title: Structural flexibility at a major conserved antibody target on hepatitis C virus E2 antigen.
abstract: Hepatitis C virus (HCV) is a major cause of liver disease, affecting over 2% of the world's population. The HCV envelope glycoproteins E1 and E2 mediate viral entry, with E2 being the main target of neutralizing antibody responses. Structural investigations of E2 have produced templates for vaccine design, including the conserved CD81 receptor-binding site (CD81bs) that is a key target of broadly neutralizing antibodies (bNAbs). Unfortunately, immunization with recombinant E2 and E1E2 rarely elicits sufficient levels of bNAbs for protection. To understand the challenges for eliciting bNAb responses against the CD81bs, we investigated the E2 CD81bs by electron microscopy (EM), hydrogen-deuterium exchange (HDX), molecular dynamics (MD), and calorimetry. By EM, we observed that HCV1, a bNAb recognizing the N-terminal region of the CD81bs, bound a soluble E2 core construct from multiple angles of approach, suggesting components of the CD81bs are flexible. HDX of multiple E2 constructs consistently indicated the entire CD81bs was flexible relative to the rest of the E2 protein, which was further confirmed by MD simulations. However, E2 has a high melting temperature of 84.8 °C, which is more akin to proteins from thermophilic organisms. Thus, recombinant E2 is a highly stable protein overall, but with an exceptionally flexible CD81bs. Such flexibility may promote induction of nonneutralizing antibodies over bNAbs to E2 CD81bs, underscoring the necessity of rigidifying this antigenic region as a target for rational vaccine design.
authors: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037.
authors: Leopold
authors: L
authors: Kong
authors: Department of Medicine, University of California, San Diego, La Jolla, CA 92037.
authors: David E
authors: DE
authors: Lee
authors: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037.
authors: Rameshwar U
authors: RU
authors: Kadam
authors: Department of Medicine, University of California, San Diego, La Jolla, CA 92037.
authors: Tong
authors: T
authors: Liu
authors: Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA 92037.
authors: Erick
authors: E
authors: Giang
authors: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037.
authors: Travis
authors: T
authors: Nieusma
authors: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037.
authors: Fernando
authors: F
authors: Garces
authors: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037.
authors: Netanel
authors: N
authors: Tzarum
authors: Department of Medicine, University of California, San Diego, La Jolla, CA 92037.
authors: Virgil L
authors: VL
authors: Woods
authors: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037.
authors: Andrew B
authors: AB
authors: Ward
authors: Department of Medicine, University of California, San Diego, La Jolla, CA 92037.
authors: Sheng
authors: S
authors: Li
authors: Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92037; mlaw@scripps.edu wilson@scripps.edu.|The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037.
authors: Ian A
authors: IA
authors: Wilson
authors: Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA 92037; mlaw@scripps.edu wilson@scripps.edu.
authors: Mansun
authors: M
authors: Law
keywords: CD81-binding site; E2; conformational flexibility; hepatitis C virus; protein dynamics