Abstract:HIV-1 enters cells through binding between viral envelope glycoprotein (Env) and cellular receptors to initiate virus and cell fusion. HIV-1 Env precursor (gp160) is cleaved into two units noncovalently bound to form a trimer on virions, including a surface unit (gp120) and a transmembrane unit (gp41) responsible for virus binding and membrane fusion, respectively. The polar region (PR) at the N terminus of gp41 comprises 17 residues, including 7 polar amino acids. Previous studies suggested that the PR contri… Show more
“…We expect that the changes in the FPPR induce similar release of structural constraints that maintain the trimer in a closed conformation. Based on proximity of the FPPR to the CHR, is it likely that the FPPR substitutions affect the interaction between the two domains (28). The nature of the association between the MPER and other components of gp41, which can explain the structural basis for our observations, remains to be clarified.…”
Section: Discussionmentioning
confidence: 91%
“…In the unliganded form of Env (i.e., not bound to CD4), the FPPR appears to be conformationally flexible (25,26). Nevertheless, substitutions at some FPPR positions increase detachment of gp120 from virions (27,28), supporting the notion that this region contributes to structural stability of the trimer. We analyzed the historical changes in amino acid sequence of the FPPR among clade B viruses and tested the emerging variants for their fitness and antigenicity.…”
The error-prone replication machinery of HIV-1 continuously generates new variants of the envelope glycoproteins (Envs). Antibody selection pressures applied in the host can limit their persistence. The target specificity of antibodies elicited in different hosts varies considerably. Whether some specificities are shared and have affected the population-level evolution of Env structure is still unclear. We examined the historical changes in amino acid sequence of the gp41 fusion peptide proximal region (FPPR), which is not exposed on the Env trimer. For three FPPR positions, the residue found in the clade B ancestor was mainly replaced by alanine. However, the changes in alanine frequency at these positions between 1979 and 2016 followed different patterns; two positions maintained a historically-constant frequency whereas the third showed a gradual increase. To understand these patterns, we introduced alanine substitutions in the FPPR of primary HIV-1 strains and examined their fitness and antigenicity relative to the clade-ancestral form. The evolutionary patterns could not be explained by effects on Env fitness. Instead, the FPPR variants with a historically-constant alanine frequency exhibited a unique open-at-the-base conformation of the trimer that exposes partially-cryptic epitopes. These Envs were modestly but significantly more sensitive to poorly-neutralizing sera from HIV-infected individuals than the clade-ancestral form. Our findings suggest that weakly-neutralizing antibodies targeting the base of the trimer are commonly elicited. Such low-level antibody pressures do not exert catastrophic effects on the emerging variants but rather determine their set-point frequency in the population and historical patterns of change.
“…We expect that the changes in the FPPR induce similar release of structural constraints that maintain the trimer in a closed conformation. Based on proximity of the FPPR to the CHR, is it likely that the FPPR substitutions affect the interaction between the two domains (28). The nature of the association between the MPER and other components of gp41, which can explain the structural basis for our observations, remains to be clarified.…”
Section: Discussionmentioning
confidence: 91%
“…In the unliganded form of Env (i.e., not bound to CD4), the FPPR appears to be conformationally flexible (25,26). Nevertheless, substitutions at some FPPR positions increase detachment of gp120 from virions (27,28), supporting the notion that this region contributes to structural stability of the trimer. We analyzed the historical changes in amino acid sequence of the FPPR among clade B viruses and tested the emerging variants for their fitness and antigenicity.…”
The error-prone replication machinery of HIV-1 continuously generates new variants of the envelope glycoproteins (Envs). Antibody selection pressures applied in the host can limit their persistence. The target specificity of antibodies elicited in different hosts varies considerably. Whether some specificities are shared and have affected the population-level evolution of Env structure is still unclear. We examined the historical changes in amino acid sequence of the gp41 fusion peptide proximal region (FPPR), which is not exposed on the Env trimer. For three FPPR positions, the residue found in the clade B ancestor was mainly replaced by alanine. However, the changes in alanine frequency at these positions between 1979 and 2016 followed different patterns; two positions maintained a historically-constant frequency whereas the third showed a gradual increase. To understand these patterns, we introduced alanine substitutions in the FPPR of primary HIV-1 strains and examined their fitness and antigenicity relative to the clade-ancestral form. The evolutionary patterns could not be explained by effects on Env fitness. Instead, the FPPR variants with a historically-constant alanine frequency exhibited a unique open-at-the-base conformation of the trimer that exposes partially-cryptic epitopes. These Envs were modestly but significantly more sensitive to poorly-neutralizing sera from HIV-infected individuals than the clade-ancestral form. Our findings suggest that weakly-neutralizing antibodies targeting the base of the trimer are commonly elicited. Such low-level antibody pressures do not exert catastrophic effects on the emerging variants but rather determine their set-point frequency in the population and historical patterns of change.
“…Specifically, the N36/C34 complex showed 89% α-helices with a melting temperature ( T m ) value of 63 ℃, whereas the N36/C34 N145A complex showed 81% α-helices with a T m of 51 ℃. Because the recent studies suggested that the interactions between the FPPR of NHR and the TRM of CHR also critically determine the NHR-CHR interactions and HIV-1 entry [14,22,34], we further used the NHR-derived peptide N39, the inhibitor T20, and its N145A mutant as surrogates. As shown in Figure 4C-D, the N39/T20 complex displayed 53% α-helices with a T m of 43 ℃, but the α-helical content and T m of the N39/T-20 N145A complex could not be defined, which suggested that the N145A substitution disrupted the helical interaction between N39 and T20.…”
Entry of HIV-1 into target cells is mediated by its envelope (Env) glycoprotein composed of the receptor binding subunit gp120 and the fusion protein gp41. Refolding of the gp41 N- and C-terminal heptad repeats (NHR and CHR) into a six-helix bundle (6-HB) conformation drives the viral and cellular membranes in close apposition and generates huge amounts of energy to overcome the kinetic barrier leading to membrane fusion. In this study, we focused on characterizing the structural and functional properties of a single Asn-145 residue, which locates at the middle CHR site of gp41 and is extremely conserved among all the HIV-1, HIV-2, and simian immunodeficiency virus (SIV) isolates. By mutational analysis, we found that Asn-145 plays critical roles for Env-mediated cell-cell fusion and HIV-1 entry. As determined by circular dichroism (CD) spectroscopy and isothermal titration calorimetry (ITC), the substitution of Asn-145 with alanine (N145A) severely impaired the interactions between the NHR and CHR helices. Asn-145 was also verified to be important for the antiviral activity of CHR-derived peptide fusion inhibitors and served as a turn-point for the inhibitory potency. Intriguingly, Asn-145 could regulate the functionality of the M-T hook structure at the N-terminus of the inhibitors and displayed comparable activities with the C-terminal IDL anchor. Crystallographic studies further demonstrated the importance of Asn-145-mediated interhelical and intrahelical interactions in the 6-HB structure. Combined, the present results have provided valuable information for the structure-function relationship of HIV-1 gp41 and the structure-activity relationship of gp41-dependent fusion inhibitors.
“…Previous studies suggested that the PR participates in Env peptide-based membrane fusion ( 5 – 9 ); however, the function of the PR is not fully understood. We have reported that the PR is highly conserved and determines viral fusion and infectivity ( 10 ). We characterized three PR mutants ( 10 ) containing S534P/T536A, S534P/T536A/T538A or S534P, named M1, M3 or M4, respectively ( Fig.…”
mentioning
confidence: 99%
“…We have reported that the PR is highly conserved and determines viral fusion and infectivity ( 10 ). We characterized three PR mutants ( 10 ) containing S534P/T536A, S534P/T536A/T538A or S534P, named M1, M3 or M4, respectively ( Fig. 1A ).…”
Our previous mutagenesis study revealed that serine at position 534 of HIV-1 Env is critical for viral infectivity. We found that HIV-1 Env containing serine to proline mutation at position 534 (S534P) are incapable of supporting virus-cell and cell-cell fusion.
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