MECHANISTIC INSIGHTS INTO THE STRUCTURE AND FUNCTION OF THE HEPATITIS E VIRUS OPEN READING FRAME 1 PROTEIN

Abstract

Hepatitis E virus (HEV) is a positive sense single-stranded RNA virus in the Hepeviridae family that is responsible for over 3.3 million infections and approximately 66,000 deaths per annum. Pregnant women represent a particularly vulnerable population, suffering up to 30% mortality in the third trimester and near 3,000 stillbirths every year. Currently, there are no direct acting antivirals (DAAs) against HEV, nor are there non-teratogenic treatments available, necessitating a further understanding of the viral replication cycle and the identification of novel therapeutic targets. There is a vaccine against HEV available but is only licensed in China. HEV encodes three open reading frames: the open reading frame (ORF)1 polyprotein encompassing the viral replicase, the ORF2 capsid, and the ORF3 viroporin necessary for viral egress. ORF1, the largest of these three viral proteins is essential for genome replication, though it is currently unknown how the different domains function within a defined structural context, and what role it plays in host innate immunity antagonism, if any. The work outlined in this thesis advance the field’s knowledge in the following ways: (i) the identification of a metal coordinating structural domain (MCSD) and novel upstream interdomain interaction necessary for viral replication utilizing a combined computational, genetic, and biochemical approach, yielding a structural model of the ORF1 polyprotein (Chapter II), and (ii) the identification and partial characterization of HEV ORF1’s ability to antagonize the cGAS/STING innate immunity pathway in a proteasome dependent manner (Chapter III). These findings, in addition to the other important recent advances in the HEV field constitute a foundation for the development of novel DAAs and immunotherapeutics to combat this dreadful disease.