Functions of Norovirus VP1: A Multi-Faceted Capsid Protein

Human noroviruses, commonly known as "winter vomiting disease" are a major cause of gastroenteritis worldwide for which there is no treatment or preventative strategies available. Outbreaks of norovirus often occur in partly enclosed communities, most notably hospital wards and care homes where closes and restrictions apply a drain on healthcare services. In the UK alone every year, norovirus outbreaks result in the loss of over 15,000 bed days and a financial burden of over £100 million. Norovirus infection is estimated to result in the loss of over 200,000 lives each year, primarily in the most vulnerable populations such as found in lower and middle income countries (LIMC), the young and elderly and those with a compromised immune system.
The disease-causing viruses are small, each one consisting of the viral genome enclosed within a protein capsid comprised mostly of the major viral structural protein VP1. This is a key protein in virus replication. It is responsible for the delivery of the virus genome to start an infection and production of more virus to spread infection both between cells and between people. Importantly, as the major constituent of viral capsids, VP1 is important for generating an anti-viral immune response and is the first viral component the immune system experiences during when a person become infected. This research will study how VP1 functions at different steps of the virus life-cycle to start infection and spread infection to new cells. Understanding these fundamental processes will aid the development of future approaches to disease control.

As positive-sense RNA viruses, noroviruses possess small genomes that produce a limited set of proteins. To compensate for this limitation they have evolved proteins that have manifold functions during the virus life-cycle and increase their "genetic economy". The norovirus structural protein VP1 is an example of a multi-functional protein. It is the major component of viral capsids and must be robust to protect the vulnerable viral genome. It is essential for receptor binding and allowing controlled virion disassembly to deliver the viral genome during endocytosis. Inside infected cells it is involved in regulating viral genome synthesis and is essential for assembly of new infectious virions. As part of my recent work, resources are now in place to understand how VP1 fulfils two essential roles.
Using inactivation of infectious virus with structural and molecular biology I have identified a viral particle that has a novel VP1 conformation. I hypothesise that this conformation of VP1 in the capsid is involved in delivery of the viral genome. Using biochemical assays with imaging and structural techniques I will discover how VP1 directs delivery of the viral genome during endocytosis and the factors involved in this process. In contrast to the disassembly of the capsid that must take place during endocytosis, production of nascent virions requires the controlled assembly of VP1 with the viral genome. I have demonstrated that VP1 localises with membrane-associated non-structural proteins believed to be involved in viral RNA replication. I hypothesise that the interaction between VP1 and these viral non-structural proteins is part of a regulated complex required for virion assembly. With my experience studying macromolecular complexes, I will investigate how VP1 interacts with viral factors to assemble virions. By understanding how VP1 functions to regulate entry into the cells and production of virions, improved vaccine and anti-viral approaches can be created.

As a fundamental research project, the academic community will be the major beneficiaries of this work as outlined in the Academic Beneficiaries section. Within the duration of this fellowship the main non-academic beneficiaries for the proposed research are the UK and global economies. This is through my professional development and transition to an independent researcher career and the training of junior researchers (e.g. the PDRA, tba) as highly skilled professionals. This research will also strengthen the economic competitiveness of the UK by growing world-recognised life-science research (e.g. virology). Other beneficiaries include the general public, through increased understanding and communication of scientific principles (e.g. infection control), healthcare organisations where norovirus is a major burden (e.g. hospital wards) and government organisation in countries where gastroenteritis is a cause of significant morbidity and mortality. Beyond the duration of this fellowship, healthcare organisations and the general public will continue to be major non-academic beneficiaries through the potential development of novel norovirus disease control strategies (e.g. vaccine or anti-viral development). This will increase quality of life, particularly for vulnerable populations (e.g. the elderly and immunocompromised) and relieve healthcare cost-associated burdens. This will require further investigations, likely requiring new academic and industrial partners (e.g. for vaccine manufacture), who will be future beneficiaries.