Biology subjects

Huet, A.

Publications and source records attributed to Huet, A..

7 recordsLinked to original sources

bioRxiv2025

Structural insights into scaffold-guided assembly of the Pseudomonas phage D3 capsid

Tailed bacteriophages comprise the largest structural family of viruses with close relatives in archaea and the eukaryotic herpesviruses. The common assembly pathway produces an icosahedrally symmetric protein shell, called capsid, into which the double-stranded DNA genome is packaged. While capsid sizes and amino acid sequences vary considerably, the major capsid protein (MCP) folds are remarkably similar throughout the family. To investigate the mechanisms governing capsid size, we characterized the procapsid and mature capsid of phage D3, which expresses an icosahedral lattice with Triangulation number T=9. We found that the MCP scaffold domain binds to the interior capsid surface, acting as a clamp to constrain subunit interactions. Following scaffold digestion, the MCP capsid domains form strong interactions that maintain capsid structure throughout maturation. The scaffold constraints appear critical for capsid size determination and provide important understanding of the factors governing capsid assembly in general and expands our understanding of these ecologically and biomedically important viruses.

molecular biology↗

bioRxiv2023

Insights into a viral motor: the structure of the HK97 packaging termination assembly

Double-stranded DNA viruses utilise machinery, made of terminase proteins, to package viral DNA into the capsid. For cos bacteriophage, a defined signal, recognised by small terminase, flanks each genome unit. Here we present the first structural data for a cos virus DNA packaging motor, assembled from the bacteriophage HK97 terminase proteins, procapsids encompassing the portal protein, and DNA containing a cos site. The cryo-EM structure is consistent with the packaging termination state adopted after DNA cleavage, with DNA density within the large terminase assembly ending abruptly at the portal protein entrance. Retention of the large terminase complex after cleavage of the short DNA substrate suggests that motor dissociation from the capsid requires headful pressure, in common with pac viruses. Interestingly, the clip domain of the 12-subunit portal protein does not adhere to C12 symmetry, indicating asymmetry induced by binding of the large terminase/DNA. The motor assembly is also highly asymmetric, showing a ring of 5 large terminase monomers, tilted against the portal. Variable degrees of extension between N- and C-terminal domains of individual subunits suggest a mechanism of DNA translocation driven by inter-domain contraction and relaxation.

molecular biology↗

bioRxiv2022

A structural dendrogram of the actinobacteriophage major capsid proteins provides important structural insights into the evolution of capsid stability

Many double-stranded DNA viruses, including tailed bacteriophages (phages) and herpesviruses, use the HK97-fold in their major capsid protein to make the capsomers of the icosahedral viral capsid. Following the genome packaging at near-crystalline densities, the capsid is subjected to a major expansion and stabilization step that allows it to withstand environmental stresses and internal high pressure. Several different mechanisms for stabilizing the capsid have been structurally characterized, but how these mechanisms have evolved is still not understood. Using cryo-EM structure determination, structural comparisons, phylogenetic analyses, and Alphafold predictions, we have constructed a detailed structural dendrogram describing the evolution of capsid structural stability within the actinobacteriophages. The cryo-EM reconstructions of ten capsids solved to resolutions between 2.2 and 4 [A]ngstroms revealed that eight of them exhibit major capsid proteins that are linked by a covalent cross-linking (isopeptide bond) between subunits that was first described in the HK97 phage. Those covalent interactions ultimately lead to the formation of mutually interlinked capsomers that has been compared to the structure of chain mail. However, three of the closely related phages do not exhibit such an isopeptide bond as demonstrated by both our cryo-EM maps and the lack of the required residue. This work raises questions about the importance of previously described capsid stabilization mechanisms.

biochemistry↗

bioRxiv2022

Structural basis of DNA packaging by a ring-type ATPase from an archetypal viral system

Many essential cellular processes rely on substrate rotation or translocation by a multi-subunit, ring-type NTPase. A large number of double-stranded DNA viruses, including tailed bacteriophages and herpes viruses, use a homomeric ring ATPase to processively translocate viral genomic DNA into procapsids during assembly. Our current understanding of viral DNA packaging comes from three archetypal bacteriophage systems: cos, pac and phi29. Detailed mechanistic understanding exists for pac and phi29, but not for cos. Here we reconstituted in vitro a cos packaging system based on bacteriophage HK97 and provided a detailed biochemical and structural description. We used a photobleaching-based, single-molecule assay to determine the stoichiometry of the DNA-translocating ATPase large terminase. Crystal structures of the large terminase and DNA-recruiting small terminase, a first for both this phage and a cos system, reveal unexpected mechanistic similarities between cos and pac systems. At the same time, mutational and biochemical analyses indicate a new regulatory mechanism for ATPase multimerization and coordination in the HK97 system. This work therefore establishes a framework for studying the evolutionary relationships between ATP-dependent DNA translocation machineries in double-stranded DNA viruses.

biochemistry↗

bioRxiv2021

Potent neutralizing nanobodies resist convergent circulating variants of SARS-CoV-2 by targeting novel and conserved epitopes

There is an urgent need to develop effective interventions resistant to the evolving variants of SARS-CoV-2. Nanobodies (Nbs) are stable and cost-effective agents that can be delivered by novel aerosolization route to treat SARS-CoV-2 infections efficiently. However, it remains unknown if they possess broadly neutralizing activities against the prevalent circulating strains. We found that potent neutralizing Nbs are highly resistant to the convergent variants of concern that evade a large panel of neutralizing antibodies (Abs) and significantly reduce the activities of convalescent or vaccine-elicited sera. Subsequent determination of 9 high-resolution structures involving 6 potent neutralizing Nbs by cryoelectron microscopy reveals conserved and novel epitopes on virus spike inaccessible to Abs. Systematic structural comparison of neutralizing Abs and Nbs provides critical insights into how Nbs uniquely target the spike to achieve high-affinity and broadly neutralizing activity against the evolving virus. Our study will inform the rational design of novel pan-coronavirus vaccines and therapeutics.

biophysics↗

bioRxiv2021

Probing adaptation and spontaneous firing in human auditory-nerve fibers with far-field peri-stimulus time responses

Information in sound stimuli is conveyed from sensory hair cells to the cochlear nuclei by the firing of auditory nerve fibers (ANFs). For obvious ethical reasons, single unit recordings from the cochlear nerve have never been performed in human, thus functional hallmarks of ANFs are unknown. By filtering and rectifying the electrical signal recorded at the round window of gerbil cochleae, we reconstructed a peri-stimulus time response (PSTR), with a waveform similar to the peri-stimulus time histograms (PSTHs) recorded from single ANFs. Pair-by-pair analysis of simultaneous PSTR and PSTH recordings in gerbil provided a model to predict the rapid adaptation and spontaneous discharge rates (SR) in a population of ANFs according to their location in the cochlea. We then probed the model in the mouse, in which the SR-based distribution of ANFs differs from the gerbil. We show that the PSTR-based predictions of the rapid adaptation time constant and mean SR across frequency again matched those obtained by recordings from single ANFs. Using PSTR recorded from the human cochlear nerve in 8 normal-hearing patients who underwent cerebellopontine angle surgeries for a functional cranial-nerve disorders (trigeminal neuralgia or hemifacial spasm), we predicted a rapid adaptation of about 3 milliseconds and a mean SR of 23 spikes/s in the 4 kHz frequency range in human ANFs. Together, our results support the use of PSTR as a promising diagnostic tool to map the auditory nerve in humans, thus opening new avenues to better understanding neuropathies, tinnitus, and hyperacusis.

neuroscience↗

bioRxiv2018

The apical region of the herpes simplex virus major capsid protein promotes capsid maturation

The herpesvirus capsid assembles in the nucleus as an immature procapsid precursor built around viral scaffold proteins. The event that initiates procapsid maturation is unknown, but it is dependent upon activation of the VP24 internal protease. Scaffold cleavage triggers angularization of the shell and its decoration with the VP26 and pUL25 capsid-surface proteins. In both the procapsid and mature angularized capsid, the apical region of the major capsid protein (VP5) is surface exposed. We investigated whether the VP5 apical region contributes to intracellular transport dynamics following entry into primary sensory neurons and also tested the hypothesis that conserved negatively-charged amino acids in the apical region contribute to VP26 acquisition. To our surprise neither hypothesis proved true. Instead, mutation of glutamic acid residues in the apical region delayed viral propagation and induced focal capsid accumulations in nuclei. Examination of capsid morphogenesis based on epitope unmasking, capsid composition, and ultrastructural analysis indicated that these clusters consisted of procapsids. The results demonstrate that, in addition to established events that occur inside the capsid, the exterior capsid shell promotes capsid morphogenesis and maturation.

microbiology↗