Biology subjects

Lulla, V.

Publications and source records attributed to Lulla, V..

12 recordsLinked to original sources

bioRxiv2026

Herpes simplex virus pUL56 abolishes neuronal activity by removing voltage-gated ion channels from the plasma membrane

Herpes simplex virus 1 (HSV-1) infections of the central nervous system cause encephalitis and are associated with increased risk of neurodegeneration, yet the molecular consequences of lytic infection in human neurones remain incompletely defined. We map the transcriptomic, proteomic and surface-proteome changes induced by HSV-1 across the lytic infection cycle in human iPSC-derived cortical glutamatergic neurones. HSV-1 drives extensive plasma-membrane remodelling, including the removal of voltage-gated sodium, potassium and calcium channels, resulting in a profound loss of synchronous calcium signalling. We identify the viral ubiquitin-ligase adaptor pUL56 as the principal effector of this process: pUL56-dependent depletion of ion channels abolishes coordinated calcium signalling, whereas deletion or mutation of its E3-ligase binding motifs preserves synchrony. Furthermore, expression of pUL56 alone is sufficient to abolish neuronal electrical activity. These findings establish pUL56 as a potent viral suppressor of neuronal excitability and provide potential mechanistic links between HSV-1 infection and neurodegenerative pathology.

microbiology↗

bioRxiv2026

The dynamics and strategy of RNA replication in astroviruses

Astroviruses are positive-sense single-stranded RNA viruses that cause significant disease across avian and mammalian hosts, yet their replication mechanisms remain poorly understood. The replication of astrovirus RNA occurs via a double-stranded RNA intermediate that is used as a template for the synthesis of new positive-sense RNA, which is covalently linked to the virus-encoded protein VPg. These viruses also produce a capsid-encoding subgenomic (sg) RNA that is 3'-coterminal with the genomic RNA. The mechanisms by which the astrovirus sgRNA is produced and regulated during infection have not yet been characterized. Using high throughput sequencing of RNA from cells infected with each of five different astrovirus strains, we demonstrate that the presence of a (-)sgRNA is a conserved feature of infection, supporting a premature termination model of subgenomic RNA production. A pronounced pile-up in the mapping positions of the 3' ends of negative-sense RNA reads marks the precise 3' terminus of the (-)sgRNA. We investigate the relative abundance and dynamics of positive and negative RNA species during virus replication and virion packaging, and perform a mutational analysis of conserved residues in the genomic and subgenomic 5' termini. Together, this work elucidates the dynamics of genomic and subgenomic RNA synthesis during astrovirus infection. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=70 SRC="FIGDIR/small/700307v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@1d71111org.highwire.dtl.DTLVardef@a1a024org.highwire.dtl.DTLVardef@118d126org.highwire.dtl.DTLVardef@4b3c4e_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

Viral protease-mediated polyprotein processing in human astroviruses

Positive-sense RNA viruses often encode large polyproteins that are proteolytically processed by viral and host proteases into functional replication proteins. Astroviruses infect intestinal and neuronal cells across diverse human and animal hosts and also rely on polyprotein cleavage for replication. In this study, we mapped the cleavage sites of the nonstructural polyproteins of classical human astrovirus 1 (HAstV1) and neurotropic astrovirus strain MLB2 using complementary N-terminomics of infected cells and analyses of untagged overexpressed polyproteins. Notably, we identified two adjacent cleavage sites at the N-terminus of HAstV1 and MLB2 proteases, as well as a similar dual cleavage site at the C-terminus of the MLB2 protease. We also demonstrated processing of the hypervariable region and VPg in both astrovirus strains. This allowed us to define the boundaries of individual protein products and identify conserved and divergent processing features between classical and non-classical astroviruses. Additionally, we characterized several polyprotein precursors and evaluated the replication properties of cleavage-deficient mutant replicons, revealing the critical role of polyprotein processing for functional replication complex formation. Understanding the dynamics of polyprotein processing is essential for interpreting the stages of viral infection and identifying new drug targets and antiviral strategies.

microbiology↗

bioRxiv2025

ZNFX1, an immunoregulatory RNA helicase and E3 ubiquitin ligase, assembles into pleiomorphic polymers

ZNFX1 is an SF1-family RNA helicase essential for innate immunity. Patients with ZNFX1 mutations experience recurrent infections, yet the underlying mechanism remains unclear. We determined cryo-EM structures of ZNFX1 in apo and RNA-bound forms, revealing auto-inhibition of the helicase through a regulatory insertion occluding the RNA-binding groove. ZNFX1 also functions as a bi-catalytic E3 ubiquitin ligase, containing an RZ-finger homologous to RNF213 and a previously unidentified Miz-like domain that catalyze ubiquitylation independently or cooperatively, with activity enhanced by ubiquitin chains. Patient mutations demonstrate that the helicase, E3 ligase, and rigid zinc-finger stalk connecting them are required for function. ZNFX1 can assemble into structured, pleiomorphic polymers via multivalent protein-protein interactions, revealing a mechanism that may facilitate RNA sequestration in stress granules and antiviral activity. These findings establish ZNFX1 as a multifunctional enzyme in innate immunity that couples RNA sensing to ubiquitin signaling and assembles into higher-order structures for signal amplification.

biochemistry↗

bioRxiv2025

Structural and mechanistic insights into translation initiation on the enterovirus Type 1 IRES

Enteroviruses are a diverse group of pathogens that cause over one billion human infections annually. Upon cell entry, translation of the viral genome is directed by an internal ribosome entry site (IRES) within the 5' untranslated region. Despite early identification of the Type 1 poliovirus IRES, the structural and mechanistic basis for its activity remains poorly understood due to its size, flexibility and dependence on multiple host cell factors. Here, we reconstitute human translation initiation on a model poliovirus IRES and examine 48S complexes by cryo-electron microscopy. Our structures reveal how IRES domain IVc contacts ribosomal proteins uS19 and uS13, whilst a conserved GNRA tetraloop engages with the initiator tRNA during start-codon recognition. Disruption of these interfaces impairs IRES-dependent translation and viral replication. Together, our results provide new structural and mechanistic insights into initiation on the Type 1 IRES and reveal conserved RNA-RNA interactions critical for enterovirus translation.

molecular biology↗

bioRxiv2025

Flexibility and modulation of translation initiation in enterovirus genomes

Enteroviruses comprise a large group of mammalian pathogens that often utilize two open reading frames (ORFs) to encode their proteins: the upstream protein (UP) and the main polyprotein. In some enteroviruses, in addition to the canonical upstream AUG (uAUG), there is another AUG that may represent an alternative upstream initiation site. An analysis of enterovirus sequences containing additional upstream AUGs identified several clusters, including strains of pathogenic Enterovirus alphacoxsackie and E. coxsackiepol. Using ribosome profiling on coxsackievirus CVA-13 (E. coxsackiepol), we demonstrate that both upstream AUG codons can be used for translation initiation in infected cells. Moreover, we confirm translation from both upstream AUGs using a reporter system. Mutating the additional upstream AUG in the context of CVA-13 did not result in phenotypic changes in immortalized cell lines. However, the wild-type virus outcompeted this mutant in human intestinal organoids and differentiated neuronal systems, representing an advantage in physiologically relevant infection sites. Mutation of the stop codon of the shorter upstream ORF led to dysregulated translation of the other ORFs in the reporter system, suggesting a potential role for the additional uORF in modulating the expression level of the other ORFs. These findings demonstrate the remarkable plasticity of enterovirus IRES-mediated initiation and the competitive advantage of double-upstream-AUG-containing viruses in terminally differentiated intestinal organoids and neuronal systems.

microbiology↗

bioRxiv2024

The astrovirus N-terminal nonstructural protein anchors replication complexes to the perinuclear ER membranes

An essential aspect of viral replication is the anchoring of the replication complex (RC) to cellular membranes. Positive-sense RNA viruses employ diverse strategies, including co-translational membrane targeting through signal peptides and co-opting cellular membrane trafficking components. Often, N-terminal nonstructural proteins play a crucial role in linking the RC to membranes, facilitating the early association of the replication machinery. Astroviruses utilize a polyprotein strategy to synthesize nonstructural proteins, relying on subsequent processing to form replication-competent complexes. In this study, we provide evidence for the perinuclear ER membrane association of RCs in five distinct human astrovirus strains. Using tagged recombinant classical human astrovirus 1 and neurotropic MLB2 strains, we establish that the N-terminal domain guides the ER membrane association. Through mutational analysis of the N-terminal domain in replicon and reverse genetics systems, we identified di-arginine motifs responsible for the perinuclear ER retention and formation of functional RCs. Our findings highlight the intricate virus-ER interaction mechanism employed by astroviruses, potentially leading to the development of novel antiviral intervention strategies. Author SummaryHuman astroviruses are a significant cause of acute gastroenteritis, accounting for up to 9% of cases in young children. Immunocompromised individuals and infants experience more critical symptoms, such as severe and persistent diarrhea, as well as sporadic systemic and even fatal diseases. To date, no drugs have been developed to protect against astrovirus infection. Our study provides the first evidence that the integrity of the N-terminal domain of nsP1a is essential for establishing early replication. Central to this process, the di-arginine motifs in the N-terminal domain are responsible for ER retention, the formation of functional replication complexes, and viral replication. Therefore, selectively targeting N-terminal domain-mediated ER retention could be a promising therapeutic strategy to effectively control astrovirus infection.

microbiology↗

bioRxiv2022

The SARS-CoV-2 protein ORF3c is a mitochondrial modulator of innate immunity

The SARS-CoV-2 genome encodes a multitude of accessory proteins. Using comparative genomic approaches, an additional accessory protein, ORF3c, has been predicted to be encoded within the ORF3a sgmRNA. Expression of ORF3c during infection has been confirmed independently by ribosome profiling. Despite ORF3c also being present in the 2002-2003 SARS-CoV, its function has remained unexplored. Here we show that ORF3c localises to mitochondria during infection, where it inhibits innate immunity by restricting IFN-{beta} production, but not NF-{kappa}B activation or JAK-STAT signalling downstream of type I IFN stimulation. We find that ORF3c acts after stimulation with cytoplasmic RNA helicases RIG-I or MDA5 or adaptor protein MAVS, but not after TRIF, TBK1 or phospho-IRF3 stimulation. ORF3c co-immunoprecipitates with the antiviral proteins MAVS and PGAM5 and induces MAVS cleavage by caspase-3. Together, these data provide insight into an uncharacterised mechanism of innate immune evasion by this important human pathogen.

microbiology↗

bioRxiv2022

Attenuation hotspots in neurotropic human astroviruses

During the last decade, the detection of neurotropic astroviruses has increased dramatically. The MLB genogroup of astroviruses represents a genetically distinct group of zoonotic astroviruses associated with gastroenteritis and severe neurological complications in young children, the immunocompromised and the elderly. Using different virus evolution approaches, we identified dispensable regions in the 3' end of the capsid-coding region responsible for attenuation of MLB astroviruses in susceptible cell lines. To create recombinant viruses with identified deletions, MLB reverse genetics and replicon systems were developed. Recombinant truncated MLB viruses had wild type-like or enhanced growth and replication properties in permissive cells but were strongly attenuated in iPSC-derived neuronal cultures confirming the location of neurotropism determinants. This approach can be used for the development of vaccine candidates using attenuated astroviruses that infect humans, livestock animals and poultry.

microbiology↗

bioRxiv2022

The highly conserved stem-loop II motif is important for the lifecycle of astroviruses but dispensable for SARS-CoV-2

The stem-loop II motif (s2m) is an RNA element present in viruses from divergent viral families, including astroviruses and coronaviruses, but its functional significance is unknown. We created deletions or substitutions of the s2m in astrovirus VA1 (VA1), classic human astrovirus 1 (HAstV1) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). For VA1, recombinant virus could not be rescued upon partial deletion of the s2m or substitutions of G-C base pairs. Compensatory substitutions that restored the G-C base-pair enabled recovery of VA1. For HAstV1, a partial deletion of the s2m resulted in decreased viral titers compared to wild-type virus, and reduced activity in a replicon system. In contrast, deletion or mutation of the SARS-CoV-2 s2m had no effect on the ability to rescue the virus, growth in vitro, or growth in Syrian hamsters. Our study demonstrates the importance of the s2m is virus-dependent.

microbiology↗

bioRxiv2020

Antisense oligonucleotides target a nearly invariant structural element from the SARS-CoV-2 genome and drive RNA degradation

RNA structural elements occur in numerous single stranded (+)-sense RNA viruses. The stemloop 2 motif (s2m) is one such element with an unusually high degree of sequence conservation, being found in the 3 UTR in the genomes of many astroviruses, some picornaviruses and noroviruses, and a variety of coronaviruses, including SARS-CoV and SARS-CoV-2. The evolutionary conservation and its occurrence in all viral subgenomic transcripts implicates a key role of s2m in the viral infection cycle. Our findings indicate that the element, while stably folded, can nonetheless be invaded and remodelled spontaneously by antisense oligonucleotides (ASOs) that initiate pairing in exposed loops and trigger efficient sequence-specific RNA cleavage in reporter assays. ASOs also act to inhibit replication in an astrovirus replicon model system in a sequence-specific, dose-dependent manner and inhibit SARS-CoV-2 infection in cell culture. Our results thus permit us to suggest that the s2m element is a site of vulnerability readily targeted by ASOs, which show promise as anti-viral agents.

molecular biology↗

bioRxiv2019

A hidden gene in astroviruses encodes a cell-permeabilizing protein involved in virus release

Human astroviruses are small nonenveloped viruses with positive-sense single-stranded RNA genomes that contain three main open reading frames: ORF1a, ORF1b and ORF2. Astroviruses cause acute gastroenteritis in children worldwide and have been associated with encephalitis and meningitis in immunocompromised individuals. Through comparative genomic analysis of >400 astrovirus sequences, we identified a conserved \"ORFX\" overlapping the capsid-encoding ORF2 in genogroup I, III and IV astroviruses. ORFX appears to be subject to purifying selection, consistent with it encoding a functional protein product, termed XP. Using ribosome profiling of cells infected with human astrovirus 1, we confirm initiation at the ORFX AUG. XP-knockout astroviruses are strongly attenuated and after passaging can partly restore viral titer via pseudo-reversions, thus demonstrating that XP plays an important role in virus growth. To further investigate XP, we developed an astrovirus replicon system. We demonstrate that XP has only minor effects on RNA replication and structural protein production. Instead, XP associates with the plasma membrane with an extracellular N-terminus topology and promotes efficient virus release. Using two different assays, we show that expression of human or related astrovirus XPs leads to cell permeabilization, suggesting a viroporin-like activity. The discovery of XP advances our knowledge of these important human viruses and opens a new direction of research into astrovirus replication and pathogenesis.

microbiology↗