Cryo-EM structures elucidate neutralizing mechanisms of anti-chikungunya human monoclonal antibodies with therapeutic activity.
Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes severe acute and chronic disease in humans. Although highly inhibitory murine and human monoclonal antibodies (mAbs) have been generated, the structural basis of their neutralizing activity remains poorly characterized. Here, we determined the cryo-EM structures of chikungunya virus-like particles complexed with antibody fragments (Fab) of two highly protective human mAbs, 4J21 and 5M16, that block virus fusion with host membranes. Both mAbs bind primarily to sites within the A and B domains, as well as to the B domain's β-ribbon connector of the viral glycoprotein E2. The footprints of these antibodies on the viral surface were consistent with results from loss-of-binding studies using an alanine scanning mutagenesis-based epitope mapping approach. The Fab fragments stabilized the position of the B domain relative to the virus, particularly for the complex with 5M16. This finding is consistent with a mechanism of neutralization in which anti-CHIKV mAbs that bridge the A and B domains impede movement of the B domain away from the underlying fusion loop on the E1 glycoprotein and therefore block the requisite pH-dependent fusion of viral and host membranes.
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907;
Feng
F
Long
Integral Molecular, Inc., Philadelphia, PA 19104;
Rachel H
RH
Fong
Departments of Medicine, Molecular Microbiology, Pathology, and Immunology, Washington University School of Medicine, St. Louis, MO 63110;
Stephen K
SK
Austin
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907;
Zhenguo
Z
Chen
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907;
Thomas
T
Klose
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907;
Andrei
A
Fokine
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907;
Yue
Y
Liu
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907;
Jason
J
Porta
Department of Pediatrics, Vanderbilt University, Nashville, TN 37232;
Gopal
G
Sapparapu
VLP Therapeutics, LLC, Gaithersburg, MD 20878;
Wataru
W
Akahata
Integral Molecular, Inc., Philadelphia, PA 19104;
Benjamin J
BJ
Doranz
Department of Pediatrics, Vanderbilt University, Nashville, TN 37232; Departments of Pathology, Microbiology, and Immunology, Vanderbilt University, Nashville, TN 37232; Vanderbilt Vaccine Center, Vanderbilt University Medical Center, Vanderbilt University, Nashville, TN 37232.
James E
JE
Crowe
Departments of Medicine, Molecular Microbiology, Pathology, and Immunology, Washington University School of Medicine, St. Louis, MO 63110;
Michael S
MS
Diamond
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907; mr@purdue.edu.
Michael G
MG
Rossmann
D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology* / Q000627:therapeutic use; D057134:Antibodies, Neutralizing / Q000737:chemistry / Q000276:immunology* / Q000627:therapeutic use; D065632:Chikungunya Fever / Q000628:therapy*; D002646:Chikungunya virus / Q000276:immunology*; D020285:Cryoelectron Microscopy / Q000379:methods*; D006801:Humans; D011487:Protein Conformation
D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing
chikungunya virus-antibody complexes; cryo-electron microscopy structure; neutralizing mechanism; viral fusion inhibition