Discrete conformations of epitope II on the hepatitis C virus E2 protein for antibody-mediated neutralization and nonneutralization

Abstract

The X-ray crystal structure of epitope II on the E2 protein of hepatitis C virus, in complex with nonneutralizing antibody mAb#12, has been solved at 2.90-Å resolution. The spatial arrangement of the essential components of epitope II (ie, the C-terminal α-helix and the N-terminal loop) was found to deviate significantly from that observed in those corresponding complexes with neutralizing antibodies. The distinct conformations are mediated largely by the flexibility of a highly conserved glycine residue that connects these components. Thus, it is the particular tertiary structure of epitope II, which is presented in a spatial and temporal manner, that determines the specificity of antibody recognition and, consequently, the outcome of neutralization or nonneutralization.H epatitis C is a major public health problem worldwide. More than 170 million people are infected by the hepatitis C virus (HCV) (1). Approximately 70% of infected people fail to clear the virus during the acute phase of the disease and become chronic carriers (2). Liver cirrhosis, which develops in about 10-20% of chronically infected patients, is linked with a high risk for hepatocellular carcinoma in later life (2, 3). To date, there is neither an effective immune globulin for prophylaxis nor a vaccine for the prevention of hepatitis C. The development of a safe and effective HCV vaccine remains a top priority for the global control of HCV infections.The HCV envelope glycoprotein E2 has long been considered an important immunogenic target in efforts to develop an HCV vaccine candidate. This consideration is largely based on the role of the E2 protein in facilitating the entry of HCV into hepatocytes via interaction with the host entry factors (4-10). Recently, the crystal structure of the E2 core, in complex with a neutralizing antibody, was solved (11). The E2 core study described the interface crucial for host entry factor CD81-mediated entry, thus providing a site of vulnerability that can be exploited in immunogen design. The crystal structure also revealed that nearly 62% of the E2 core amino acid residues are either disordered or in loop structures, the overall effect of which indicates a striking flexibility in the E2 protein structures. Whether the intrinsic structural heterogeneity of the E2 protein is linked to the viral entry process or not is currently unknown.Epitope II resides on the E2 protein between residues 427 and 446, a location that places it in the vicinity of the described E2-CD81 interface in the flexible area of the E2 protein (11-13). Paradoxically, different antibodies are able to bind to a similar set of residues on epitope II; however, their interactions with these residues can lead to either HCV neutralization or nonneutralization, as defined in an in vitro HCV cell culture system (12, 13). In addition, some epitope II-specific nonneutralizing antibodies were shown to interfere with the neutralization by antibodies at epitope I, another epitope on the E2 protein between residues 412 and 426 (12). Furthermore, de...

Structural Basis for Penetration of the Glycan Shield of Hepatitis C Virus E2 Glycoprotein by a Broadly Neutralizing Human Antibody

“…Our results and those of others (50,51,58) suggest that HCV may also employ structural flexibility as an immune evasion strategy. The crystal structure of the HCV E2 core revealed that ϳ60% of all residues are either disordered or in loops, implying considerable overall flexibility (51).…”

“…The crystal structure of the HCV E2 core revealed that ϳ60% of all residues are either disordered or in loops, implying considerable overall flexibility (51). Neutralizing and non-neutralizing mouse mAbs specific for an E2 epitope comprising residues 427-446 were found to bind distinct conformations of this epitope that determined recognition specificity (58). Here we have shown that the E2 412-423 epitope can adopt at least three different conformations, which may contribute to reducing its immunogenicity in HCV-infected individuals (14).…”

Structural flexibility at a major conserved antibody target on hepatitis C virus E2 antigen

“…When superposed on the E2c-AR3C crystal structure, bNAb HC84-27 does not clash with the E2 protein and binds at an angle of approach comparable to bNAb AR3C, the antibody present in the E2c crystal structure. However, mAb 8 would severely clash with E2 if superposed on the E2c structure in the same manner because its epitope is buried by the E2 β-sandwich (24,42). The ability of mAb 8 to neutralize some viruses, albeit weakly, suggests that major conformational rearrangements at AS434 are possible that would allow mAb 8 to bind without a clash.…”

In silico Epitope Mapping of Glucose-6-Phosphate Isomerase: A Rheumatoid Arthritis Autoantigen

“…For example, biological activity of human CD20 monoclonal antibodies is linked to the unique epitopes on CD20 [71]. It has also been demonstrated that spatial arrangements of the secondary structural elements in epitope II on the hepatitis C virus E2 protein can determine how its specific antibody binds and ultimately directs the outcomes of either antibodymediated neutralization or non-neutralization [59]. The murine GPI antigen dimer structure extends from left to right by ~8.0 nm and from top to bottom by ~7.8 nm.…”

“…All the murine GPI-46H9 complexes and all the human GPI-46H9 complexes showed the 11H3 Fv component for all the 10 epitope models, each attached to one and the same surface region around the predicted epitope model (marked in red in Figure 1). Details of the predicted epitope-paratope interactions such as hydrogen bonding, salt bridges, ionic, cation-π, and hydrophobic [59][60][61] interactions have been summarized (Supplemental Tables 7-22). …”