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J Mol Biol. 2005 Feb 11;346(1):267-77. Epub 2004 Dec 18.

Structure of the mature P3-virus particle complex of cauliflower mosaic virus revealed by cryo-electron microscopy.

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Université Rennes I, UMR 6026 CNRS, Campus de Beaulieu, 35042 Rennes, France.


The cauliflower mosaic virus (CaMV) has an icosahedral capsid composed of the viral protein P4. The viral product P3 is a multifunctional protein closely associated with the virus particle within host cells. The best-characterized function of P3 is its implication in CaMV plant-to-plant transmission by aphid vectors, involving a P3-virion complex. In this transmission process, the viral protein P2 attaches to virion-bound P3, and creates a molecular bridge between the virus and a putative receptor in the aphid's stylets. Recently, the virion-bound P3 has been suggested to participate in cell-to-cell or long-distance movement of CaMV within the host plant. Thus, as new data accumulate, the importance of the P3-virion complex during the virus life-cycle is becoming more and more evident. To provide a first insight into the knowledge of the transmission process of the virus, we determined the 3D structures of native and P3-decorated virions by cryo-electron microscopy and computer image processing. By difference mapping and biochemical analysis, we show that P3 forms a network around the capsomers and we propose a structural model for the binding of P3 to CaMV capsid in which its C terminus is anchored deeply in the inner shell of the virion, while the N-terminal extremity is facing out of the CaMV capsid, forming dimers by coiled-coil interactions. Our results combined with existing data reinforce the hypothesis that this coiled-coil N-terminal region of P3 could coordinate several functions during the virus life-cycle, such as cell-to-cell movement and aphid-transmission.

[Indexed for MEDLINE]

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