Biology subjects

Vicens, Q.

Publications and source records attributed to Vicens, Q..

14 recordsLinked to original sources

bioRxiv2026

Shifu: an integrated framework for deep learning of RNA secondary structure

Deep learning has advanced RNA secondary-structure prediction by bypassing explicit energy rules to capture long-range dependencies, yet progress is limited less by model scale than by how structures are measured: single scores hide where and why models fail, and benchmark scores can reflect memorization of one dataset rather than genuine generalization. We address this with Shifu, a framework of three coupled parts. Shifu-Corpus is a leakage-audited dataset of 254123 sequences from six databases, with family-aware splits certified free of exact and near-duplicate leaks. The Shifu Trifecta scores a model on three axes (correctness, breadth across diverse RNAs, and whether its confidence can be trusted) rather than one number. Shifu-LMR, a family of compact RNA language models, serves as controlled experiments: changing the training corpus shifts accuracy by 0.13, and a 65-million-parameter model, Shifu-LMR-Nano, leads on correctness while running on a laptop. We release the dataset, code, and model backbones.

bioinformatics↗

bioRxiv2026

elDORS: An elevated Database Of RNA Sequences

Massive and integrated sequence databases have revolutionized computational protein structure prediction. RNA lags due to a lack of consolidated sequence resources. To bridge this gap, we developed elDORS_raw, which comprises up-to-date sequence information, including recent metagenomes and transcriptome sequence data. We optimized an 80% sequence-identity clustered version named elDORS for use with the RNAcmap3 split-strategy for multiple sequence alignment (MSA) and the widely used rMSA pipeline. Our benchmarking demonstrates that elDORS-augmented MSA pipelines match or exceed the alignment depth obtained with massive legacy databases across different queries, including blind CASP challenges, effectively eliminating sequence retrieval failures challenging orphan RNAs. To aid homology searches, predicting RNA properties, training new models, and other downstream tasks, elDORS is freely accessible. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=197 HEIGHT=200 SRC="FIGDIR/small/737016v1_ufig1.gif" ALT="Figure 1"> View larger version (57K): org.highwire.dtl.DTLVardef@d7549aorg.highwire.dtl.DTLVardef@f36ab1org.highwire.dtl.DTLVardef@e1a07eorg.highwire.dtl.DTLVardef@efdab4_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

bioRxiv2026

ZBP1's Inability to Convert Unmodified RNAs to the Z-form Underlies a Balanced Mechanism of RNA Recognition with ADAR1

Z-DNA Binding Protein 1 (ZBP1) is a critical pattern recognition receptor within the innate immune response to viral infection. ZBP1 senses foreign nucleic acids in the unusual, left-handed Z-conformation via binding through its N-terminal Z1 and Z2 domains and activates downstream pro-pyroptotic, -apoptotic, and -necroptotic pathways to initiate cell death and allow for viral clearance. Both dsDNA and dsRNA can adopt the Z-conformation, however, the conformational change is energetically expensive, especially for dsRNA, and typically requires chemical modifications or protein binding to induce a right-to-left-handed conversion and stabilization. ZBP1 has been previously shown to bind and convert B-DNA to the Z-conformation and was assumed to be able to convert A-RNA as well, despite the lack of experimental validation. Here, we use a variety of Nuclear Magnetic Resonance (NMR) and other biophysical and biochemical experiments to characterize the Z-DNA and Z-RNA binding properties of ZBP1s Z1 and Z2 domains. While ZBP1s Z domains are able to convert and stabilize unmodified dsDNA in the Z-conformation, both domains are incapable of flipping unmodified A-conformation dsRNA. We show that ZBP1s Z domains require dsRNAs with Z-promoting chemical modification in order for them to bind and stabilize the Z-conformation. These results contrast with the Z domain from Adenosine Deaminase Acting on RNA 1 (ADAR1), which can bind and flip both dsDNA and dsRNA into the Z-conformation, potentially indicating finely tuned competition between ADAR1 and ZBP1 for pro-survival and pro-death outcomes, respectively. This work highlights the functional variability of Z domains and narrows down the potential physiological substrates of ZBP1 in infection and disease. Graphical O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=81 SRC="FIGDIR/small/719927v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@11a03caorg.highwire.dtl.DTLVardef@eec771org.highwire.dtl.DTLVardef@67d152org.highwire.dtl.DTLVardef@1df808d_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2025

Cryo-EM structures of anti Z-DNA antibodies in complex with antigen reveal distinct recognition modes of a left-handed geometry

Double-stranded nucleic acids can undergo transitions from canonical B/A-forms to alternate left-handed Z-DNA/Z-RNA (Z-NAs). Z-NAs are implicated in processes such as neuroinflammation in Alzheimers disease, Lupus Erythematosus, microbial biofilms, and type I interferon-mediated human pathologies. Since endogenous Z-NA sensors like the Z domain can induce B-to-Z transitions, monoclonal antibodies (mAbs) Z-D11 and Z22 have been regarded as conformation-specific tools to confirm Z-NA in situ, although high-resolution structural information is missing. Here, we employed single-particle cryo-electron microscopy to solve structures of Z-D11 and Z22 bound to synthetic d(CG)6 12mer Z-DNA duplex. Both mAbs form filamentous trimers around the Z-DNA axis, further stabilized by Fab-Fab interactions. The mAbs achieve specificity through extensive contacts to both Z-form backbone strands and the exposed guanine/cytosine bases in the major groove. This mode of recognition is dictated by shape complementarity rather than sequence specificity, sensing the alternating syn/anti backbone torsions and the phosphate zig-zag geometry unique to Z-DNA. Our data also suggest that these mAbs are not inducing B-to-Z transitions under normal physiological conditions. Finally, comparison to other double-stranded NA-binding mAbs defines a similar structural logic adapted to different helical geometry recognition patterns, thus providing a framework for engineering highly specific nucleic acid probes.

biochemistry↗

bioRxiv2025

Z-Form Stabilization By The Zα Domain Of Adar1p150 Has Subtle Effects On A-To-I Editing

The role of Adenosine Deaminase Acting on RNA 1 (ADAR1)s Z-conformation stabilizing Z domain in A-to-I editing is unclear. Previous studies on Z mutations faced limitations, including variable ADAR1p150 expression, differential editing analysis challenges, and unaccounted changes in ADAR1p150 localization. To address these issues, we developed a Cre-lox system in ADAR1p150 KO cells to generate stable cell lines expressing Z mutant ADAR1p150 constructs. Using total RNA sequencing analyzing editing clusters as a proxy for dsRNAs, we found that Z mutations slightly decreased overall A-to-I editing, consistent with recent findings. These decreases correlated with mislocalization of ADAR1p150 rather than reduced editing specificity, and practically no statistically significant differentially edited sites were identified between wild-type and Z mutant ADAR1p150 constructs. These results suggest that Zs impact on editing is minor and that phenotypes in Z mutant mouse models and human patients may arise from editing-independent inhibition of Z-DNA-Binding Protein 1 (ZBP1), rather than changes in RNA editing.

cell biology↗

bioRxiv2025

RNAhub - an automated pipeline to search and align RNA homologs with secondary structure assessment

The complexity in the generation of RNA multiple sequence alignments and assessment of the accuracy of such alignments contributes to the challenges in the utilization of RNA alignments in diverse integrative methods. RNAhub is a freely available user-friendly web server for a reliable generation of RNA multiple sequence alignments and the detection of the presence of structural RNA utilizing evolutionary information. This web-based tool, developed by the integration of existing computational approaches, takes an RNA sequence as input and automatically retrieves and aligns sequences homologous to the input (query) RNA sequence through an iterative and structure-agnostic approach. Based on the alignment, this tool statistically assesses whether the query RNA sequence has a conserved RNA structure using covariation analysis. The web server allows the user to efficiently search the sequence of interest against carefully curated, ready-to-use genomic databases to produce a multiple sequence alignment. Using this alignment, our tool either detects the presence of a conserved structural RNA, finds evidence against the presence of a conserved structure, or cannot make any assessment due to a lack of sequence diversity in the alignment. The web server is freely available at https://rnahub.org. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=181 HEIGHT=200 SRC="FIGDIR/small/642701v3_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@540f6forg.highwire.dtl.DTLVardef@c15e53org.highwire.dtl.DTLVardef@117ced2org.highwire.dtl.DTLVardef@b679c_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

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↗

bioRxiv2022

Cryo-EM reveals an entangled kinetic trap in the folding pathway of a catalytic RNA

Functional RNAs fold through complex pathways that can contain misfolded "kinetic traps." A complete model of RNA folding requires understanding the formation of such misfolded states, but they are difficult to characterize due to their transient and potentially conformationally dynamic nature. We used cryo-electron microscopy (cryo-EM) to visualize a long-lived misfolded state in the folding pathway of the Tetrahymena thermophila group I intron, a paradigmatic RNA structure-function model system. The structure revealed how this state forms native-like secondary structure and tertiary contacts but contains two incorrectly crossed strands, consistent with a previous model. This incorrect topology mispositions a critical catalytic domain and cannot be resolved locally, as extensive refolding is required. This work provides a structural framework for interpreting decades of biochemical and functional studies and demonstrates the power of cryo-EM for the exploration of RNA folding pathways.

biochemistry↗

bioRxiv2020

The Halastavi arva virus intergenic region IRES promotes translation by the simplest possible initiation mechanism

Dicistrovirus intergenic region internal ribosomal entry sites (IGR IRES) do not require initiator tRNA, an AUG codon or initiation factors, and jumpstart translation from the middle of the elongation cycle via formation of IRES/80S complexes resembling the pre-translocation state. eEF2 then translocates the [codon-anticodon]-mimicking pseudoknot I (PKI) from ribosomal A to P sites, bringing the first sense codon into the decoding center. Halastavi arva virus (HalV) contains an IGR that is related to previously described IGR IRESs, but lacks domain 2, which enables these IRESs to bind to individual 40S ribosomal subunits. By employing in vitro reconstitution and cryo-electron microscopy, we now report that the HalV IGR IRES functions by the simplest initiation mechanism that involves binding to 80S ribosomes such that PKI is placed in the P site, so that the A site contains the first codon that is directly accessible for decoding without prior eEF2-mediated translocation of PKI.

molecular biology↗

bioRxiv2020

Different tertiary interactions create the same important 3-D features in a divergent flavivirus xrRNA

During infection by a flavivirus (FV), cells accumulate noncoding subgenomic flavivirus RNAs (sfRNAs) that interfere with several antiviral pathways. These sfRNAs are formed by structured RNA elements in the 3' untranslated region (UTR) of the viral genomic RNA, which block the progression of host cell exoribonucleases that have targeted the viral RNA for destruction. Previous work on these exoribonuclease-resistant RNAs (xrRNAs) from mosquito-borne FVs revealed a specific 3-dimensional fold with a unique topology in which a ring-like structure protectively encircles the 5' end of the xrRNA. Conserved nucleotides make specific tertiary interactions that support this fold. Examination of more divergent FVs reveals differences in their 3' UTR sequences, raising the question of whether they contain xrRNAs and if so, how they fold. To answer this, we demonstrated the presence of an authentic xrRNA in the 3' UTR of the Tamana Bat Virus (TABV) and solved its structure by x-ray crystallography. The structure reveals conserved features from previously characterized xrRNAs, but in the TABV version these features are created through a novel set of tertiary interactions not previously seen in xrRNAs. This includes two important A-C interactions, four distinct backbone kinks, several ordered Mg2+ ions, and a C+-G-C base triple. The discovery that the same overall architecture can be achieved by very different sequences and interactions in distantly related flaviviruses provides insight into the diversity of this type of RNA and will inform searches for undiscovered xrRNAs in viruses and beyond.

biochemistry↗

bioRxiv2020

A new subclass of exoribonuclease resistant RNA found in multiple Flaviviridae genera

Viruses have developed innovative strategies to exploit the cellular machinery and overcome the host antiviral defenses, often using specifically structured RNA elements. Examples are found in flaviviruses; during flaviviral infection, pathogenic subgenomic flaviviral RNAs (sfRNAs) accumulate in the cell. These sfRNAs are formed when a host cell 5 to 3 exoribonuclease degrades the viral genomic RNA but is blocked by an exoribonuclease resistant RNA structure (xrRNA) located in the viral genomes 3untranslated region (UTR). Although known to exist in several Flaviviridae genera the full distribution and diversity of xRNAs in this virus family was unknown. Using the recent high-resolution structure of an xrRNA from the divergent flavivirus Tamana bat virus (TABV) as a reference, we used bioinformatic searches to identify xrRNA in the Pegivirus, Pestivirus, and Hepacivirus genera. We biochemically and structurally characterized several examples, determining that they are genuine xrRNAs with a conserved fold. These new xrRNAs look superficially similar to the previously described xrRNAs but possess structural differences making them distinct from previous classes of xrRNAs. Our findings thus require adjustments of previous xrRNA classification schemes and expand on the previously known distribution of the xrRNA in Flaviviridae, indicating their widespread distribution and illustrating their importance. IMPORTANCEThe Flaviviridae comprise one of the largest families of positive sense single stranded (+ssRNA) and it is divided into the Flavivirus, Pestivirus, Pegivirus, and Hepacivirus genera. The genus Flavivirus contains many medically relevant viruses such as Zika Virus, Dengue Virus, and Powassan Virus. In these, a part of the viruss RNA twists up into a very special three-dimensional shape called an xrRNA that blocks the ability of the cell to "chew up" the viral RNA. Hence, part of the virus RNA remains intact, and this protected part is important for viral infection. This was known to occur in Flaviviruses but whether it existed in the other members of the family was not known. In this study, we not only identified a new subclass of xrRNA found in Flavivirus but also in the remaining three genera. The fact that this process of viral RNA maturation exists throughout the entire Flaviviridae family makes it clear that this is an important but underappreciated part of the infection strategy of these diverse human pathogens.

microbiology↗

bioRxiv2020

The crystal structure of a Polerovirus exoribonuclease-resistant RNA shows how diverse sequences are integrated into a conserved fold

Exonuclease-resistant RNAs (xrRNAs) are discrete elements that block the progression of 5 to 3 exonucleases using specifically folded RNA structures. A recently discovered class of xrRNA is widespread in several genera of plant-infecting viruses, within both noncoding and protein-coding subgenomic RNAs. The structure of one such xrRNA from a dianthovirus revealed three-dimensional details of the resistant fold but did not answer all questions regarding the conservation and diversity of this xrRNA class. Here, we present the crystal structure of a representative polerovirus xrRNA that contains sequence elements that diverge from the previously solved structure. This new structure rationalizes previously unexplained sequence conservation patterns and shows interactions not present in the first structure. Together, the structures of these xrRNAs from dianthovirus and polerovirus genera support the idea that these plant virus xrRNAs fold through a defined pathway that includes a programmed intermediate conformation. This work deepens our knowledge of the structure-function relationship of xrRNAs and shows how evolution can craft similar RNA folds from divergent sequences.

biochemistry↗

bioRxiv2018

Pervasiveness of exoribonuclease-resistant RNAs in plant viruses suggests new roles for these conserved RNA structures

Exoribonuclease-resistant RNAs (xrRNAs) are discrete folded RNA elements that block the processive degradation of RNA by exoribonucleases. xrRNAs found in the 3' untranslated regions (UTRs) of animal-infecting flaviviruses and in all three members of the plant-infecting Dianthovirus adopt a complex ring-like fold that blocks the exoribonuclease; this ability gives rise to viral non-coding subgenomic RNAs. The degree to which these folded RNA elements exist in other viruses and in diverse contexts has been unclear. Using computational tools and biochemical assays, we discovered that xrRNA elements are widely found in viruses belonging to the Tombusviridae and Luteoviridae families of plant-infecting RNA viruses, demonstrating their importance and widespread utility. Unexpectedly, many xrRNAs are located in intergenic regions rather than in the 3UTR and some are associated with the 5' ends of subgenomic RNAs with protein-coding potential, suggesting that xrRNAs with similar scaffolds are involved in the maturation or maintenance of diverse subgenomic RNAs, not just the ones generated from the 3'UTR.

microbiology↗

bioRxiv2018

Structure-activity relationship of flavin analogs that target the FMN riboswitch

The flavin mononucleotide (FMN) riboswitch is an emerging target for the development of novel RNA-targeting antibiotics. We previously discovered an FMN derivative --5FDQD-- that protects mice against diarrhea-causing Clostridium difficile bacteria. Here, we present the structure-based drug design strategy that led to the discovery of this fluoro-phenyl derivative with antibacterial properties. This approach involved the following stages: (1) structural analysis of all available free and bound FMN riboswitch structures; (2) design, synthesis and purification of derivatives; (3) in vitro testing for productive binding using two chemical probing methods; (4) in vitro transcription termination assays; (5) resolution of the crystal structures of the FMN riboswitch in complex with the most mature candidates. In the process, we delineated principles for productive binding to this riboswitch, thereby demonstrating the effectiveness of a coordinated structure-guided approach to designing drugs against RNA.\n\nGRAPHICAL ABSTRACT\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=146 SRC=\"FIGDIR/small/389148_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (41K):\norg.highwire.dtl.DTLVardef@f59798org.highwire.dtl.DTLVardef@1b38b02org.highwire.dtl.DTLVardef@6b50faorg.highwire.dtl.DTLVardef@1915fc4_HPS_FORMAT_FIGEXP M_FIG Exploring the chemical structure landscape of FMN riboswitch binders.\n\nC_FIG

biochemistry↗