Comparative cryo-EM structures of CGMMV and ToMMV reveal divergent coat protein packing and electrostatics indicating Tobamovirus host specificity

Abstract

Tobamoviruses are a group of economically important plant viruses exhibiting extreme stability and persistence. Despite high morphological similarity, they show extensive host-family specificity, induce a wide range of symptoms, and inflict significant global yield losses in fruit and vegetable crops. Composed of a rod-shaped helical assembly of identical coat proteins encasing a single-stranded RNA, tobamoviruses have long served as fundamental models for understanding helical assemblies. Here we report the cryo-EM structures of two viruses from this genus, cucumber green mottle mosaic virus (CGMMV) and tomato mottle mosaic virus (ToMMV), at 2.86 [A] and 2.71 [A] resolution, respectively, revealing divergent packing strategies within the virion assembly. Whereas the solanaceous-infecting ToMMV closely mirrors genetically-similar canonical tobacco mosaic virus (TMV), CGMMV employs a specialized hydrophobic packing strategy based at the solvent-exposed inner loop lining the solvent-exposed central canal. Comparative biophysical and molecular dynamics analyses from the reconstructed structures reveal more stable and compact protein packing for CGMMV at both the subunit and assembly levels. Furthermore, we identify a conserved electrostatic pentapeptide motif (residues 113 to117) on the lower radial alpha helix that serves as an additional RNA-stabilizing region, harbouring a clade-defining Lys113 synapomorphy in cucurbit-infecting tobamoviruses. Together, our findings elucidate how subtle electrostatic tuning and divergent hydrophobic packing strategies drive differential virion stability and host-family adaptation within a strictly conserved helical scaffold.

Abstract as supplied by the indexing source. © the authors / publisher.