Abstract
The prefusion conformation of HIV-1 envelope protein (Env) is recognized by most broadly neutralizing antibodies (bnAbs). Studies showed that alterations of its membrane-related components, including the transmembrane domain (TMD) and cytoplasmic tail (CT), can reshape the antigenic structure of the Env ectodomain. Using nuclear magnetic resonance (NMR) spectroscopy, we determine the structure of an Env segment encompassing the TMD and a large portion of the CT in bicelles. The structure reveals that the CT folds into amphipathic helices that wrap around the C-terminal end of the TMD, thereby forming a support baseplate for the rest of Env. NMR dynamics measurements provide evidences of dynamic coupling across the TMD between the ectodomain and CT. Pseudovirus-based neutralization assays suggest that CT-TMD interaction preferentially affects antigenic structure near the apex of the Env trimer. These results explain why the CT can modulate the Env antigenic properties and may facilitate HIV-1 Env-based vaccine design.
Highlights
The prefusion conformation of HIV-1 envelope protein (Env) is recognized by most broadly neutralizing antibodies
We found that the Kennedy sequence (KS) was completely unstructured according to the nuclear magnetic resonance (NMR) data and that removal of its central region did not affect the protein structure (Supplementary Fig. 2)
Hydrophobicity/hydrophilicity swapping of the key transmembrane domain (TMD) residues in the cytoplasmic tail (CT)–TMD interface generated a mutant (TMD-ct) that, while still sensitive to VRC01, was completely resistant to the trimer-specific broadly neutralizing antibodies (bnAbs) and substantially sensitive to b6, 3791, and 17b (Fig. 4e). These results suggest that disrupting the packing interface between the TMD and CT can destabilize the Env ectodomain and shift it to an open conformation[10,40,41], further supporting our previous notion that the CT can modulate the antigenic structure of the Env trimer[5]
Summary
The prefusion conformation of HIV-1 envelope protein (Env) is recognized by most broadly neutralizing antibodies (bnAbs). Studies showed that alterations of its membrane-related components, including the transmembrane domain (TMD) and cytoplasmic tail (CT), can reshape the antigenic structure of the Env ectodomain. Pseudovirus-based neutralization assays suggest that CT-TMD interaction preferentially affects antigenic structure near the apex of the Env trimer. Several studies demonstrated that alterations of its membrane-related components, including the transmembrane domain (TMD) and cytoplasmic tail (CT), can reshape the antigenic structure of the Env ectodomain exposed outside of viral membrane[5,8,9], suggesting that there are intricate interconnections among them. Earlier studies suggested that the CT forms three membrane-bound amphipathic helices in an extended conformation[19,20] These structures are very informative about the secondary structures of the CT, but they fall short of explaining how truncation in the CT can influence the antigenic structure of the ectodomain on the opposite side of the membrane[5,21,22]. We find that the CT adopts a structure different from the previous model[19] that can explain the physical coupling between the CT and the ectodomain
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