The role of surface basic amino acids of dengue virus NS 3 helicase in viral RNA replication and enzyme activities

Structure‐based mutagenesis analysis on selected conserved surface basic residues of DENV NS 3 helicase was performed using a selectable replicon and recombinant protein. We found a requirement for basic side chains of NS 3 residues #225, #268, and #538 to activate viral RNA replication and ensure RNA ‐stimulated ATP ase activity, and a critical role for R560 and R599 residues in maintaining NS 3 helicase structure, linked to its biological function and catalytic activity. Three screened NS3 second‐site mutations for R225A and R268A/E mutations elevated the functional RNA binding of NS 3 helicase and compensated the replication defect of the original NS 3 mutant replicons.