Biology subjects

Clare, D. K.

Publications and source records attributed to Clare, D. K..

5 recordsLinked to original sources

bioRxiv2026

Coronavirus spherules are supported by a novel triple-layer protein lattice

Coronaviruses (CoVs) cause significant disease in humans and animals, with a track-record of cross-species transmission. Despite their global significance, available control strategies are limited, especially for emerging CoVs. A deeper fundamental understanding of the virus life cycle is essential to underpin development of control measures. A critical step of the CoV life cycle is the rearrangement of host cell membranes into replication organelles (ROs). This is conserved across all CoVs and ROs comprise double membrane vesicles (DMVs), the site of viral RNA synthesis, and double membrane spherules. CoV spherules are complex structures requiring both positive and negative curvature of paired membranes so are predicted to have a high energy cost to maintain. To date they have an entirely unknown function. Interestingly, although always present, abundance of spherules in CoV infected cells varies with Betacoronavirus Middle East Respiratory Syndrome coronavirus, Gammacoronavirus infectious bronchitis virus (IBV) and porcine deltacoronavirus in particular producing a considerable number. Here, using cryo-bioimaging we identified for the first time that CoV spherules are embedded with a complex and organised triple-layered protein lattice and that spherules always contain a cargo that appears arranged as a shell inside the vesicle. In addition, we confirmed the presence of a double membrane spanning molecular pore in Gammacoronavirus DMVs and further identified a population of potential DMV formation intermediates. Together, this work provides a foundation for understanding a fundamental yet unresolved aspect of coronavirus replication.

microbiology↗

bioRxiv2026

Structural Dynamics of RNA Polymerase II During Nucleotide Addition Cycle

RNA polymerase II (RNAPII) drives gene expression through iterative nucleotide addition cycles (NACs) comprising translocation, substrate binding, and catalysis. The lack of pre-catalysis and post-catalysis intermediates has precluded a complete mechanistic understanding of the NAC. Here we present 43 cryo-EM structures capturing distinct stages of the S. cerevisiae RNAPII elongation complex (EC) NAC, including previously intractable transition intermediates. We establish a continuous spectrum of RNAPII EC structural dynamics during the NAC, which can be divided into two coordinated phases: a substrate-induced EC tightening phase and a post-catalysis EC relaxation phase. For the substrate-induced EC tightening phase, the substrate binding initiates allosteric conformational changes across the entire RNAPII EC, including TL folding, funnel closure, clamp closure, transcription bubble ordering, and precise alignment of the RNA 3'-end with substrate to form a catalysis-competent configuration. For the post-catalysis EC relaxation phase, we captured the long-sought, short-lived post-catalysis product state and identified a series of intermediates that reveal a reverse conformational transition that facilitates rapid translocation. Together, our findings define a comprehensive structural and dynamic framework for RNAPII NAC, yielding a "molecular movie" of RNAPII in action and revealing a fundamental principle by which the enzyme balances speed and fidelity through coordinated conformational dynamics.

molecular biology↗

bioRxiv2024

EMinsight: a tool to capture cryoEM microscope configuration and experimental outcomes for analysis and deposition.

The widespread adoption of cryoEM technologies for structural biology has pushed the discipline to new frontiers. A significant worldwide effort has refined the Single Particle Analysis (SPA) workflow into a reasonably standardised procedure. Significant investment of development time have been made particularly in sample preparation, microscope data collection efficiency, pipeline analyses and data archiving. The widespread adoption of specific commercial microscopes, software for controlling them and best practises developed at national facilities has also begun to establish a degree of standardisation to data structures coming from the SPA workflow. There is opportunity to capitalise on this moment in the fields maturation, to capture metadata from SPA experiments and correlate this with experimental outcomes, which is presented here in a set of programmes called EMinsight. This tool aims to prototype the framework and types of analyses that could lead to new insights into optimal microscope configurations as well as for defining methods for metadata capture to assist with archiving of cryoEM SPA data. We also envisage this tool to be useful to microscope operators and facilities looking to rapidly generate reports on SPA data collection and screening sessions. SynopsisEMinsight is a Python-based tool for systematically mining metadata from single particle analysis cryoEM experiments. The capture and analysis of metadata facilitates assessment of instrument performance, provides concise reporting of experiment performance and sample quality by analysing preprocessing results, and gathers metadata for deposition. We envisage this approach to benefit the microscope operator, facility managers, database developers and users.

biophysics↗

bioRxiv2022

Cryo-plasma FIB/SEM volume imaging of biological specimens

Serial focussed ion beam scanning electron microscopy (FIB/SEM) enables imaging and assessment of sub-cellular structures on the mesoscale (10 nm to 10 m). When applied to vitrified samples, serial FIB/SEM is also a means to target specific structures in cells and tissues while maintaining constituents hydration shells for in-situ structural biology downstream. However, the application of serial FIB/SEM imaging of non-stained cryogenic biological samples is limited due to low contrast, curtaining and charging artefacts. We address these challenges using a cryogenic plasma FIB/SEM (cryo-pFIB/SEM). We evaluated the choice of plasma ion source and imaging regimes to produce high quality SEM images of a range of different biological samples. Using an automated workflow we produced three dimensional volumes of bacteria, human cells, and tissue, and calculated estimates for their resolution, typically achieving 20 to 50 nm. Additionally, a tag-free tool is needed to drive the application of in situ structural biology towards tissue. The combination of serial FIB/SEM with plasmabased ion sources promises a framework for targeting specific features in bulk-frozen samples (>100 m) to produce lamella for cryogenic electron tomography.

cell biology↗

bioRxiv2020

Assembly intermediates of orthoreovirus captured in the cell

Traditionally molecular assembly pathways for viruses have been inferred from high resolution structures of stable intermediates purified in vitro, and from low resolution images of cell sections as well as from genetic approaches including conditionally lethal mutants. Here, we directly visualise a previously unsuspected single shelled icosahedral intermediate for a mammalian orthoreovirus, in addition to the expected virions, in cryo-preserved infected cells by cryo-electron tomography of cellular lamellae1,2. Particle classification and averaging yielded structures at resolutions as high as 5.6 [A], sufficient to identify secondary structural elements and place known molecular structures, allowing us to produce an atomic model of the intermediate, comprising 120 copies of protein {lambda}1 and 120 copies of {sigma}2. This {lambda}1 shell is in a collapsed form compared to the mature virions, with the molecules pushed inwards at the icosahedral 5-folds by ~100 [A]. This grossly indented shell, although produced by a mammalian reovirus, is reminiscent of the first assembly intermediate of prokaryotic dsRNA viruses belonging to a different virus family3, adding weight to the supposition that these diverse viruses share a common ancestor, and suggesting mechanisms for the assembly of viruses of the Reoviridae. Such methodology holds enormous promise for the dissection of the replication cycle of many viruses.

microbiology↗