Determinants of Core Shell Dependent Rotavirus Polymerase Activity
Steger, Courtney Long
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Rotaviruses (RVs) are medically significant gastrointestinal pathogens and are a leading cause of childhood mortality in many countries. The RV RNA-dependent RNA polymerase, VP1, synthesizes RNA during viral replication only in the presence of another RV protein, VP2, which comprises the innermost core shell layer of the virion. Though these VP1-VP2 interactions are essential for RV replication, the mechanism by which the core shell regulates polymerase activity remains incompletely understood. Here, we sought to identify and characterize specific regions of both VP1 and VP2 that are required for core shell dependent polymerase activity. First, we used bioinformatics approaches to analyze VP1 and VP2 sequence diversity across many RV strains and identify positional locations of critical amino acid changes within the context of known structural domains and motifs. We next tested how the identified sequence differences influenced VP2-dependent VP1 activity in vitro. These data revealed that VP1 and VP2 protein diversity correlates with functional differences between avian and mammalian RV strains. Then, we used these sequential and functional incompatibilities to map key regions of VP1 important for mediating RNA synthesis. To pinpoint critical interacting regions of VP1 and VP2, we used site directed mutagenesis to engineer several modified VP1 and VP2 proteins. Then, we employed an in vitro RNA synthesis assay to test how the introduced mutations influenced VP2-dependent VP1 activity. Altogether, our results revealed several functionally important VP1 residues critical for in vitro VP2-dependent VP1 activity, either individually or in combination with neighboring residues, including E265/L267, R614, and D971/S978/I980. Structural analyses show VP2 interactions at these surface-exposed VP1 sites, which altogether supports a direct contact model of core shell dependent RV polymerase activity. Moreover, recombinant VP1 proteins containing multiple mutations at buried residues were incapable of facilitating RNA synthesis in vitro under the assay conditions, indicating that an extensive intramolecular signaling network exists to mediate VP1 activity. Taken together, these results suggest that VP2 binding at the VP1 surface may induce intramolecular interactions critical for VP1 activity. Overall, results from these studies provide important insight into VP1-VP2 binding interface(s) that are necessary for RV replication.
General Audience Abstract
Rotaviruses (RVs) are clinically-significant gastrointestinal pathogens that cause severe diarrhea and dehydration in children. RVs encode a specialized polymerase enzyme, called VP1, which functions to synthesize RNA during viral replication. RNA synthesis activities of VP1 are tightly regulated by another RV protein, VP2, which comprises the innermost core shell layer of the virion. Though these VP1-VP2 interactions are essential for viral replication, the mechanism by which the core shell supports polymerase activity remains poorly understood. Here, we sought to identify and characterize specific regions of both VP1 and VP2 that are essential for polymerase activity in a test tube (i.e., in vitro). First, we analyzed VP1 and VP2 sequence diversity across many RV strains. Then, we tested how the identified sequence differences influenced VP2-dependent VP1 activation in vitro. To pinpoint critical regions of VP1 and VP2, we next engineered and assayed several mutant proteins. Altogether, our results revealed several functionally important residues of VP1 and VP2, which raises new ideas about VP1-VP2 binding interface(s) that are important for viral replication. Moreover, results from these studies may provide a scientific platform for the rational design of next-generation RV vaccines or antiviral therapeutics.
- Doctoral Dissertations