Helical capsids of plant viruses: architecture with structural lability

Abstract

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.

Non-replicative Integral Membrane Proteins Encoded by Plant Alpha-Like Viruses: Emergence of Diverse Orphan ORFs and Movement Protein Genes

“…These findings indicated that movement gene modules composed of two or more cistrons may encode at least one nucleic acid-binding protein and at least one trans-membrane movement protein, which can be rather small. Further studies revealed that, in some cases, multi-component transport modules do not encode dedicated nucleic acid-binding MP, and this function can be performed by viral capsid proteins, as in RNA-containing viruses of the families Closteroviridae and Potyviridae, which employ their flexuous filamentous virions as a transport form of viral genome ( Rodríguez-Cerezo et al, 1997 ; Roberts et al, 1998 ; Dolja et al, 2006 ; Solovyev and Makarov, 2016 ) and DNA-containing viruses of genus Mastrevirus (family Geminiviridae) and the family Nanoviridae ( Mandal, 2010 ; Fondong, 2013 ). On the other hand, membrane proteins are always found among MPs of multicomponent viral transport systems.…”

Small hydrophobic viral proteins involved in intercellular movement of diverse plant virus genomes

“…Moreover, this domain is conserved in almost all capsid proteins of filamentous viruses, thus suggesting that p60 may directly interact with RNA [101] – [103] , [110] , [111] . It has been proposed that the tail of closteroviral virions evolved to facilitate cell-to-cell and systemic transport of the large closterovirus encapsidated genomic RNAs [111] , [112] . Indeed, virions and Hsp70h were found in PD [112] , [113] .…”

Ins and Outs of Multipartite Positive-Strand RNA Plant Viruses: Packaging versus Systemic Spread

“…The reconstruction of TMV from purified CP and viral RNA [21] set up the fundamental basis for understanding rod-shaped and flexuous helicoidal viruses that has been recently reviewed elsewhere [5]. Upon the recognition of an RNA signature on the viral genome, CP nucleates and cooperatively recruits further copies of structural proteins to cover the entire genome with a first coverage of the 5′ domain followed by the protection of the 3′ terminus.…”

“…A.L.N. Rao has reviewed mechanisms driving genome packaging of spherical plant RNA viruses [4] while Solovyev and Makarov recently focused on plant viruses with helical capsids [5]. …”