Recognition of a highly conserved glycoprotein B epitope by a bivalent antibody neutralizing HCMV at a post-attachment step

• Published in: PLoS pathogens Vol. 16; no. 8; p. e1008736
• Main Authors: Ye, Xiaohua, Su, Hang, Wrapp, Daniel, Freed, Daniel C., Li, Fengsheng, Yuan, Zihao, Tang, Aimin, Li, Leike, Ku, Zhiqiang, Xiong, Wei, Jaijyan, Dabbu, Zhu, Hua, Wang, Dai, McLellan, Jason S., Zhang, Ningyan, Fu, Tong-Ming, An, Zhiqiang
• Format: Journal Article
• Language: English
• Published: San Francisco Public Library of Science 03.08.2020; Public Library of Science (PLoS)
• Subjects: Amino acids; Antibodies; Antigenic determinants; Antigens; Binding; Biochemistry; Biology and Life Sciences; Care and treatment; Congenital diseases; Crystal structure; Cytomegalovirus; Cytomegalovirus infections; Development and progression; Electron microscopy; Epitopes; Fab; Fibroblasts; Genomes; Glycoprotein B; Glycoproteins; Health aspects; Infections; Laboratories; Medicine; Medicine and Health Sciences; Membrane fusion; Membranes; Monoclonal antibodies; Morbidity; N-Terminus; Neonates; Neutralization; Neutralizing; Proteins; Recognition; Research and Analysis Methods; Supervision; Transplants & implants; Trimers; Vaccines; Viral infections; United States; United States > US; Texas; New Jersey
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1008736

Human cytomegalovirus (HCMV) is one of the main causative agents of congenital viral infection in neonates. HCMV infection also causes serious morbidity and mortality among organ transplant patients. Glycoprotein B (gB) is a major target for HCMV neutralizing antibodies, yet the underlying neutralization mechanisms remain largely unknown. Here we report that 3-25, a gB-specific monoclonal antibody previously isolated from a healthy HCMV-positive donor, efficiently neutralized 14 HCMV strains in both ARPE-19 cells and MRC-5 cells. The core epitope of 3-25 was mapped to a highly conserved linear epitope on antigenic domain 2 (AD-2) of gB. A 1.8 Å crystal structure of 3-25 Fab in complex with the peptide epitope revealed the molecular determinants of 3-25 binding to gB at atomic resolution. Negative-staining electron microscopy (EM) 3D reconstruction of 3-25 Fab in complex with de-glycosylated postfusion gB showed that 3-25 Fab fully occupied the gB trimer at the N-terminus with flexible binding angles. Functionally, 3-25 efficiently inhibited HCMV infection at a post-attachment step by interfering with viral membrane fusion, and restricted post-infection viral spreading in ARPE-19 cells. Interestingly, bivalency was required for HCMV neutralization by AD-2 specific antibody 3-25 but not the AD-4 specific antibody LJP538. In contrast, bivalency was not required for HCMV binding by both antibodies. Taken together, our results reveal the structural basis of gB recognition by 3-25 and demonstrate that inhibition of viral membrane fusion and a requirement of bivalency may be common for gB AD-2 specific neutralizing antibody.