Dengue virus 2 capsid protein chaperones strand displacement without altering the capsid-coding region hairpin element's structural functionality

By virtue of its chaperone activity, the capsid protein of dengue virus strain 2 (DENV2C) promotes nucleic acid structural rearrangements. However, the role of DENV2C during the interaction of RNA elements involved in stabilizing the 59-39 panhandle structure of DENV RNA is still unclear. Therefore, we determined how DENV2C affects structural functionality of the capsid-coding region hairpin element (cHP) during RNA rearrangement of the 9-nt conserved sequence (5CS) to its complementary 3CS counterpart. The cHP element has two distinct functions: a role in translation start codon selection and a role in RNA synthesis. Our results showed that the cHP hairpin impedes annealing between the 5CS and the 3CS elements. Although DENV2C does not modulate structural functionality of the cHP hairpin, it accelerates annealing and specifically promotes strand displacement of 3CS during 59-39 panhandle formation. Furthermore, DENV2C exerts its chaperone activity by favoring one of the active conformations of the cHP element. Based on our results, we propose mechanisms for annealing and strand displacement involving the cHP element. Thus, our results provide mechanistic insights on how DENV2C regulates RNA synthesis by modulating essential RNA elements in the capsid-coding region, that in turn allow for DENV replication.