An effective vaccine to the antigenically diverse hepatitis C virus (HCV) must target conserved immune epitopes. Here, we investigate cross-neutralization of HCV genotypes by broadly neutralizing antibodies (bNAbs) encoded by the relatively abundant human gene family V H 1-69. We have deciphered the molecular requirements for cross-neutralization by this unique class of human antibodies from crystal structures of HCV E2 in complex with bNAbs. An unusually high binding affinity is found for germ line–reverted versions of V H 1-69 precursor antibodies, and neutralization breadth is acquired during affinity maturation. Deep sequencing analysis of an HCV-immune B cell repertoire further demonstrates the importance of the V H 1-69 gene family in the generation of HCV bNAbs. This study therefore provides critical insights into immune recognition of HCV with important implications for rational vaccine design.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

Structure of Hepatitis C virus envelope glycoprotein E1 antigenic site 314–324 in complex with antibody IGH526

Hepatitis C virus (HCV) is a positive-strand RNA virus within the Flaviviridae family. The viral “spike” of HCV is formed by two envelope glycoproteins, E1 and E2, which together mediate viral entry by engaging host receptors and undergoing conformational changes to facilitate membrane fusion. While E2 can be readily produced in the absence of E1, E1 cannot be expressed without E2 and few reagents, including monoclonal antibodies, are available for study of this essential HCV glycoprotein. A human MAb to E1, IGH526, was previously reported to cross-neutralize different HCV isolates and, therefore, we sought to further characterize the IGH526 neutralizing epitope to obtain information for vaccine design. Here, we found that MAb IGH526 bound to a discontinuous epitope, but with a major component corresponding to E1 residues 314-324. The crystal structure of IGH526 Fab with this E1 glycopeptide at 1.75Å resolution revealed that the antibody binds to one face of an α-helical peptide. Single mutations on the helix substantially lowered IGH526 binding but did not affect neutralization, indicating either that multiple mutations are required or that additional regions are recognized by the antibody in the context of the membrane-associated envelope oligomer. Finally, molecular dynamics simulations indicate the free peptide is flexible in solution, suggesting that it requires stabilization for use as a candidate vaccine immunogen.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2014

Structure of Hepatitis C Virus Envelope Glycoprotein E2 Antigenic Site 412-423 in Complex with Antibody AP33

Abstract Not Provided

CHEM↗

DOE OSTI2014

Hepatitis C Virus E2 Envelope Glycoprotein Core Structure

Hepatitis C virus (HCV), a Hepacivirus, is a major cause of viral hepatitis, liver cirrhosis, and hepatocellular carcinoma. HCV envelope glycoproteins E1 and E2 mediate fusion and entry into host cells and are the primary targets of the humoral immune response. The crystal structure of the E2 core bound to broadly neutralizing antibody AR3C at 2.65 angstroms reveals a compact architecture composed of a central immunoglobulin-fold β sandwich flanked by two additional protein layers. The CD81 receptor binding site was identified by electron microscopy and site-directed mutagenesis and overlaps with the AR3C epitope. The x-ray and electron microscopy E2 structures differ markedly from predictions of an extended, three-domain, class II fusion protein fold and therefore provide valuable information for HCV drug and vaccine design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗