Structural basis for human respiratory syncytial virus NS1-mediated modulation of host responses

Abstract

Human respiratory syncytial virus (hRSV) is a major cause of morbidity and mortality in the pediatric, elderly, and immune compromised populations1,2. A gap in our understanding of hRSV disease pathology is the interplay between virally encoded immune antagonists and host components that limit hRSV replication. hRSV encodes for non-structural (NS) proteins that are important immune antagonists3–6; however, the role of these proteins in viral pathogenesis is incompletely understood. Here we report the crystal structure of hRSV NS1 protein, which suggests that NS1 is a structural paralog of hRSV matrix (M) protein. Comparative analysis of the shared structural fold with M revealed regions unique to NS1. Studies on NS1 WT or mutant alone or in recombinant RSVs demonstrate that structural regions unique to NS1 contribute to modulation of host responses, including inhibition of type I IFN responses, suppression of dendritic cell maturation, and promotion of inflammatory responses. Transcriptional profiles of A549 cells infected with recombinant RSVs show significant differences in multiple host pathways, suggesting that NS1 may have a greater role in regulating host responses than previously appreciated. These results provide a framework to target NS1 for therapeutic development to limit hRSV associated morbidity and mortality.

The nonstructural proteins of Pneumoviruses are remarkably distinct in substrate diversity and specificity

“…As mentioned, there is very limited conservation of key residues, such as T36, in the NS2 proteins of the two viruses, whose significance is unknown [ 32 ]. Recently determined crystal structure of RSV NS1 showed some similarity of structural fold with the RSV M protein [ 28 ]. The significance of this exclusive similarity at the higher structural level is also enigmatic since the M protein is a virion structural protein that links the genome RNA nucleocapsid to the viral envelope, with no known role in IFN suppression.…”

“…Intriguingly, the primary structures of the NS proteins show no similarity with any other protein in biology; thus, bioinformatic analysis of their sequences offers no clue to their evolutionary origin or functional domains [ 6 , 9 , 24 ]. Except for the recently solved crystal structure of RSV NS1 [ 28 ], the higher order structure of the pneumoviral NS proteins has also remained unknown, in part due to difficulties of expression of the recombinant proteins; moreover, the crystal structure of RSV NS1 [ 28 ] did not offer any mechanistic insight into its IFN-suppressive function. Nonetheless, we have recently shown that the PVM NS proteins specifically degrade several mouse ISGs, namely IFITM1, TRAFD1 and ISG20 [ 24 ].…”

Role of Type I Interferon (IFN) in the Respiratory Syncytial Virus (RSV) Immune Response and Disease Severity

“…NS1 and NS2 have been postulated to have various roles in RSV pathogenesis, generally linked to their anti-IFN activity. In addition to antagonizing type I IFN, NS1, and NS2 may negatively modulate dendritic cell maturation, affect Th17 lymphocyte proliferation, and promote Th2 polarization (35, 98–105). Deletion of anti-IFN proteins NS1 and NS2 in RSV live vaccines is responsible for attenuated phenotypes (89).…”

Conformational Isomerization Involving Conserved Proline Residues Modulates Oligomerization of the NS1 Interferon Response Inhibitor from the Syncytial Respiratory Virus

“…In this work, we uncover insoluble aggregation pathway (NS1Agg) that takes place at salt. This explains the apparent contradiction observed in the lack of effect of residues F17, F56, Y125 in which structure clearly links them to the stabilization of the C-terminal helix, since the thermal denaturation reported therein is in fact insoluble aggregation 12 .…”

“…reported by its single and highly sensitive Trp90, preceding the global unfolding transition corresponding to the main ß-sheet core 12 . Although there is no specific protein target defined in therms of binding affinity or structure, this mobile C-terminal helix might have important implications in structure 33 .…”