MPER

The binding of the human immunodeficiency virus (HIV-1) envelope glycoprotein (Env) trimer ((gp120/gp41)3) to the receptors CD4 and CCR5 triggers virus entry into host cells. To identify Env regions that respond to CCR5 binding, HIV-1 was serially passaged on a CD4-positive canine cell line expressing progressively lower levels of CCR5. HIV-1 replication was observed in cells expressing ~1300 CCR5 molecules/cell. Env changes that conferred this low-CCR5 replication phenotype were located outside of the known CCR5-binding region of the gp120 Env subunit and did not apparently increase CCR5 binding affinity...

Broadly Cross clade Neutralizing (BCN) antibodies are recognized as potential therapeutic tools and leads for the design of a vaccine that can protect human beings against various clades of Human Immunodeficiency Virus (HIV). In the present study, we screened plasma of 88 HIV-1 infected ART naïve individuals for their neutralization potential using a standard panel of 18 pseudoviruses belonging to different subtypes and different levels of neutralization. We identified 12 samples with good breadth of neutralization (neutralized >90% of the viruses)...

PURPOSE OF REVIEW: We summarize the latest research on the progress to understand the neutralizing epitopes present within the membrane proximal external region (MPER) of the HIV-1 fusion protein subunit gp41. RECENT FINDINGS: The HIV-1 fusion protein subunit gp41 contains a highly conserved sequence that is essential for membrane fusion and targeted by broadly neutralizing antibodies such as 2F5, 4E10, Z13e1, and 10E8. These antibodies recognize a linear gp41 epitope with high affinity, but require additional hydrophobic sequences present in their heavy chain CDR3 for neutralization...

A limited number of sites on the HIV-1 Envelope protein are vulnerable to broadly neutralizing antibodies (bnAbs). One of these sites, the membrane proximal external region (MPER), is located at the C-terminus of the gp41 ectodomain (gp41ecto). This highly conserved sequence is bound by several well-characterized bnAbs. Efforts to produce a gp41 immunogen are in part hampered by the MPER's hydrophobicity and propensity to induce aggregation. We sought to produce a DNA vaccine expressing a gp41ecto that is both secreted from mammalian cells and maintains binding by bnAbs to the MPER...

The exceptional breadth of broadly neutralizing antibodies (bNAbs) against the membrane-proximal external region (MPER) of the transmembrane protein gp41 makes this class of antibodies an ideal model to design HIV vaccines. From a practical point of view, however, the preparation of vaccines eliciting bNAbs is still a major roadblock that limits their clinical application. Fresh mechanistic insights are necessary to develop more effective strategies. In particular, the function of the unusually long complementarity-determining region three of the heavy chain (CDRH3) of 4E10, an anti-MPER bNAb, is an open question that fascinates researchers in the field...

The transmembrane envelope (TM) protein gp41 of the human immunodeficiency virus-1 (HIV-1) plays an important role during virus infection inducing the fusion of the viral and cellular membranes. In addition, there are indications that the TM protein plays a role in the immunopathogenesis leading to the acquired immunodeficiency syndrome (AIDS). Inactivated virus particles and recombinant gp41 have been reported to inhibit lymphocyte proliferation, as well as to alter cytokine release and gene expression. The same was shown for a peptide corresponding to a highly conserved domain of all retroviral TM proteins, the immunosuppressive domain...

Broadly neutralizing antibodies (bNAbs) have provided valuable insights into the humoral immune response to HIV-1. While rationally designed epitope scaffolds and well-folded gp140 trimers have been proposed as vaccine antigens, a comparative understanding of their antibody responses has not yet been established. In this study, we probed antibody responses to the N332 supersite and the membrane-proximal external region (MPER) in the context of heterologous protein scaffolds and native-like gp140 trimers. Ferritin nanoparticles and fragment crystallizable (Fc) regions were utilized as multivalent carriers to display scaffold antigens with grafted N332 and MPER epitopes, respectively...

The membrane proximal external region (MPER) of HIV-1 gp41 is targeted by broadly neutralizing antibodies (bnAbs) 4E10 and 10E8. In this proof-of-concept study, we evaluated a novel multi-immunogen vaccine strategy referred to as Incremental, Phased Antigenic Stimulation for Rapid Antibody Maturation (IPAS-RAM) to induce 4E10/10E8-like bnAbs. Rabbits were immunized sequentially, but in a phased manner, with three immunogens that are progressively more native (gp41-28×3, gp41-54CT, and rVV-gp160DH12). Although nAbs were not induced, epitope-mapping analyses indicated that IPAS-RAM vaccination was better able to target antibodies towards the 4E10/10E8 epitopes than homologous prime-boost immunization using gp41-28×3 alone...

Among broadly neutralizing antibodies to HIV, 10E8 exhibits greater neutralizing breadth than most. Consequently, this antibody is the focus of prophylactic/therapeutic development. The 10E8 epitope has been identified as the conserved membrane proximal external region (MPER) of gp41 subunit of the envelope (Env) viral glycoprotein and is a major vaccine target. However, the MPER is proximal to the viral membrane and may be laterally inserted into the membrane in the Env prefusion form. Nevertheless, 10E8 has not been reported to have significant lipid-binding reactivity...

PURPOSE OF REVIEW: We summarize the latest research on the progress to understand the neutralizing epitopes present within the membrane proximal external region (MPER) of the HIV-1 fusion protein subunit gp41. RECENT FINDINGS: The HIV-1 fusion protein subunit gp41 contains a highly conserved sequence that is essential for membrane fusion and targeted by broadly neutralizing antibodies such as 2F5, 4E10, Z13e1, and 10E8. These antibodies recognize a linear gp41 epitope with high affinity, but require additional hydrophobic sequences present in their heavy chain CDR3 for neutralization...

The HIV broadly neutralizing antibody 2F5 targets the transiently exposed epitope in the membrane proximal external region (MPER) of HIV-1 gp41, by a two-step mechanism involving the viral membrane and this viral glycoprotein. It was recently shown that 2F5 conjugation with a cholesterol moiety outside of the antibody paratope substantially increases its antiviral activity. Additionally, the antiviral activity of D5, a human antibody that binds to the N-terminal heptad repeat (NHR) of gp41 and lacks membrane binding, was boosted by the same cholesterol conjugation...

A comprehensive understanding of the regions on HIV-1 envelope trimers targeted by broadly neutralizing antibodies may contribute to rational design of an HIV-1 vaccine. We previously identified a participant in the CAPRISA cohort, CAP248, who developed trimer-specific antibodies capable of neutralizing 60% of heterologous viruses at three years post-infection. Here, we report the isolation by B cell culture of monoclonal antibody CAP248-2B, which targets a novel membrane proximal epitope including elements of gp120 and gp41...

The mechanism by which the HIV-1 MPER epitope is recognized by the potent neutralizing antibody 10E8 at membrane interfaces remains poorly understood. To solve this problem, we have optimized a 10E8 peptide epitope and analyzed the structure and binding activities of the antibody in membrane and membrane-like environments. The X-ray crystal structure of the Fab-peptide complex in detergents revealed for the first time that the epitope of 10E8 comprises a continuous helix spanning the gp41 MPER/transmembrane domain junction (MPER-N-TMD; Env residues 671-687)...

The HIV-1 envelope protein (Env) has evolved to subvert the host immune system, hindering viral control by the host. The tryptophan metabolic enzyme kynureninase (KYNU) is mimicked by a portion of the HIV Env gp41 membrane proximal region (MPER) and is cross-reactive with the HIV broadly neutralizing Ab (bnAb) 2F5. Molecular mimicry of host proteins by pathogens can lead to autoimmune disease. In this article, we demonstrate that neither the 2F5 bnAb nor HIV MPER-KYNU cross-reactive Abs elicited by immunization with an MPER peptide-liposome vaccine in 2F5 bnAb VHDJH and VLJL knock-in mice and rhesus macaques modified KYNU activity or disrupted tissue tryptophan metabolism...

Definition of the key parameters mediating effective antibody blocking of HIV-1 acquisition within mucosal tissue may prove critical to effective vaccine development and the prophylactic use of monoclonal antibodies. Although direct antibody-mediated neutralization is highly effective against cell-free virus, antibodies targeting different sites of envelope vulnerability may display differential activity against mucosal infection. Nonneutralizing antibodies (nnAbs) may also impact mucosal transmission events through Fc-gamma receptor (FcγR)-mediated inhibition...

We recently reported the discovery of a recombinant chimera, denoted DAVEI (dual-acting virucidal entry inhibitor), which is able to selectively cause specific and potent lytic inactivation of both pseudotyped and fully infectious human immunodeficiency virus (HIV-1) virions. The chimera is composed of the lectin cyanovirin-N (CVN) fused to the 20-residue membrane-proximal external region (MPER) of HIV-1 gp41. Because the Env gp120-binding CVN domain on its own is not lytic, we sought here to determine how the MPER(DAVEI) domain is able to endow the chimera with virolytic activity...

Most HIV-1 vaccines elicit neutralizing antibodies that are active against highly sensitive (tier-1) viruses or rare cases of vaccine-matched neutralization-resistant (tier-2) viruses, but no vaccine has induced antibodies that can broadly neutralize heterologous tier-2 viruses. In this study, we isolated antibodies from an HIV-1-infected individual that targeted the gp41 membrane-proximal external region (MPER) that may have selected single-residue changes in viral variants in the MPER that resulted in neutralization sensitivity to antibodies targeting distal epitopes on the HIV-1 Env...

The transitioning of the ectodomain of gp41 from a pre-hairpin to a six-helix bundle conformation is a crucial aspect of virus-cell fusion. To gain insight into the intermediary steps of the fusion process we have studied the pH and dodecyl phosphocholine (DPC) micelle dependent trimer association of gp41 by systematic deletion analysis of an optimized construct termed 17-172 (residues 528 to 683 of Env) that spans the fusion peptide proximal region (FPPR) to the membrane proximal external region (MPER) of gp41, by sedimentation velocity and double electron-electron resonance (DEER) EPR spectroscopy...

UNLABELLED: An effective preventive vaccine is highly sought after in order to stem the current HIV-1 pandemic. Both conservation of contiguous gp41 membrane-proximal external region (MPER) amino acid sequences across HIV-1 clades and the ability of anti-MPER broadly neutralizing antibodies (BNAbs) to block viral hemifusion/fusion establish the MPER as a prime vaccination target. In earlier studies, we described the development of an MPER vaccine formulation that takes advantage of liposomes to array the MPER on a lipid bilayer surface, paralleling its native configuration on the virus membrane while also incorporating molecular adjuvant and CD4 T cell epitope cargo...

The HIV-1 membrane proximal external region (MPER) that is targeted by several broadly neutralizing antibodies (BNAbs) has been considered a potential immunogen for vaccine development. However, to date the immunogenicity of these BNAb epitopes has not been made sufficiently adequate. In the present work, we used live attenuated Salmonella as a platform to present the HIV-1 MPER 10E8 epitope in the fimbriae. The insertion of the 10E8 epitope into the fimbriae had no significant influence on the expression and the absorption capacity of bacterial fimbriae, nor on the virulence and invasiveness of the attenuated Salmonella...