Biology subjects

Sherlock, M. E.

Publications and source records attributed to Sherlock, M. E..

7 recordsLinked to original sources

bioRxiv2026

An A-rich linker between dengue virus tandem xrRNAs facilitates functional coordination

Orthoflaviviruses use programmed resistance to host 5' to 3' exoribonucleases to produce subgenomic flaviviral RNAs (sfRNAs) during infection. This resistance is conferred by exoribonuclease-resistant RNA (xrRNA) structures that often occur in tandem and whose function can be coupled. In dengue virus serotype 2 (DENV2) this coupling results in changing patterns of sfRNA identity and abundance linked to the ability of the virus to adapt to host vs. vector infections. The physical basis of this coupling was unknown. Using a combination of virology, biochemistry, bioinformatics, structural biology, and biophysics, we explored the structural and sequence determinants of tandem xrRNA coupling in DENV2. We discovered that the spatial proximity, order, and structural integrity of the tandem xrRNAs are all important for coupling. Furthermore, an unpaired A-rich linker that lies between the two xrRNAs is essential in stabilizing a specific structure that correlates to coupling. This A-rich sequence likely forms tertiary contacts with an adjacent stem-loop structure to form a physical bridge between the two xrRNAs, a finding that is supported by a mid-resolution cryoEM map of the DENV2 tandem xrRNAs. Disruption of the structure of this bridge by mutation changes the relative orientation or spacing between the tandem xrRNAs, which is correlated to their functional coupling. These findings provide an explanation for the coupling between tandem xrRNAs and suggests new mechanistic hypotheses. IMPORTANCEDengue virus (DENV) generates non-coding subgenomic flaviviral RNAs (sfRNAs) that affect several cellular pathways and are important for successful infection. These sfRNAs are formed by structured RNA elements in the viral genome called exoribonuclease-resistant RNAs (xrRNAs), which fold into a distinct three-dimensional topology to block degradation by host cell exoribonucleases and often occur in tandem. Specific patterns of sfRNAs made during infection are important for host vs. vector fitness, and in DENV2 this pattern depends on functional coupling between tandem xrRNAs. However, the source of this functional coupling was unknown. We determined that an unpaired A-rich linker between the tandem xrRNAs is necessary for creating a structural bridge between the tandem xrRNAs. This bridge appears to favor a specific orientation between the tandem xrRNAs that is correlated to coupling and therefore to the patterns and relative abundance of sfRNAs produced during infection.

microbiology↗

bioRxiv2025

A compact viral IRES translates a downstream open reading frame

Hepatitis C virus (HCV) and many other RNA viruses contain a Type IV internal ribosome entry site (IRES) in their 5' untranslated region (UTR). These IRES RNAs adopt a complex tertiary structure that interacts directly with the ribosome, enabling cap-independent translation initiation. Using bioinformatic methods to search viral genomes for more Type IV IRES RNAs, we discovered that megrivirus E (MeV-E) contains a putative Type IV IRES within its annotated 3' UTR. In addition to its unusual location downstream of the main coding region, the size of the MeV-E 3' IRES is substantially reduced compared to known Type IV IRESs. We confirmed the secondary structure of the MeV-E 3' IRES, determined its 3D structure in complex with the ribosome using cryoEM, and showed that the MeV-E 3' IRES initiates translation but at lower levels compared to the larger Type IV IRES in the MeV-E 5' UTR. We hypothesize that the absence of several domains in the MeV-E 3' IRES compared to other Type IV IRESs results in a loss of ribosomal protein interactions and a relative decrease in translation activity. This small Type IV IRES enables translation of a second open reading frame in the MeV-E genome, which likely encodes a transmembrane protein that is conserved in other megriviruses. We propose a model wherein MeV-E expresses lower levels of its downstream-encoded protein compared to those in the upstream coding region using a pared down IRES structure, demonstrating purposeful tuning of translation through RNA structural variation.

microbiology↗

bioRxiv2025

Distribution and structural diversity of Type IV internal ribosome entry sites

Internal Ribosome Entry Sites (IRESs) are RNAs that facilitate cap- and end-independent translation initiation in eukaryotes. Type IV IRESs, which include the hepatitis C virus IRES, directly bind the 40S subunit and require only a subset of the canonical initiation factors to function. As the full diversity and species distribution of these IRESs was unknown, we sought to identify and classify their full architectural variation. Using a secondary structure homology-based search method, we identified 163 putative Type IV IRESs from viruses with diverse hosts and phylogeny, including the first example in a double stranded viral genome. Clustering analysis based on the presence and overall size of secondary structure elements yielded three distinct groups, differentiated by secondary structure expansions and deletions. Chemical probing of representative IRESs from each cluster validated the predicted secondary structures and in vitro translation assays showed that structural differences correlate with functional variation. Our findings reveal distinct structural adaptations and patterns within the Type IV IRESs that may influence IRES function and mechanism.

microbiology↗

bioRxiv2024

Tick-borne flavivirus exoribonuclease-resistant RNAs contain a 'double loop' structure

Flaviviridae viruses are human pathogens that generate subgenomic noncoding RNAs during infection using structured exoribonuclease resistant RNAs (xrRNAs) that block progression of host cells exoribonucleases. The structures of several xrRNAs from mosquito-borne and insect-specific flaviviruses have been solved, revealing a conserved fold in which a ring-like motif encircles the end of the xrRNA. However, the xrRNAs found in tick-borne and no known vector flaviviruses have distinct characteristics and their 3-D fold was unsolved. To address this, we identified subgenomic flaviviral RNA formation in the encephalitis-causing tick-borne Powassan Virus. We characterized their secondary structure using chemical probing and solved the structure of one of its xrRNAs using cryo-EM. This structure reveals a novel double loop ring element leading to a model in which the ring is remodeled upon encountering the exoribonuclease. Using bioinformatic analyses we showed that this structure is representative of a broad class of xrRNAs and defined key structural and sequence determinants of function. These discoveries reveal a conserved strategy of structure-based exoribonuclease resistance achieved through a unique topology across a viral family of key importance to global health.

microbiology↗

bioRxiv2023

Diversity and modularity of tyrosine-accepting tRNA-like structures

Certain positive-sense single-stranded RNA viruses contain elements at their 3 termini that structurally mimic tRNAs. These tRNA-like structures (TLSs) are classified based on which amino acid is covalently added to the 3 end by host aminoacyl-tRNA synthetase. Recently, a cryoEM reconstruction of a representative tyrosine-accepting tRNA-like structure (TLSTyr) from brome mosaic virus (BMV) revealed a unique mode of recognition of the viral anticodon-mimicking domain by tyrosyl-tRNA synthetase. Some viruses in the hordeivirus genus of Virgaviridae are also selectively aminoacylated with tyrosine, yet these TLS RNAs have a different architecture in the 5 domain that comprises the atypical anticodon loop mimic. Herein, we present bioinformatic and biochemical data supporting a distinct secondary structure for the 5' domain of the hordeivirus TLSTyr compared to those in Bromoviridae. Despite forming a different secondary structure, the 5' domain is necessary to achieve robust in vitro aminoacylation. Furthermore, a chimeric RNA containing the 5' domain from the BMV TLSTyr and the 3' domain from a hordeivirus TLSTyr are aminoacylated, illustrating modularity in these structured RNA elements. We propose that the structurally distinct 5' domain of the hordeivirus TLSTyrs performs the same role in mimicking the anticodon loop as its counterpart in the BMV TLSTyr. Finally, these structurally and phylogenetically divergent types of TLSTyr provide insight into the evolutionary connections between all classes of viral tRNA-like structures.

biochemistry↗

bioRxiv2020

An Expanded Class of Histidine-Accepting Viral tRNA-like Structures

Structured RNA elements are common in the genomes of RNA viruses, often playing critical roles during viral infection. Some RNA elements use forms of tRNA mimicry, but the diverse ways this mimicry can be achieved are poorly understood. Histidine-accepting tRNA-like structures (TLSHis) are examples found at the 3' termini of some positive-sense single-stranded RNA (+ssRNA) viruses where they interact with several host proteins, induce histidylation of the RNA genome, and facilitate several processes important for infection, to include replication. As only five TLSHis examples had been reported, we explored the possible larger phylogenetic distribution and diversity of this TLS class using bioinformatic approaches. We identified many new examples of TLSHis, yielding a rigorous consensus sequence and secondary structure model that we validated by chemical probing of representative TLSHis RNAs. We confirmed new examples as authentic TLSHis by demonstrating their ability to be histidylated in vitro, then used mutational analyses to verify a tertiary interaction that is likely analogous to the D- and T-loop interaction found in canonical tRNAs. These results expand our understanding of how diverse RNA sequences achieve tRNA-like structures and functions in the context of viral RNA genomes and lay the groundwork for high-resolution structural studies of tRNA mimicry by histidine-accepting TLSs.

biochemistry↗

bioRxiv2020

Structural Diversity and Phylogenetic Distribution of Valyl tRNA-like Structures in Viruses

Viruses commonly use specifically folded RNA elements that interact with both host and viral proteins to perform functions important for diverse viral processes. Examples are found at the 3' termini of certain positive-sense ssRNA virus genomes where they partially mimic tRNAs, including being aminoacylated by host cell enzymes. Valine-accepting tRNA-like structures (TLSVal) are an example that share some clear homology to canonical tRNAs but have several important structural differences. Although many examples of TLSVal have been identified, we lacked a full understanding of their structural diversity and phylogenetic distribution. To address this, we undertook an in-depth bioinformatic and biochemical investigation of these RNAs, guided by recent high-resolution structures of a TLSVal. We cataloged many new examples in plant-infecting viruses but also in unrelated insect-specific viruses. Using biochemical and structural approaches, we verified the secondary structure of representative TLSVal substrates and tested their ability to be valylated, finding structural heterogeneity within this class. In a few cases, large stem-loop structures are inserted within distinct variable regions located in an area of the TLS distal to known host cell factor binding sites. In addition, we identified one virus whose TLS has switched its anticodon away from valine; the implications of this remain unclear. These results refine our understanding of the structural and functional mechanistic details of tRNA mimicry and how this may be used in viral infection.

biochemistry↗