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Structural and Thermodynamic Basis of Epitope Binding by Neutralizing and Nonneutralizing Forms of the Anti-HIV-1 Antibody 4E10

DOI: 10.1128/JVI.01793-15 DOI Help
PMID: 26378169 PMID Help

Authors: Edurne Rujas (University of Tokyo) , Naveed Gulzar (Simon Fraser University) , Koldo Morante (University of Tokyo) , Kouhei Tsumoto (University of Tokyo) , Jamie K. Scott (Simon Fraser University) , José L. Nieva (University of the Basque Country) , Jose M. M. Caaveiro (University of Tokyo)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Virology , VOL 89 (23) , PAGES 11975 - 11989

State: Published (Approved)
Published: December 2015

Open Access Open Access

Abstract: The 4E10 antibody recognizes the membrane-proximal external region (MPER) of the HIV-1 Env glycoprotein gp41 transmembrane subunit, exhibiting one of the broadest neutralizing activities known to date. The neutralizing activity of 4E10 requires solvent-exposed hydrophobic residues at the apex of the complementarity-determining region (CDR) H3 loop, but the molecular basis for this requirement has not been clarified. Here, we report the cocrystal structures and the energetic parameters of binding of a peptide bearing the 4E10-epitope sequence (4E10ep) to nonneutralizing versions of the 4E10 Fab. Nonneutralizing Fabs were obtained by shortening and decreasing the hydrophobicity of the CDR-H3 loop (termed ΔLoop) or by substituting the two tryptophan residues of the CDR-H3 apex with Asp residues (termed WDWD), which also decreases hydrophobicity but preserves the length of the loop. The analysis was complemented by the first crystal structure of the 4E10 Fab in its ligand-free state. Collectively, the data ruled out major conformational changes of CDR-H3 at any stage during the binding process (equilibrium or transition state). Although these mutations did not impact the affinity of wild-type Fab for the 4E10ep in solution, the two nonneutralizing versions of 4E10 were deficient in binding to MPER inserted in the plasma membrane (mimicking the environment faced by the antibody in vivo). The conclusions of our structure-function analysis strengthen the idea that to exert effective neutralization, the hydrophobic apex of the solvent-exposed CDR-H3 loop must recognize an antigenic structure more complex than just the linear α-helical epitope and likely constrained by the viral membrane lipids

Subject Areas: Biology and Bio-materials

Instruments: I02-Macromolecular Crystallography

Added On: 18/11/2015 14:06

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