CryoEM of Viral Ribonucleoproteins and Nucleocapsids of Single-Stranded RNA Viruses

Abstract

Single-stranded RNA viruses (ssRNAv) are characterized by their biological diversity and great adaptability to different hosts; traits which make them a major threat to human health due to their potential to cause zoonotic outbreaks. A detailed understanding of the mechanisms involved in viral proliferation is essential to address the challenges posed by these pathogens. Key to these processes are ribonucleoproteins (RNPs), the genome-containing RNA-protein complexes whose function is to carry out viral transcription and replication. Structural determination of RNPs can provide crucial information on the molecular mechanisms of these processes, paving the way for the development of new, more effective strategies to control and prevent the spread of ssRNAv diseases. In this scenario, cryogenic electron microscopy (cryoEM), relying on the technical and methodological revolution it has undergone in recent years, can provide invaluable help in elucidating how these macromolecular complexes are organized, packaged within the virion, or the functional implications of these structures. In this review, we summarize some of the most prominent achievements by cryoEM in the study of RNP and nucleocapsid structures in lipid-enveloped ssRNAv.

Cryo-EM structure of influenza helical nucleocapsid reveals NP-NP and NP-RNA interactions as a model for the genome encapsidation

“…In addition, our study sheds light on the divergence between nonsegmented and segmented negative-strand RNA viruses based on their nucleocapsid formation. For nonsegmented negative-strand RNA viruses, the Mononegavirales , like measles, rabies, and Ebola viruses for which the atomic structure of the NP bound to vRNA is known, the nucleocapsids are rather straight helices, and each protomer binds between 6 and 9 nt ( 29 ). However, the RNPs of the segmented viruses, like the Bunyavirales (the Bunyaviruses and the Arenaviruses), are very flexible, and the NP protomers bind between 7 and 11 nt ( 30 – 33 ), while the consensus for IAV, an Orthomyxoviridae , agrees on 20 to 26 nt per NP protomer ( 7 , 25 , 26 ).…”

Developments in Negative-Strand RNA Virus Reverse Genetics

“…During replication, the vRNA will synthesize full-length complementary RNA (cRNA). The cRNA can be utilized as a template for synthesizing a new negative-stranded RNA from the subsequent vRNA ( Figure 1 ) [ 10 , 11 , 12 , 13 , 14 ].…”

“…The cRNA can be utilized as a template for synthesizing a new negative-stranded RNA from the subsequent vRNA. (Figure 1) [10][11][12][13][14].…”

Advances in Structural Virology via Cryo-EM in 2022

“…As highlighted in the review conducted by Ramaswamy et al, cryo-EM has emerged as a powerful tool for unraveling the structural heterogeneity of RdRps at the atomic level, which results from the interaction of various factors such as nucleic acids, cofactors or inhibitors [ 12 ]. Similarly, there has been a considerable expansion in the number of nucleocapsid structures, which has helped to explain viral genome encapsidation, as elegantly summarized in [ 13 ]. Genome packaging is highly studied for bacteriophages and herpesviruses and plays a pivotal role in protecting, transporting and facilitating genetic exchange.…”