Stable, uncleaved HIV-1 envelope glycoprotein gp140 forms a tightly folded trimer with a native-like structure

Area of Science:

• Virology
• Immunology
• Biochemistry

Background:

• The HIV-1 envelope spike protein complex, (gp120/gp41)3, mediates viral entry and is a key target for humoral immune responses.
• Developing recombinant vaccines faces challenges due to the tendency of the (gp120/gp41)3 complex to dissociate.
• Previous work demonstrated that stable, uncleaved HIV-1 gp140 trimers possess antigenic properties similar to native viral spikes.

Purpose of the Study:

• To investigate the structural stability and conformation of stable HIV-1 gp140 trimers.
• To address concerns that uncleaved gp140 proteins might adopt a non-native, postfusion conformation.
• To evaluate the impact of a flexible linker between gp120 and gp41 on trimer stability and structure.

Main Methods:

• Insertion of a flexible linker between gp120 and gp41 in stable gp140 trimers.
• Biochemical and antigenic property analysis of modified and unmodified gp140 trimers.
• CD4 binding assays to assess conformational states.
• Structural analysis of the gp41 ectodomain in modified and unmodified trimers.

Main Results:

• Modified gp140 trimers with a flexible linker exhibited biochemical and antigenic properties nearly identical to unmodified trimers.
• Both modified and unmodified trimers bound a single CD4 molecule per trimer, indicating occlusion of CD4 binding sites.
• An artificial trimer with gp120s tethered to a tag bound three CD4s and showed antigenicity similar to monomeric gp120.
• The gp41 ectodomain in both gp140 forms displayed a structure distinct from the postfusion conformation.

Conclusions:

• Uncleaved gp140 trimers from appropriate isolates adopt compact, native-like structures.
• The flexible linker did not induce a non-native conformation or affect CD4 binding properties.
• These stable gp140 trimers are suitable as candidate immunogens for HIV vaccine development.