Journal Article

Kinetically coupled folding of a single HIV-1 glycoprotein 41 complex in viral membrane fusion and inhibition

Jiao, Junyi, Gao, Ying, Zhang, Yongli, Ma, Lu, Rebane, Aleksander A.

2015

Overview

Significance Enveloped viruses infect cells via fusion of viral and host cell membranes mediated by highly conserved fusion proteins. HIV-1 glycoprotein 41 (gp41) represents a family of fusion proteins with similar structures and fusion mechanisms. They couple their energetic folding to draw two membranes close for fusion, forming trimers of helical hairpins. Yet, the energy release, force generation, and kinetics associated with folding of these proteins are poorly quantified. We found that gp41 hairpins fold sequentially but in a kinetically coupled manner and that an anti-HIV drug blocked gp41 folding by a new mechanism. As major proteins on viral surfaces, fusion proteins are primary targets for vaccine development and fusion inhibitors to intervene in major infectious diseases such as AIDS, Ebola, and influenza. HIV-1 glycoprotein 41 (gp41) mediates viral entry into host cells by coupling its folding energy to membrane fusion. Gp41 folding is blocked by fusion inhibitors, including the commercial drug T20, to treat HIV/AIDS. However, gp41 folding intermediates, energy, and kinetics are poorly understood. Here, we identified the folding intermediates of a single gp41 trimer-of-hairpins and measured their associated energy and kinetics using high-resolution optical tweezers. We found that folding of gp41 hairpins was energetically independent but kinetically coupled: Each hairpin contributed a folding energy of ∼−23 k BT, but folding of one hairpin successively accelerated the folding rate of the next one by ∼20-fold. Membrane-mimicking micelles slowed down gp41 folding and reduced the stability of the six-helix bundle. However, the stability was restored by cooperative folding of the membrane-proximal external region. Surprisingly, T20 strongly inhibited gp41 folding by actively displacing the C-terminal hairpin strand in a force-dependent manner. The inhibition was abolished by a T20-resistant gp41 mutation. The energetics and kinetics of gp41 folding established by us provides a basis to understand viral membrane fusion, infection, and therapeutic intervention.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Algorithms / Amino Acid Sequence / Anti-HIV Agents - pharmacology / antiretroviral agents / Biological Sciences / cell membranes / Cells / Cloning, Molecular / drugs / Energy / Glycoproteins / HIV / HIV Envelope Protein gp41 - chemistry / HIV Envelope Protein gp41 - genetics / HIV Envelope Protein gp41 - metabolism / HIV Envelope Protein gp41 - ultrastructure / HIV-1 - metabolism / Human immunodeficiency virus / Human immunodeficiency virus 1 / influenza / Kinetics / Likelihood Functions / membrane fusion / Membranes / Models, Molecular / Molecular Sequence Data / Mutation / Optical Tweezers / Peptide Fragments / PNAS Plus / Protein Folding - drug effects / vaccine development / viral proteins / Virus Internalization / viruses