Origins of Resistance to the HIVgp41 Viral Entry Inhibitor T20

Peptide T20, which targets the HIV protein gp41, represents the first approved member of the class of HIV drugs known as membrane fusion inhibitors. However, mechanisms which lead to resistance through clinical use of T20 are not well-understood because the structure of the bound complex remains undetermined. In this report, an atomic-level model of a T20 gp41 complex embedded in an explicit DOPC membrane was constructed, and molecular dynamics simulations, followed by binding energy analysis (MM-GBSA method), were performed to delineate structural and energetic features that contribute to drug resistance. Per-residue binding footprints for T20 with wild-type gp41 reveal strong intermolecular van der Waals, Coulombic, and H-bond interactions in striking agreement with clinically observed resistance patterns. In addition, seven deleterious gp41 point mutations (L33Q, L33S, G36V, I37K, V38E, Q40H, and Q40K) were simulated, and all correctly exhibited decreases in the level of binding, including the fact that L33Q and Q40K are most detrimental. Six of the seven simulations yield good quantitative agreement (r(2) = 0.72; N = 6) with available experimental fold resistance data. Results from energy decomposition, heat map analysis, and differential (mutant minus wild-type) footprinting indicate the following. (1) Mutations disrupt intermolecular H-bonding and reduce the level of favorable contact with gp41 at M19. (2) Charged mutations (I37K, Q40K, and V38E) lead to significant Coulombic changes that weaken favorable van der Waals interactions. (3) Q40K is more detrimental than I37K because of interaction differences with a polar/charged patch on T20 in the initial (wild-type) state. (4) Resistance for L33S versus L33Q likely involves side chain packing differences in the final (mutated) state. A valuable finding of the work involves identification of favorable interactions among the C-terminal end of T20 (WNWF motif), residues on gp41 (including the fusion peptide), and headgroups in the adjacent membrane. The results suggest a complete T20 binding site would contribute to a stable complex, which could help to explain why prior studies, which employed truncated gp41 constructs, reported that C-terminal T20 residues may not interact with gp41. A hypothesis resulting from this study is that peptides could be designed to increase the level of favorable contact with both the membrane and gp41 which would lead to enhanced activity.