Structural insights into the transcription and translation of murine norovirus RNA

Abstract

Noroviruses are positive-sense single-stranded RNA viruses which, in humans, cause rapid onset diarrhoea and vomiting. There is an estimated 21 million cases of noroviral gastroenteritis in the United States per year. The work in this thesis has focused on two noroviral proteins, the viral protein genome-linked (VPg), and the viral RNA dependent RNA polymerase (NS7pol). The VPg protein is covalently linked to the 5' end of the noroviral genome and is a key component of translation and replication initiation in noroviruses. Using Nuclear magnetic resonance spectroscopy (NMR) we have analysed the murine norovirus (MNV) and a human norovirus VPg (Lordsdale virus (LDV)) proteins. The VPg protein of both viruses has a small structured helical core with extensive N and C-terminal flexible regions. We has also determined the structure of the MNV NS7pol as well as two high fidelity mutants (P72S and E75S) using X-ray crystallography. The NS7pol protein has a very similar “right drinking hand” structure to other RNA dependent RNA polymerases. The fidelity mutants were structurally identical to the wild type protein but had subtle changes in local hydrogen bonding networks. This is consistent with similar studies performed with picornaviral polymerases. In addition we used NMR and surface plasmon resonance to characterise the interaction of the MNV VPg protein with the NS7pol protein. The interaction between full length VPg and MNV NS7pol is weak, (KD ~160 μM). In addition the NS7pol interacts with both the full length VPg and the core domain of this protein.