Cryo-EM structure of the nucleocapsid-like assembly of respiratory syncytial virus

Respiratory syncytial virus(RSV)is a nonsegmented,negative strand RNA virus that has caused severe lower respiratory tract infections of high mortality rates in infants and the elderly,yet no effective vaccine or antiviral therapy is available.The RSV genome encodes the nucleoprotein(N)that forms helical assembly to encapsulate and protect the RNA genome from degradation,and to serve as a template for transcription and replication.Previous crystal structure revealed a decameric ring architecture of N in complex with the cellular RNA(N-RNA)of 70 nucleotides(70-nt),whereas cryo-ET reconstruction revealed a low-resolution left-handed filament,in which the crystal monomer structure was docked with the helical symmetry applied to simulate a nucleocapsid-like assembly of RSV.However,the molecular details of RSV nucleocapsid assembly remain unknown,which continue to limit our complete understanding of the critical interactions involved in the nucleocapsid and antiviral development that may target this essential process during the viral life cycle.Here we resolve the near-atomic cryo-EM structure of RSV N-RNA that represents roughly one turn of the helical assembly that unveils critical interaction interfaces of RSV nucleocapsid and may facilitate development of RSV antiviral therapy.

Histones released by NETosis enhance the infectivity of SARS-CoV-2 by bridging the spike protein subunit 2 and sialic acid on host cells

Neutrophil extracellular traps(NETs)can capture and kill viruses,such as influenza viruses,human immunodeficiency virus(HIV),and respiratory syncytial virus(RSV),thus contributing to host defense.Contrary to our expectation,we show here that the histones released by NETosis enhance the infectivity of SARS-CoV-2,as found by using live SARS-CoV-2 and two pseudovirus systems as well as a mouse model.The histone H3 or H4 selectively binds to subunit 2 of the spike(S)protein,as shown by a biochemical binding assay,surface plasmon resonance and binding energy calculation as well as the construction of a mutant S protein by replacing four acidic amino acids.Sialic acid on the host cell surface is the key molecule to which histones bridge subunit 2 of the S protein.Moreover,histones enhance cell-cell fusion.Finally,treatment with an inhibitor of NETosis,histone H3 or H4,or sialic acid notably affected the levels of sgRNA copies and the number of apoptotic cells in a mouse model.These findings suggest that SARS-CoV-2 could hijack histones from neutrophil NETosis to promote its host cell attachment and entry process and may be important in exploring pathogenesis and possible strategies to develop new effective therapies for COVID-19.