Biology subjects

Calcraft, T.

Publications and source records attributed to Calcraft, T..

3 recordsLinked to original sources

bioRxiv2025

Topological defects drive influenza glycoprotein lattice assembly on spherical membranes

Lipid-enveloped viruses, such as influenza virus, assemble by budding from infected cell membranes, packaging internal components including the genome and acquiring an envelope containing surface glycoproteins in the process. Influenza C virus possesses a single surface glycoprotein, the haemagglutinin-esterase-fusion (HEF) protein that forms hexagonal arrays1,2 on the membrane envelope and is sufficient for budding of spherical particles3. However, a two-dimensional hexagonal lattice cannot completely cover a spherical virus membrane without defects. Using electron cryotomography (cryo-ET), we study the structural arrangement of the influenza C virus surface and find the hexagonal HEF lattice contains 5-fold and 7-fold defects organised in grain boundaries. The number of excess dislocations increases with system size while maintaining a net topological charge near 12. Our observations of defects in spherical crystals on influenza C virus particles of varying radius and shape matches theoretical predictions of continuum elastic theory4 for the proliferation of defects on soft lattices and experimental observations5 on colloidal systems. These findings provide new principles for assembly of pleomorphic viruses, extending the description of defects required for viral lattice assembly beyond the Caspar-Klug theory6 developed for isometric viruses. Our study informs a wide range of molecular self-assembly processes in biology and may also have implications for developing lattice materials with curved surfaces.

biophysics↗

bioRxiv2025

In situ cryo-electron tomography of vaccinia virus exit from infected cells

Poxvirus-infected cells release newly assembled virions via Golgi-mediated envelopment and subsequent exocytosis at the plasma membrane, prior to cell lysis. Here, we used cryo-electron tomography and structured illumination microscopy to study vaccinia egress. Our 3D analysis reveals that Golgi-mediated envelopment is a flexible process that involves remodelling of the enfolding membrane and a final step that seals a small pore. During subsequent exocytosis, the viral outer membrane fuses with the plasma membrane but retains a distinct identity, beneath which septins and clathrin are independently recruited. Clathrin enhances actin-dependent viral spread, while septins suppress virus release from the cell. We found that septin filaments run parallel to the inner surface of the plasma membrane beneath virions attached to the cell surface. In contrast, clathrin induces the formation of plasma membrane invaginations in distinct subdomains. We propose that actin assembly at these subdomains provides a template for subsequent virus-induced actin polymerization.

cell biology↗

bioRxiv2022

Cryo-ET of infected cells reveals that a succession of two lattices drives vaccinia virus assembly

During its cytoplasmic replication, vaccinia virus assembles non-infectious spherical immature virions (IV) coated by a viral D13 lattice. Subsequently, IV mature into infectious brick-shaped intracellular mature virus (IMV) that lack D13. Here, we performed cryo-electron tomography of frozen-hydrated vaccinia-infected cells to structurally characterise the maturation process in situ. During IMV formation a new viral core forms inside IV with a wall consisting of trimeric pillars arranged in a new pseudohexagonal lattice. This lattice appears as a palisade in cross-section. During maturation, which involves a 50% reduction in virion volume, the viral membrane becomes corrugated as it adapts to the newly formed viral core in a process that does not appear to require membrane removal. Our study suggests that the length of this core is determined by the D13 lattice and that the consecutive D13 and palisade lattices control virion shape and dimensions during vaccinia assembly and maturation.

microbiology↗