Biology subjects

Bhella, D.

Publications and source records attributed to Bhella, D..

4 recordsLinked to original sources

bioRxiv2018

Calicivirus VP2 forms a portal to mediate endosome escape

To initiate the infectious process, many viruses enter their host cells by triggering endocytosis following receptor engagement. The mechanism by which non-enveloped viruses, such as the caliciviruses, escape the endosome is however poorly understood. The Caliciviridae include many important human and animal pathogens, most notably norovirus, the cause of winter vomiting disease. Here we show that VP2, a minor capsid protein encoded by all caliciviruses, forms a large portal assembly at a unique three-fold symmetry axis following receptor engagement. This feature surrounds an open pore in the capsid shell. We hypothesise that the VP2 portal complex is the means by which the virus escapes the endosome, pene-trating the endosomal membrane to release the viral genome into the cytoplasm. Cryogenic electron microscopy (cryoEM) and asymmetric reconstruction were used to investigate structural changes in the capsid of feline calicivirus (FCV) that occur when the virus binds to its cellular receptor junctional adhesion molecule-A (fJAM-A). Near atomic-resolution structures were calculated for the native virion alone and decorated with soluble receptor fragments. We present atomic models of the major capsid protein VP1 in the presence and absence of fJAM-A, revealing the contact interface and conformational changes brought about by the interaction. Furthermore, we have calculated an atomic model of the portal protein VP2 and revealed the structural changes in VP1 that lead to pore formation. While VP2 was known to be critical for the production of infectious virus, its function has been hitherto undetermined. Our finding that VP2 assembles a portal that is likely responsible for endosome escape represents a major step forward in our understanding of both the Caliciviridae and icosahedral RNA containing viruses in general.

microbiology↗

bioRxiv2018

Structure of the Macrobrachium rosenbergii Nodavirus: A new genus within the Nodaviridae?

Macrobrachium rosenbergii nodavirus (MrNV) is a pathogen of freshwater prawns that poses a threat to food-security and causes significant economic losses in the aquaculture industries of many developing nations. A detailed understanding of the MrNV virion structure will inform the development of strategies to control outbreaks. The MrNV capsid has also been engineered to display heterologous antigens, thus knowledge of its atomic resolution structure will benefit efforts to develop tools based on this platform. Here we present an atomic-resolution model of the MrNV capsid protein, calculated by cryogenic electron microscopy (cryoEM) of MrNV virus-like particles (VLPs) produced in insect cells, and three-dimensional image reconstruction at 3.3 [A] resolution. CryoEM of MrNV virions purified from infected freshwater prawn post-larvae yielded a 6.6 [A] resolution structure confirming the biological relevance of the VLP structure.\n\nOur data revealed that unlike other known nodaviruses structures, which have been shown to assemble capsids having trimeric spikes, MrNV assembles a T=3 capsid with dimeric spikes. We also found a number of surprising similarities between the MrNV capsid structure and that of the Tombusviridae. 1. An extensive network of N-terminal arms lines the capsid interior forming long-range interactions to lace together asymmetric units. 2. The capsid shell is stabilised by three pairs of Ca2+ ions in each asymmetric unit. 3. The protruding spike domain exhibits a very similar fold to that seen in the spikes of the tombusviruses. These structural similarities raise questions concerning the correct taxonomic classification of MrNV.

microbiology↗

bioRxiv2018

Structure of the herpes-simplex virus portal-vertex

Herpesviruses include many important human pathogens such as herpes simplex virus, cytomegalovirus, varicella-zoster virus and the oncogenic Epstein-Barr virus and Kaposi-sarcoma associated herpesvirus. Herpes virions contains large icosahedral capsids that have a portal at a unique five-fold vertex, similar to that seen in the tailed bacteriophages. The portal is a molecular motor through which the viral genome enters the capsid during virion morphogenesis. The genome also exits the capsid through the portal-vertex when it is injected through the nuclear-pore into the nucleus of a new host cell to initiate infection. Structural investigations of the herpesvirus portal-vertex have proven challenging, owing to the small size of the tail-like portal-vertex associated tegument (PVAT), and the dense tegument layer that lays between the nucleocapsid and the viral envelope, obscuring the view of the portal-vertex. Here we show the structure of the herpes simplex virus portal-vertex at sub-nanometer resolution, solved by electron cryomicroscopy (cryoEM) and single-particle 3D reconstruction. This led to a number of new discoveries including the presence of two previously unknown portal associated structures that occupy the sites normally taken by the penton and the Ta triplex. Our data revealed that the PVAT is composed of ten copies of the C-terminal domain of pUL25, which are uniquely arranged as two tiers of star-shaped density. Our 3D reconstruction of the portal-vertex also shows that one end of the viral genome extends outside the portal in the manner described for some bacteriophage but not previously seen in any eukaryote viruses. Finally, we show that the viral genome is consistently packed in a highly-ordered left-handed spool to form concentric shells of DNA. Our data provide new insights into the structure of a molecular machine critical to the biology of an important class of human pathogens.

microbiology↗

bioRxiv2017

Cryo-Electron Microscopy Structure of the Macrobrachium Rosenbergii Nodavirus Capsid at 7 Angstroms Resolution

White tail disease in the giant freshwater prawn Macrobrachium rosenbergii causes significant economic losses in shrimp farms and hatcheries and poses a threat to food-security in many developing countries. Outbreaks of Macrobrachium rosenbergii nodavirus (MrNV), the causative agent of white tail disease (WTD) are associated with up to 100% mortality rates. Recombinant expression of the capsid protein of MrNV in insect cells leads to the production of VLPs closely resembling the native virus. We have investigated the structure of MrNV VLPs by cryogenic electron microscopy, determining a structure of the viral capsid at 7 angstroms resolution. Our data show that MrNV VLPs package nucleic acids in a manner reminiscent of other known nodavirus structures. The structure of the capsid however shows striking differences from insect and fish infecting nodaviruses, which have been shown to assemble trimer-clustered T=3 icosahedral virus particles. MrNV particles have pronounced dimeric blade-shaped spikes extending up to 6 nm from the outer surface of the capsid shell. Our structural analysis supports the assertion that MrNV along with the related virus of marine shrimp Penaeus vannamei nodavirus (PvNV) may represent a new genus of the Nodaviridae.\n\nAuthor summaryMacrobrachium rosenbergii nodavirus (MrNV) is the causative agent of white tail disease (WTD) which leads to 100% mortality in shrimp-farms growing giant freshwater prawn (M. rosenbergii). MrNV is therefore a significant threat to food security and causes severe economic losses in developing countries such as Malaysia, Indonesia, Pakistan, Thailand and India. Here we have used electron microscopy to study the three-dimensional structure of MrNV, revealing that the viral capsid - the protein shell that encloses the viral genome, protecting it and transporting it from one host to the next - is differently organised to capsids produced by other viruses in the nodavirus family. The virus was found to have large blade-like spikes on its outer surface that are likely important in the early stages of infection, when the virus attaches to and enters a host cell.

microbiology↗