Journal of Virology, September 2001, p. 8538-8546, Vol. 75, No. 18
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.18.8538-8546.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Station de Recherches de Pathologie Comparée, UMR 5087, INRA-CNRS-Université Montpellier II, 30380 Saint-Christol-les-Alès,1 Laboratoire de Spectrométrie de Masse Bio-Organique, 67087 Strasbourg Cedex 2,3 and Centre de Biochimie Structurale, INSERM U414, CNRS UMR 5048-Université Montpellier I Faculté de Pharmacie, 34060 Montpellier,4 France, and Friedrich Miescher Institut, CH-4002 Basel, Switzerland2
Received 26 March 2001/Accepted 5 June 2001
The helper component of Cauliflower mosaic virus is
encoded by viral gene II. This protein (P2) is dispensable for virus
replication but required for aphid transmission. The purification of P2
has never been reported, and hence its biochemical properties are largely unknown. We produced the P2 protein via a recombinant baculovirus with a His tag fused at the N terminus. The fusion protein
was purified by affinity chromatography in a soluble and biologically active form. Matrix-assisted laser desorption
time-of-flight mass spectrometry demonstrated that P2 is not
posttranslationally modified. UV circular dichroism revealed the
secondary structure of P2 to be 23%
-helical. Most
-helices are
suggested to be located in the C-terminal domain. Using size exclusion
chromatography and aphid transmission testing, we established that the
active form of P2 assembles as a huge soluble oligomer containing 200 to 300 subunits. We further showed that P2 can also polymerize as long
paracrystalline filaments. We mapped P2 domains involved in P2
self-interaction, presumably through coiled-coil structures, one of
which is proposed to form a parallel trimer. These regions have
previously been reported to also interact with viral P3, another
protein involved in aphid transmission. Possible interference between
the two types of interaction is discussed with regard to the biological
activity of P2.
Present address: Centre de Recherche en Infectiologie
PavillonCHUL, Université Laval, Ste-Foy, P.Q. G1V
4G2, Canada.
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