Thermodynamic dissection of the interface between HIV-1 gp41 heptad repeats reveals cooperative interactions and allosteric effects

• Published in: Archives of biochemistry and biophysics 2020-07, Vol.688 (C), p.108401-108401, Article 108401
• Main Authors: Jurado, Samuel, Cano-Muñoz, Mario, Polo-Megías, Daniel, Conejero-Lara, Francisco, Morel, Bertrand
• Format: Article
• Language: English
• Subjects: Binding affinity; Calorimetry; Coiled-coil; Fusion inhibitors; Peptides
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/j.abb.2020.108401

HIV-1 glycoprotein 41 (gp41) mediates fusion between virus and target cells by folding into a fusion active state, in which the C-terminal heptad repeat (CHR) regions associate externally to the N-terminal heptad repeat (NHR) trimer and form a very stable six-helix bundle coiled-coil structure. Therefore, interfering with the NHR-CHR interaction of gp41 is a promising therapeutic approach against HIV-1. However, a full understanding of the molecular and mechanistic details of this interaction is still incomplete. Here, we use single-chain, chimeric proteins (named covNHR) that reproduce accurately the CHR-NHR interactions to analyze the binding thermodynamics of several peptides with different length from the CHR region. The results indicate that cooperative binding involving two or more pockets of the NHR groove is necessary to obtain relevant affinities and that the binding energy is broadly distributed along the interface, underlining a crucial role of a middle pocket to achieve tight binding. In contrast, targeting only the deep hydrophobic pocket is insufficient to achieve significant affinity. Moreover, calorimetry experiments in combination with limited proteolysis performed using a mutant with occluded binding in the N-terminal pocket reveal the existence of an allosteric communication between the different regions. This study is the first detailed thermodynamic dissection of the NHR-CHR interaction in gp41 and contributes therefore to a better understanding of HIV fusion. These results are relevant for the development of potential fusion inhibitors. •Targeting only the hydrophobic pocket is not sufficient from the point of view of an inhibitory drug.•The number of interaction sites is highly relevant to obtain high affinity.•Binding energy is distributed throughout the NHR-CHR interface.•Allosteric effects are propagated through the NHR coiled-coil structure.