Biogénesis e inserción en membranas de proteínas de movimiento de virus vegetales

Abstract

The cell-to-cell movement of plant virus is assisted by the viral so-called movement proteins (MP). Functions assigned to these proteins include nucleic acid binding, targeting to the endoplasmic reticulum (ER), and modification of the size exclusion limit of the plasmodesmata, a membranous channel that connect adjacent cells. Although the number and size of these proteins vary from viral families it has been described that many of the viral MPs interact with the membranes but the nature of this interaction is not well defined yet. Therefore, the main goal of this study is the characterization of MPs interaction to the ER membranes. The Carnation Mottle Virus has been used as an experimental model. This virus encodes two MPs, a cytoplasmic soluble protein of 7 kDa, p7, which binds viral genome, and a hydrophobic protein of 9 kDa, p9, with two putative transmembrane segments. Firstly, it has been demonstrated that p9 is, in fact, an integral membrane protein containing two transmembrane segments and facing both N- and Cterminus to the cytosol. Secondly, it has been dissected the cellular pathway followed by p9 to reach the host membranes. This viral protein is targeted to ER membrane by the signal recognition particle, and the translocon components Sec61a and TRAM mediate p9 integration into the membrane. The unexpected results obtained in these studies are the following: (i) viral TM fragments integrate into the lipid bilayer through a sequentially ordered contact to Sec61a and TRAM; and (ii) TRAM mediates viral protein integration by collecting TM domains, which are only partitioned into the lipid bilayer after translation termination. Finally, it has been studied the topological determinants of p9 that govern the proper orientation of this viral membrane protein. It has been analysed contribution of different parameters such are distribution of positive residues along the protein sequence, hydrophobicity of transmembrane segments, length of extramembranous domains, and presence of aromatic residues flanking transmembrane domains. The results demonstrate that topological information of p9 is distributed along the amino acid sequence. This strategy could avoid any alteration of native topology of p9 due to a random mutation in the protein gene, a common process during viral genome replication.