A Highly Stable Prefusion Rsv F Vaccine Derived from Structural Analysis of the Fusion Mechanism

Respiratory syncytial virus (RSV) causes acute lower respiratory tract infections and is the leading cause of infant hospitalizations. Recently, a promising vaccine antigen based on the RSV fusion protein (RSV F) stabilized in the native prefusion conformation has been described. Here we report alternative strategies to arrest RSV F in the prefusion conformation based on the prevention of hinge movements in the first refolding region and the elimination of proteolytic exposure of the fusion peptide. A limited number of unique mutations are identified that stabilize the prefusion conformation of RSV F and dramatically increase expression levels. This highly stable prefusion RSV F elicits neutralizing antibodies in cotton rats and induces complete protection against viral challenge. Moreover, the structural and biochemical analysis of the prefusion variants suggests a function for p27, the excised segment that precedes the fusion peptide in the polypeptide chain

A Universal Approach to Optimize the Folding and Stability of Prefusion-Closed HIV-1 Envelope Trimers

Summary: The heavily glycosylated native-like envelope (Env) trimer of HIV-1 is expected to have low immunogenicity, whereas misfolded forms are often highly immunogenic. High-quality correctly folded Envs may therefore be critical for developing a vaccine that induces broadly neutralizing antibodies. Moreover, the high variability of Env may require immunizations with multiple Envs. Here, we report a universal strategy that provides for correctly folded Env trimers of high quality and yield through a repair-and-stabilize approach. In the repair stage, we utilized a consensus strategy that substituted rare strain-specific residues with more prevalent ones. The stabilization stage involved structure-based design and experimental assessment confirmed by crystallographic feedback. Regions important for the refolding of Env were targeted for stabilization. Notably, the α9-helix and an intersubunit β sheet proved to be critical for trimer stability. Our approach provides a means to produce prefusion-closed Env trimers from diverse HIV-1 strains, a substantial advance for vaccine development. : Rutten et al. describe a universal repair and stabilize approach that corrects rare mutations and stabilizes refolding regions to obtain high-quality HIV Envs with high yields. The crystal structure shows how the optimization of the trimer interface between α9, α6, and the intersubunit β-sheet stabilizes the membrane-proximal base. Keywords: envelope protein, chronic, ConC_base, HIV, SOSIP, stabilization, transmitted/founder, vaccine, X-ray structure, hybrid shee