism; D020285:Cryoelectron Microscopy; D007091:Image Processing, Computer-Assisted; D008274:Magnesium / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D055672:Static Electricity; D019183:Tombusviridae / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure*
D036022:Capsid Proteins; D002413:Cations, Divalent; D046912:Multiprotein Complexes; D012367:RNA, Viral; D008274:Magnesium; D002118:Calcium