Poxviruses are unique amongst viruses in their expression of ankyrin (ANK) repeat proteins, often found to have immunomodulatory and host range functions. Most of these viral ANK proteins contain a C-terminal domain that recruits cellular ubiquitin ligase complexes. However, several lack it or have no discernible domain, such as OPG037. Other viral ANK-only proteins are known to modulate the cellular immune response through novel interactions with host proteins, though little is known about this aspect of OPG037.

This thesis aims to characterise the expression and criticality of OPG037, determine its immunomodulatory function and investigate potential interaction partners. Previous research had identified OPG037 as anti-apoptotic, whilst this work has identified additional novel immunomodulatory functions. OPG037 inhibits multiple innate immune pathways including NF-κB and IRF signalling identified through luciferase reporter systems and measuring endogenous target genes. Quantitative proteomic analysis performed previously in the lab identified host protein DBC1 as a novel interactor of OPG037, which was confirmed in this thesis. OPG037 was found to localise to the cytosol, where it sequestered DBC1 away from the nucleus. Analysis of the biochemical mechanism found that OPG037 binds the N-terminus of DBC1, using its central ANK repeats. This interaction disrupts normal mitochondrial distribution, possibly contributing to its antiapoptotic properties. DBC1 has been well-characterised as having critical roles in the regulation of apoptosis and inflammation, and knockout cell lines generated in this work confirmed that apoptosis is suppressed in the absence of DBC1. The link between OPG037, DBC1 and the inhibition of innate immune pathways requires further investigation, though the ability to bind DBC1 and suppress NF-κB was correlated.

In conclusion, this thesis provides evidence of a novel immunomodulatory function of OPG037, and that it falls into a category of viral ANK proteins with dual anti-apoptotic and anti-inflammatory properties. Additionally, this is the first time an orthopoxviral protein has been described to interact with DBC1, highlighting its potential therapeutic value due to the role of DBC1 in cancer, metabolic disorders and neurodegenerative diseases.