High resolution analysis of the readthrough domain of beet necrotic yellow vein virus readthrough protein: a KTER motif is important for efficient transmission of the virus by Polymyxa betae

Three 'triple gene block' proteins known as TGBp1, TGBp2 and TGBp3 are required for cell-tocell movement of plant viruses belonging to a number of genera including Hordeivirus. Hordeiviral TGBp1 interacts with viral genomic RNAs to form ribonucleoprotein (RNP) complexes competent for translocation between cells through plasmodesmata and over long distances via the phloem. Binding of hordeivirus TGBp1 to RNA involves two protein regions, the C-terminal NTPase/ helicase domain and the N-terminal extension region. This study demonstrated that the extension region of hordeivirus TGBp1 consists of two structurally and functionally distinct domains called the N-terminal domain (NTD) and the internal domain (ID). In agreement with secondary structure predictions, analysis of circular dichroism spectra of the isolated NTD and ID demonstrated that the NTD represents a natively unfolded protein domain, whereas the ID has a pronounced secondary structure. Both the NTD and ID were able to bind ssRNA non-specifically. However, whilst the NTD interacted with ssRNA non-cooperatively, the ID bound ssRNA in a cooperative manner. Additionally, both domains bound dsRNA. The NTD and ID formed low-molecular-mass oligomers, whereas the ID also gave rise to high-molecular-mass complexes. The isolated ID was able to interact with both the NTD and the C-terminal NTPase/helicase domain in solution. These data demonstrate that the hordeivirus TGBp1 has three RNA-binding domains and that interaction between these structural units can provide a basis for remodelling of viral RNP complexes at different steps of cell-to-cell and long-distance transport of virus infection. INTRODUCTIONTransport of plant viruses from cell to cell occurs through plasmodesmata and requires virus-encoded movement proteins (Boevink & Oparka, 2005;Lucas, 2006;Epel, 2009). In the genus Hordeivirus, viral movement proteins are represented by three proteins encoded by a 'triple gene block' (TGB) and referred to as TGBp1, TGBp2 and TGBp3 (Solovyev et al., 1996). The TGB is a conserved module of overlapping genes found in a number of virus groups (Morozov & Solovyev, 2003). Hordeivirus TGBp1 binds viral genomic RNA forming a cell-to-cell transportcompetent complex (Brakke et al., 1988;Kalinina et al., 2001;Lim et al., 2008;Jackson et al., 2009). TGBp2 and TGBp3 are small membrane proteins necessary for intracellular transport of complexes containing TGBp1 and viral RNA to plasmodesmata (Morozov & Solovyev, 2003;Zamyatnin et al., 2004; Haupt et al., 2005;Jackson et al., 2009 Lim et al., 2008;Jackson et al., 2009). Such TGBp1-RNA complexes are considered to be a form of viral genome capable of cell-to-cell and long-distance transport in plants (Morozov & Solovyev, 2003;Lim et al., 2008). In potex-like TGBs, the whole TGBp1 sequence is represented by the NTPase/helicase domain (HELD) with seven conserved motifs of the superfamily 1 NTPases/helicases (Gorbalenya et al., 1989), whereas the hordei-like TGBp1 has an additional N-terminal 'extension region' (Morozov & Solovyev, ...

Section: Discussionmentioning

confidence: 99%

Domain organization of the N-terminal portion of hordeivirus movement protein TGBp1

Makarov

Rybakova

Ефимов

et al. 2009

“…As suggested for some benyviruses, furoviruses and pomoviruses (Adams et al, 2001), the electrostatic interaction between these basic (K) and acidic (D) residues at the inner side of the membrane is necessary for an efficient viral transmission by the protist vector. In that way, the D residue corresponds to the E residue from the KTER motif, described as essential for the transmission of BNYVV by Polymyxa betae (Tamada et al, 1996). It is also worth noting that no amino acid changes were observed for these two motifs among all ten sequenced BVQ strains originating from six countries.…”

Section: Journal Of General Virology 90mentioning

confidence: 99%

“…This hypothesis is now confirmed with the identification of the common longer putative 76 kDa RT domain. Spontaneous deletions in the coat protein RT domain have been reported for other furoviruses sensu lato (Tamada & Kusume, 1991;Chen et al, 1994;Tamada et al, 1996;Reavy et al, 1998) that, when mechanically inoculated in a repeated way, show some deletion events in the C-terminal part of the RT domain. Therefore, as the BVQ strain described in 1998 had been submitted to multiple mechanic inoculation cycles on Chenopodium quinoa, it can be assumed that three deletion events of 5, 285 and 1 nt occurred in genomic RNA-2.…”

Section: Journal Of General Virology 90mentioning

confidence: 99%

The beet virus Q coat protein readthrough domain is longer than previously reported, with two transmembrane domains

Crutzen

Kreit

Bragard

2009

Ten beet virus Q (BVQ) strains from six different countries were sequenced to characterize the readthrough (RT) domain of the coat protein (CP). The GenBank/EMBL/DDBJ accession numbers for the sequences reported in this paper are FM244643-FM244652. With three nucleotide additions of 5, 285 and 1 nt, the common RT of 76 kDa was found to be longer than the single reference available to date (35 kDa). It is hypothesized that multiple inoculation cycles on Chenopodium quinoa were responsible for these three deletions in the C-terminal part of the BVQ RNA-2 previously described. Two putative transmembrane domains, TM1 and TM2, were predicted in the consensus amino acid sequence of the ten BVQ strains, and the putative BVQ TM2 was aligned with that of potato mop-top virus.

“…In contrast to filamentous viruses translocated through plasmodesmata as virions or virion-like structures, the CP of rodshaped viruses is not required for viral cell-to-cell movement (Herzog et al, 1998;Petty & Jackson, 1990;Saito et al, 1990;Savenkov et al, 2003;Schmitt et al, 1992;Tamada et al, 1996;Ziegler-Graff et al, 1991). In these viruses, the transport form of the virus genome is assumed to be a non-virion RNP, as has been reported for well-studied TMV and BSMV (Brakke et al, 1988;Citovsky et al, 1990Citovsky et al, , 1992.…”

Section: Role Of Virions In Cell-to-cell Transport Of Filamentous Virmentioning

confidence: 98%

Helical capsids of plant viruses: architecture with structural lability

Solovyev

Makarov

2016

Capsids of numerous filamentous and rod-shaped plant viruses possess helical symmetry. In positive-stranded RNA viruses, helical capsids are typically composed of many identical subunits of the viral capsid protein (CP), encapsidating a molecule of viral genomic RNA. Current progress in structural studies of helical plant viruses has revealed differences between filamentous and rod-shaped viruses, both in structural folds of their CPs and in the interactions of CP molecules in their capsids. Many filamentous and rod-shaped viruses have functionally similar lateral inter-subunit contacts on the outer virion surface. Additionally, the extreme Nterminal CP region in filamentous viruses is intrinsically disordered. Taken together, the available data establish a link between the structural features of molecular interactions of CP molecules and the physical properties of helical virions ranging from rigidity to flexibility. Overall, the structure of helical plant viruses is significantly more labile than previously thought, often allowing structural transitions, remodelling and the existence of alternative structural forms of virions. These properties of virions are believed to be functionally significant at certain stages of the viral life cycle, such as during translational activation and cell-to-cell transport. In this review, we discuss structural and functional features of filamentous and rod-shaped virions, highlight their shared features and differences, and lay emphasis on the relationships between the molecular structure of viral capsids and their properties including virion shape, lability and capability of structural remodelling.