Antigenic analysis of the HIV-1 envelope trimer implies small differences between structural states 1 and 2

J Biol Chem. 2022 Apr;298(4):101819. doi: 10.1016/j.jbc.2022.101819. Epub 2022 Mar 10.


The conformationally dynamic HIV-1 envelope trimer (Env) is the target of broadly neutralizing antibodies (bnAbs) that block viral entry. Single-molecule Förster resonance energy transfer (smFRET) has revealed that HIV-1 Env exists in at least three conformational states on the virion. Prior to complete host-receptor engagement (State 3), Env resides most prevalently in the smFRET-defined State 1, which is preferentially recognized by most bnAbs that are elicited by natural infection. smFRET has also revealed that soluble trimers containing prefusion-stabilizing disulfide and isoleucine-to-proline substitutions reside primarily in State 2, which is a required intermediate between States 1 and 3. While high-resolution Env structures have been determined for States 2 and 3, the structure of these trimers in State 1 is unknown. To provide insight into the State 1 structure, here we characterized antigenic differences between smFRET-defined states and then correlated these differences with known structural differences between States 2 and 3. We found that cell surface-expressed Env was enriched in each state using state-enriching antibody fragments or small-molecule virus entry inhibitors and then assessed binding to HIV-1 bnAbs preferentially binding different states. We observed small but consistent differences in binding between Env enriched in States 1 and 2, and a more than 10-fold difference in binding to Env enriched in these states versus Env enriched in State 3. We conclude that structural differences between HIV-1 Env States 1 and 3 are likely more than 10-fold greater than those between States 1 and 2, providing important insight into State 1.

Keywords: HIV-1; SOSIP; broadly neutralizing antibody; conformational change; flow cytometry; glycoprotein structure; intermediate conformations; smFRET.

MeSH terms

  • Broadly Neutralizing Antibodies / chemistry
  • Broadly Neutralizing Antibodies / metabolism
  • HIV Antibodies
  • HIV Infections*
  • HIV-1* / metabolism
  • Humans
  • Protein Conformation
  • env Gene Products, Human Immunodeficiency Virus* / chemistry
  • env Gene Products, Human Immunodeficiency Virus* / metabolism


  • Broadly Neutralizing Antibodies
  • HIV Antibodies
  • env Gene Products, Human Immunodeficiency Virus