title: Asymmetric recognition of the HIV-1 trimer by broadly neutralizing antibody PG9.
abstract: PG9 is the founder member of an expanding family of glycan-dependent human antibodies that preferentially bind the HIV (HIV-1) envelope (Env) glycoprotein (gp) trimer and broadly neutralize the virus. Here, we show that a soluble SOSIP.664 gp140 trimer constructed from the Clade A BG505 sequence binds PG9 with high affinity (∼11 nM), enabling structural and biophysical characterizations of the PG9:Env trimer complex. The BG505 SOSIP.664 gp140 trimer is remarkably stable as assessed by electron microscopy (EM) and differential scanning calorimetry. EM, small angle X-ray scattering, size exclusion chromatography with inline multiangle light scattering and isothermal titration calorimetry all indicate that only a single PG9 fragment antigen-binding (Fab) binds to the Env trimer. An ∼18 Å EM reconstruction demonstrates that PG9 recognizes the trimer asymmetrically at its apex via contact with two of the three gp120 protomers, possibly contributing to its reported preference for a quaternary epitope. Molecular modeling and isothermal titration calorimetry binding experiments with an engineered PG9 mutant suggest that, in addition to the N156 and N160 glycan interactions observed in crystal structures of PG9 with a scaffolded V1/V2 domain, PG9 makes secondary interactions with an N160 glycan from an adjacent gp120 protomer in the antibody-trimer complex. Together, these structural and biophysical findings should facilitate the design of HIV-1 immunogens that possess all elements of the quaternary PG9 epitope required to induce broadly neutralizing antibodies against this region.
authors: Department of Integrative Structural and Computational Biology, International AIDS Vaccine Initiative Neutralizing Antibody Center, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors: Jean-Philippe
authors: JP
authors: Julien
authors: Jeong Hyun
authors: JH
authors: Lee
authors: Albert
authors: A
authors: Cupo
authors: Charles D
authors: CD
authors: Murin
authors: Ronald
authors: R
authors: Derking
authors: Simon
authors: S
authors: Hoffenberg
authors: Michael J
authors: MJ
authors: Caulfield
authors: C Richter
authors: CR
authors: King
authors: Andre J
authors: AJ
authors: Marozsan
authors: Per Johan
authors: PJ
authors: Klasse
authors: Rogier W
authors: RW
authors: Sanders
authors: John P
authors: JP
authors: Moore
authors: Ian A
authors: IA
authors: Wilson
authors: Andrew B
authors: AB
authors: Ward
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry*; D057134:Antibodies, Neutralizing / Q000737:chemistry*; D002460:Cell Line; D000939:Epitopes / Q000737:chemistry*; D015483:HIV Antibodies / Q000737:chemistry*; D015497:HIV-1 / Q000737:chemistry*; D006801:Humans; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D014961:X-Ray Diffraction; D054299:env Gene Products, Human Immunodeficiency Virus / Q000737:chemistry*
chemical_list: D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing; D000939:Epitopes; D015483:HIV Antibodies; D054299:env Gene Products, Human Immunodeficiency Virus