Comprehensive overview of the multifaceted roles of non-structural proteins of Orthoflavivirus in replication and immunopathology.

The genus Orthoflavivirus, encompassing formidable global pathogens such as Dengue (DENV), Zika (ZIKV), and West Nile (WNV) viruses, utilizes a compact positive-sense RNA genome to encode a sophisticated arsenal of seven non-structural (NS) proteins that dictate the outcome of the host-pathogen standoff. These proteins-NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5-function as a multifunctional molecular consortium, where the enzymatic dominance of the NS3 protease/helicase and NS5 polymerase/methyltransferase drives viral proteolysis and genomic synthesis. Simultaneously, the hydrophobic scaffolds of NS2A, NS4A, and NS4B orchestrate the biogenesis of endoplasmic reticulum-derived replication organelles, providing a privileged microenvironment that shields viral RNA from cellular sensors. Beyond replication, these proteins serve as the frontline of immune evasion; the secreted lipoprotein NS1 acts as a potent virulence factor by triggering "cytokine storms" and vascular permeability, while NS5 and the NS4 complex potently suppress Type I Interferon (IFN) signalling by intercepting the RIG-I/MDA5-MAVS axis and inducing the degradation of STAT transducers. Given the rapid expansion of mosquito vectors and the persistent absence of broad-spectrum antivirals, reviewing the structural biology and interactomes of these NS proteins is a critical priority for global biosecurity. By synthesising the current understanding of these "molecular architects," this review highlights how targeting the conserved interfaces of the replication complex can bridge the "therapeutic gap," offering a pathway toward universal countermeasures against current and emerging threats.