Increased Capsid Oligomerization Is Deleterious To Dengue Virus Particle Production

The capsid protein (C) of dengue virus is required for viral infectivity as it packages viral RNA genome into infectious particles. C exists as a homodimer that forms via hydrophobic interactions between the alpha 2 and alpha 4 helices of monomers. To identify C region(s) important for virus particle production, a complementation system was employed in which single-round infectious particles are generated by trans-encapsidation of a viral C-deleted genome by recombinant C expressed in mosquito cells. Mutants harbouring a complete alpha 3 deletion, or a dual Ile65-/Trp69-to-Ala substitution in the alpha 3 helix, exhibited reduced production of infectious virus. Unexpectedly, higher proportions of oligomeric C were detected in cells expressing both mutated forms as compared with the wild-type counterpart, indicating that the alpha 3 helix, through its internal hydrophobic residues, may down-modulate oligomerization of C during particle formation. Compared with wild-type C, the double Ile65-/Trp69 to Ala mutations appeared to hamper viral infectivity but not C and genomic RNA incorporation into the pseudo-infectious virus particles, suggesting that increased C oligomerization may impair DENV replication at the cell entry step.