Article

Broadly Neutralizing Anti-HIV Antibody 4E10 Recognizes a Helical Conformation of a Highly Conserved Fusion-Associated Motif in gp41

Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Immunity (Impact Factor: 21.56). 03/2005; 22(2):163-73. DOI: 10.1016/j.immuni.2004.12.011
Source: PubMed

ABSTRACT

Broadly neutralizing monoclonal antibodies to HIV-1 are rare but invaluable for vaccine design. 4E10 is the broadest neutralizing antibody known and recognizes a contiguous and highly conserved epitope in the membrane-proximal region of gp41. The crystal structure of Fab 4E10 was determined at 2.2 A resolution in complex with a 13-residue peptide containing the gp41 core epitope (NWFDIT). The bound peptide adopts a helical conformation in which the key contact residues, TrpP672, PheP673, IleP675, and ThrP676, map to one face of the helix. The peptide binds in a hydrophobic pocket that may emulate its potential interaction with the host cell membrane. The long CDR H3 of the antibody extends beyond the bound peptide in an orientation that suggests that its apex could contact the viral membrane when 4E10 is bound to its membrane-proximal epitope. These structural insights should assist in the design of immunogens to elicit 4E10-like neutralizing responses.

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    • "Studies with the 2F5, 4E10, Z13e1, and 10E8 mAbs have helped elucidate the dynamic movement that the MPER normally undergoes in the processes of membrane fusion and viral entry [22,23,24,25,26,27,28,29,30,31]. By bending the MPER at a hinge (2F5, 4E10, and 10E8) or rigidifying the structure of the MPER (Z13e1) [26,27,28,29,31], the MPER-directed antibodies appear to effect neutralization by interfering with the post-CD4 binding steps necessary for formation of the pre-hairpin intermediate [32], most likely via a required initial interaction of their H3 loops with the viral membrane [26,33,34]. "
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    ABSTRACT: The development of an effective AIDS vaccine has been a formidable task, but remains a critical necessity. The well conserved membrane-proximal external region (MPER) of the HIV-1 gp41 glycoprotein is one of the crucial targets for AIDS vaccine development, as it has the necessary attribute of being able to elicit antibodies capable of neutralizing diverse isolates of HIV. Guided by X-ray crystallography, molecular modeling, combinatorial chemistry, and powerful selection techniques, we designed and produced six combinatorial libraries of chimeric human rhinoviruses (HRV) displaying the MPER epitopes corresponding to mAbs 2F5, 4E10, and/or Z13e1, connected to an immunogenic surface loop of HRV via linkers of varying lengths and sequences. Not all libraries led to viable chimeric viruses with the desired sequences, but the combinatorial approach allowed us to examine large numbers of MPER-displaying chimeras. Among the chimeras were five that elicited antibodies capable of significantly neutralizing HIV-1 pseudoviruses from at least three subtypes, in one case leading to neutralization of 10 pseudoviruses from all six subtypes tested. Optimization of these chimeras or closely related chimeras could conceivably lead to useful components of an effective AIDS vaccine. While the MPER of HIV may not be immunodominant in natural infection by HIV-1, its presence in a vaccine cocktail could provide critical breadth of protection.
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    • "A number of groups have isolated several monoclonal antibodies (mAbs) that can neutralize a variety of HIV-1 isolates [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]. Among those mAbs, 2F5, 4E10, Z13 and the recently reported 10E8 are shown to target conserved epitopes within the membraneproximal external region (MPER) of gp41 [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]; The isolation of these and other broadly neutralizing antibodies (b12, 2G12, VRC01, CH01 to CH04, PG9, PG16) is a milestone in the field. The epitopes located at the MPER of gp41 recognized by broadly neutralizing mAbs 2F5 and 4E10 are promising targets for vaccine design. "
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    • "However, rodents, including mice, lack the ability to produce antibodies with long CDR3 loops [24]. Since these loops are important features of several known broadly neutralizing antibodies [3,2627282930, the rodent models have a clear disadvantage when screening for immunogenicity. The rabbit model, being a lagomorph and a larger animal, may more closely resemble the macaque model and still maintain the advantages of being less expensive, easy to handle and with large blood volumes to work with. "
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