Structure‐function relationships in coronavirus and norovirus polymerases explored through the structure and activity of chimeric enzymes

Abstract

The COVID‐19 pandemic caused by the severe acute respiratory syndrome coronavirus‐2 (SARS CoV‐2) has spurred an unprecedented response from the scientific community to contribute timely solutions to help manage an urgent public health emergency. The RNA‐dependent RNA polymerase (RdRP) plays a critical function in replicating the genome of all RNA viruses and is one of the most intensively studied viral enzyme targets for the development of direct‐acting antiviral therapeutics. Comparisons of recently determined cryo‐EM structures of the SARS CoV‐2 RdRP with crystal structures of calicivirus, picornavirus and flavivirus RdRP's in complex with RNA and nucleoside analogue inhibitors suggest how differences in the sequences and structures of these RdRPs may result in differences in the activity of the enzyme as well as its sensitivity to different inhibitors. Molecular modeling, crystallographic studies and in vitro primer extension assays reveal how chimeric RdRPs bearing different sequence features from the RdRPs of SARS CoV‐2 and human norovirus GII.4 may contribute to differences in polymerase activity and the effects of nucleoside analogue inhibitors. These results suggest how some of the structural features of viral RdRPs may be productively targeted for the design of novel and more potent inhibitors to serve as lead compounds for the development of more effective antiviral therapeutics in the future.