Biology subjects

Jenni, S.

Publications and source records attributed to Jenni, S..

12 recordsLinked to original sources

bioRxiv2026

Mechanism of membrane perforation in rotavirus cell entry

Cell entry of non-enveloped, animal viruses requires translocation of a macromolecular assembly across a cellular membrane. Double-stranded RNA viruses introduce into the target cell an inner capsid particle that does not uncoat further. Instead, it extrudes capped viral mRNA by virtue of polymerase and capping activities within it. As described here, we used cryogenic electron tomography to visualize the full course of rhesus rotavirus entry, from cell attachment and virion uptake to release of the subviral particle. The cryo-tomograms and subtomogram averaging of classified subparticles link high-resolution structures of the virion and its components with time series from live-cell fluorescence microscopy. We outlined the mechanism of each step in the entry process, including the membrane perforation step that transfers a subviral particle into the cytosol.

cell biology↗

bioRxiv2024

Octahedral small virus-like particles of dengue virus type 2

Flavivirus envelope (E) and precursor M (prM) proteins, when ectopically expressed, assemble into empty, virus-like particles (VLPs). Cleavage of prM to M and loss of the pr fragment converts the VLPs from immature to mature particles, mimicking a similar maturation of authentic virions. Most of the VLPs obtained by prM-E expression are smaller than virions; early, low-resolution cryo-EM studies suggested a simple, 60-subunit, icosahedral organization. We describe here the cryo-EM structure of immature, small VLPs from dengue virus type 2 and show that they have octahedral rather than icosahedral symmetry. The asymmetric unit of the octahedral particle is an asymmetric trimer of prM-E heterodimers, just as it is on icosahedral immature virions; the full, octahedrally symmetric particle thus has 24 such asymmetric trimers, or 72 prM-E heterodimers in all. Cleavage of prM and release of pr generates ovoid, somewhat irregular, mature particles. Previous work has shown that mature smVLPs have fusion properties identical to those of virions, consistent with local, virion-like clustering of 36 E dimers on their surface. The cryo-EM structure and the properties of these VLPs described here relate directly to on-going efforts to use them as vaccine immunogens. IMPORTANCEEctopic expression of flavivirus envelope (E) and precursor M (prM) proteins leads to formation and secretion of empty, virus-like particles (VLPs), which are candidate, non-infectious, virion-like components of flavivirus vaccines. We show that the immature particles of a major class of VLPs -- "small VLPs" (smVLPs), which have smaller diameter than those of virion size, -- are octahedrally (rather than icosahedrally) symmetric, with the same clustering of prM and E, as asymmetric trimers of prM-E heterodimers, found on immature virions. Cleavage of prM and formation of mature, smVLPs yields somewhat irregular, ovoid particles. Design and characterization of VLPs as vaccine components will need to take these properties into account.

microbiology↗

bioRxiv2023

The rotavirus VP5/VP8 conformational transition permeabilizes membranes to Ca2+

Rotaviruses infect cells by delivering into the cytosol a transcriptionally active inner capsid particle (a "double-layer particle": DLP). Delivery is the function of a third, outer layer, which drives uptake from the cell surface into small vesicles from which the DLPs escape. In published work, we followed stages of rhesus rotavirus (RRV) entry by live-cell imaging and correlated them with structures from cryogenic electron microscopy and tomography (cryo-EM and cryo-ET). The virus appears to wrap itself in membrane, leading to complete engulfment and loss of Ca2+ from the vesicle produced by the wrapping. One of the outer-layer proteins, VP7, is a Ca2+-stabilized trimer; loss of Ca2+ releases both outer-layer proteins from the particle. The other outer-layer protein, VP4, activated by cleavage into VP8* and VP5*, is a trimer that undergoes a large-scale conformational rearrangement, reminiscent of the transition that viral fusion proteins undergo to penetrate a membrane. The rearrangement of VP5* thrusts a 250-residue, C-terminal segment of each of the three subunits outward, while allowing the protein to remain attached to the virus particle and to the cell being infected. We proposed that this segment inserts into the membrane of the target cell, enabling Ca2+ to cross. In the work reported here, we show the validity of key aspects of this proposed sequence. By cryo-EM studies of liposome-attached virions ("triple-layer particles": TLPs) and single-particle fluorescence imaging of liposome-attached TLPs, we confirm insertion of the VP4 C-terminal segment into the membrane and ensuing generation of a Ca2+ "leak". The results allow us to formulate a molecular description of early events in entry. We also discuss our observations in the context of other work on double-strand RNA virus entry.

microbiology↗

bioRxiv2023

Helical reconstruction of VP39 reveals principles for baculovirus nucleocapsid assembly

Baculoviruses are insect-infecting pathogens with wide applications as biological pesticides, in vitro protein production vehicles and gene therapy tools. Its cylindrical nucleocapsid, which encapsulates and protects the circular double-stranded viral DNA encoding proteins for viral replication and entry, is formed by the highly conserved major capsid protein VP39. The mechanism for VP39 assembly remains unknown. We determined a 3.2 [A] electron cryomicroscopy helical reconstruction of an infectious nucleocapsid of Autographa californica multiple nucleopolyhedrovirus, revealing how dimers of VP39 assemble into a 14-stranded helical tube. We show that VP39 comprises a unique protein fold conserved across baculoviruses, which includes a Zinc finger domain and a stabilizing intra-dimer sling. Analysis of sample polymorphism revealed that VP39 assembles in several closely-related helical geometries. This VP39 reconstruction reveals general principles for baculoviral nucleocapsid assembly.

biophysics↗

bioRxiv2022

Structures of the Ndc80 complex and its interactions at the yeast kinetochore-microtubule interface

The conserved Ndc80 kinetochore complex, Ndc80c, is the principal link between spindle microtubules and centromere associated proteins during chromosome segregation. We used AlphaFold 2 to obtain structural predictions of the Ndc80 "loop" region and the Ndc80:Nuf2 globular head domains that interact with the Dam1 subunit of the decameric DASH/Dam1 complex (Dam1c). The predictions guided design of constructs that readily yielded crystal structures, essentially congruent with the predicted ones. The Ndc80 "loop" is a stiff, straight -helical "switchback" structure, and flexibility within the long Ndc80c rod occurs instead at a hinge point between the globular head and the loop. Conserved stretches of the Dam1 C terminus bind Ndc80c with a short helix followed by an extended segment such that phosphorylation of Dam1 serines 257, 265, and 292 by the mitotic kinase Ipl1/Aurora B can release this contact during error correction of mis-attached kinetochores. We integrate the structural results presented here into our current molecular model of the kinetochore-microtubule interface. The model illustrates how multiple interactions between Ndc80c, DASH/Dam1c and the microtubule lattice stabilize kinetochore attachments.

biochemistry↗

bioRxiv2022

Visualizing Molecular Interactions that Determine Assembly of a Bullet-Shaped Vesicular Stomatitis Virus Particle

Vesicular stomatitis virus (VSV) is a negative-strand RNA virus with a non-segmented genome, closely related to rabies virus. Both have characteristic bullet-like shapes. We report the structure of intact, infectious VSV particles determined by cryogenic electron microscopy. By compensating for polymorphism among viral particles with computational classification, we obtained a reconstruction of the shaft ("trunk") at 3.5 [A] resolution, with lower resolution for the rounded tip. The ribonucleoprotein (RNP), genomic RNA complexed with nucleoprotein (N), curls into a dome-like structure with about eight gradually expanding turns before transitioning into the regular helical trunk. Two layers of matrix (M) protein link the RNP with the membrane. Radial inter-layer subunit contacts are fixed within single RNA-N-M1-M2 modules, but flexible lateral and axial interactions allow assembly of polymorphic virions. Together with published structures of recombinant N in various states, our results suggest a mechanism for membrane- coupled self-assembly of VSV and its relatives.

molecular biology↗

bioRxiv2020

The ancient fusogen EnvP(b)1 is expressed in human tissues and its structure informs the evolution of gammaretrovirus envelope proteins

Host genomes have acquired diversity from viruses through the capture of viral elements, often from endogenous retroviruses (ERVs). These viral elements contribute new transcriptional control elements and new protein encoding genes, and their refinement through evolution can generate novel physiological functions for the host. EnvP(b)1 is an endogenous retroviral envelope gene found in human and other primate genomes. We show that EnvP(b)1 arose very early in the evolution of primates, i.e. at least 40-47 million years ago, but has nevertheless retained its ability to fuse primate cells. We have detected similar sequences in the genome of a lemur species, suggesting that a progenitor virus may have circulated 55+ million years ago. We demonstrate that EnvP(b)1 protein is expressed in multiple human tissues and is fully processed, rendering it competent to fuse cells. This activated fusogen is expressed in multiple healthy human tissues and is under purifying selection, suggesting that its expression is selectively advantageous. We determined a structure of the inferred receptor binding domain of human EnvP(b)1, revealing close structural similarities between this Env protein and those of currently circulating leukemia viruses, despite poor sequence conservation. This observation highlights a common scaffold from which novel receptor binding specificities have evolved. The evolutionary plasticity of this domain may underlie the diversity of related Envs in circulating viruses and coopted elements alike. The function of EnvP(b)1 in primates remains unknown. SIGNIFICANCE STATEMENTOrganisms can access genetic and functional novelty by capturing viral elements within their genomes, where they can evolve to drive new cellular or organismal processes. We demonstrate that a retrovirus envelope gene, EnvP(b)1, has been maintained as a functional protein for 40 to [≥]55 million years and is expressed as a protein in multiple healthy human tissues. We believe it has an unknown function in primates. We determined the structure of its inferred receptor binding domain and compared it with the same domain in modern viruses. We find a common conserved architecture that underlies the varied receptor binding activity of divergent Env genes. The modularity and versatility of this domain may underpin the evolutionary success of this clade of fusogens.

microbiology↗

bioRxiv2019

Single cell tri-channel-processing reveals structural variation landscapes and complex rearrangement processes

Structural variation (SV), where rearrangements delete, duplicate, invert or translocate DNA segments, is a major source of somatic cell variation. It can arise in rapid bursts, mediate genetic heterogenity, and dysregulate cancer-related pathways. The challenge to systematically discover SVs in single cells remains unsolved, with copy-neutral and complex variants typically escaping detection. We developed single cell tri-channel-processing (scTRIP), a computational framework that jointly integrates read depth, template strand and haplotype phase to comprehensively discover SVs in single cells. We surveyed SV landscapes of 565 single cell genomes, including transformed epithelial cells and patient-derived leukemic samples, and discovered abundant SV classes including inversions, translocations and large-scale genomic rearrangements mediating oncogenic dysregulation. We dissected the molecular karyotype of the leukemic samples and examined their clonal structure. Different from prior methods, scTRIP also enabled direct detection and discrimination of SV mutational processes in individual cells, including breakage-fusion-bridge cycles. scTRIP will facilitate studies of clonal evolution, genetic mosaicism and somatic SV formation, and could improve disease classification for precision medicine.

genomics↗

bioRxiv2019

Structure of a rabies virus polymerase complex from electron cryo-microscopy

Non-segmented negative-stranded (NNS) RNA viruses, among them the virus that causes rabies (RABV), include many deadly human pathogens. The large polymerase (L) proteins of NNS-RNA viruses carry all the enzymatic functions required for viral mRNA transcription and replication: RNA polymerization, mRNA capping, cap methylation. We describe here a complete structure of RABV L bound with its phosphoprotein cofactor (P), determined by electron cryo-microscopy at 3.3 [A] resolution. The complex closely resembles vesicular stomatitis virus (VSV) L-P, the one other known full-length NNS-RNA L protein structure, with key local differences (e.g., in L-P interactions). Like the VSV L-P structure, the RABV complex analyzed here represents a pre-initiation conformation. Comparison with the likely elongation state, seen in two partial structures of pneumovirus L-P complexes, suggests differences between priming/initiation and elongation complexes. Analysis of internal cavities within RABV L suggests distinct template and product entry and exit pathways during transcription and replication.

molecular biology↗

bioRxiv2019

Structure of the Vesicular Stomatitis Virus L Protein in Complex with Its Phosphoprotein Cofactor

The large (L) proteins of non-segmented, negative-strand RNA viruses are multifunctional enzymes that produce capped, methylated and polyadenylated mRNAs and replicate the viral genome. A phosphoprotein (P), required for efficient RNA-dependent RNA polymerization from the viral ribonucleoprotein (RNP) template, regulates function and conformation of the L protein. We report the structure of vesicular stomatitis virus L in complex with its P cofactor determined by electron cryomicroscopy at 3.0 [A] resolution, enabling us to visualize bound segments of P. The contacts of three P segments with multiple L domains show how P induces a closed, compact, initiation-competent conformation. Binding of P to L positions its N-terminal domain adjacent to a putative RNA exit channel for efficient encapsidation of newly synthesized genomes with the nucleoprotein and orients its C-terminal domain to interact with the RNP template. The model shows that a conserved tryptophan in the priming loop can support the initiating 5-nucleotide.

molecular biology↗

bioRxiv2019

Structures of the ATP-fueled ClpXP proteolytic machine bound to protein substrate

ClpXP is an ATP-dependent protease in which the ClpX AAA+ motor binds, unfolds, and translocates specific protein substrates into the degradation chamber of ClpP. We present cryo-EM studies of the E. coli enzyme that show how asymmetric hexameric rings of ClpX bind symmetric heptameric rings of ClpP and interact with protein substrates. Subunits in the ClpX hexamer assume a spiral conformation and interact with two-residue segments of substrate in the axial channel, as observed for other AAA+ proteases and protein-remodeling machines. Strictly sequential models of ATP hydrolysis and a power stroke that moves two residues of the substrate per translocation step have been inferred from these structural features for other AAA+ unfoldases, but biochemical and single-molecule biophysical studies indicate that ClpXP operates by a probabilistic mechanism in which five to eight residues are translocated for each ATP hydrolyzed. We propose structure-based models that could account for the functional results.

biophysics↗

bioRxiv2019

In situ structure of rotavirus VP1 RNA-dependent RNA polymerase

Rotaviruses, like other non-enveloped, double-strand RNA (dsRNA) viruses, package an RNA-dependent RNA polymerase (RdRp) with each duplex of their segmented genomes. Rotavirus cell entry results in loss of an outer protein layer and delivery into the cytosol of an intact, inner capsid particle (the \"double-layer particle\" or DLP). The RdRp, designated VP1, is active inside the DLP; each VP1 achieves many rounds of mRNA transcription from its associated genome segment. Previous work has shown that one VP1 molecule lies close to each fivefold axis of the icosahedrally symmetric DLP, just beneath the inner surface of its protein shell, embedded in tightly packed RNA. We have determined a high-resolution structure for the rotavirus VP1 RdRp in situ, by local reconstruction of density around individual fivefold positions. We have analyzed intact virions (\"triple-layer particles\" or TLPs), non-transcribing DLPs and transcribing DLPs. Outer layer dissociation enables the DLP to synthesize RNA, in vitro as well as in vivo, but appears not to induce any detectable structural change in the RdRp. Addition of NTPs, Mg2+, and S-adenosyl methionine, which allows active transcription, results in conformational rearrangements, in both VP1 and the DLP capsid shell protein, that allow a transcript to exit the polymerase and the particle. The position of VP1 (among the five symmetrically related alternatives) at one vertex does not correlate with its position at other vertices. This stochastic distribution of site occupancies limits long-range order in the 11-segment, dsRNA genome.

molecular biology↗