Properties and mechanism of action of a 17 amino acid, V3 loop-specific microantibody that binds to and neutralizes human immunodeficiency virus type 1 virions.

Abstract

Only two virus-neutralizing peptide microantibodies (MicroAbs) have been described and little is known about their mode of action. This report concerns a 17 amino acid cyclized MicroAb, derived from the third complementarity-determining region of the heavy chain of MAb F58 (IgG1), that recognizes the same minimum epitope in the V3 loop of the gp120 envelope protein of human immunodeficiency virus type 1 (HIV-1) as the MAb. The MicroAb was able to bind to and neutralize free virus particles. It was up to 5-fold more efficient in mass terms than F58 IgG and its neutralization rate on a molar basis was only 32-fold lower. The mechanism of neutralization of the MicroAb was also investigated. A high level of neutralization (99 %) occurred without any significant decrease in attachment of virus to target C8166 cells. Neutralized virus attached to CD4, the HIV-1 primary receptor. Fusion of virions to cells was partially inhibited by the MicroAb, whereas F58 IgG has been shown to inhibit fusion significantly. Thus, neutralization by the MicroAb appears to be mediated, at least in part, by inhibition of fusion. Control peptides, in which the tyrosine at position 5 or 6 was deleted or changed to phenylalanine, showed no antiviral activity, attesting to the specificity of interaction of the MicroAb with the virion. It therefore appears that the MicroAb acts like an immunoglobulin. The data also show that the MicroAb/MAb F58 epitope on the V3 loop is not involved in attachment of virus to CD4 but is required for subsequent events in early infection.

Properties of a neutralizing antibody that recognizes a conformational form of epitope ERDRD in the gp41 C-terminal tail of human immunodeficiency virus type 1

“…Of six neutralizing antibodies tested, two (MAbs ICR39.13g and b12) give PAN at 37 mC for a prolonged period and probably until fusion takes place, but the others (the ERDRD-specific IgG, MAbs ICR39.3b, ICR41.1i, F58 and the F58 MicroAb) enact PAN only for a much shorter period of time (Fig. 3 b ; Armstrong & Dimmock, 1996 ;Armstrong et al, 1996 ;Jackson et al, 1999 ;unpublished data). Such antibodies provide the means to dissect out the complex events that constitute the fusion process, particularly as they recognize various different parts of the envelope protein, including the CD4-binding site region (ICR39.3b, MAbs ICR39.13g and b12), sequences within the V3 loop (ICR41.1i, F58 and its MicroAb) and the gp41 loop structure (ERDRD-specific IgG).…”

“…b12 IgG ;McInerney et al, 1997) or have a second, slower component (e.g. MAb F58 ; Jackson et al, 1999). Rate constants (kK neut ) for the neutralization of HIV-1 IIIB and closely related viruses range from 3n5i10& M −" s −" for MAb b12 to 6n3i10# M −" s −" for MAb ICR39.3b (Krause et al, 1997).…”

“…Individual HIV-1-neutralizing IgGs vary in their ability to cause PAN, some acting at any temperature up to 37 mC up to the moment virus fuses with the cell, some only at temperatures of 24 mC and below, while one was unable to give PAN at all (Armstrong & Dimmock, 1996 ;Armstrong et al, 1996 ;Jackson et al, 1999).…”

Heterogeneity of Envelope Molecules Shown by Different Sensitivities to Anti‐V3 Neutralizing Antibody and CXCR4 Antagonist Regulates the Formation of Multiple‐Site Binding of HIV‐1

“…The V3 domain of gp120 is thought to be the primary determinant of coreceptor (CXCR4 or CCR5) usage (6) together with the V1/V2 contribution (7,9,19), and a single amino acid change in V3 could switch the viral coreceptor usage (3,14,28,33). Anti-V3 neutralization is proposed to operate mainly by high-occupancy of V3 (16) and/or by steric alteration of the envelope (1,10,11,15). Viruses with many fgp120 would need more anti-V3 antibodies to be highly occupied and neutralized than those with few fgp120.…”

A Synthetic Camel Anti‐Lysozyme Peptide Antibody (Peptibody) with Flexible Loop Structure Identified by High‐Resolution Affinity Mass Spectrometry

“…[16] Such peptide antibodies, comprising around 20 amino acids, have been successfully designed and explored, for example, for HIV-protein antigens. [16,17] Cyclic peptide epitopes have been shown previously to exhibit high affinity, possibly by stabilising secondary structures essential for recognition. [18,19] We have designed a 26-amino acid residue peptide antibody loop ("peptibody" 1 ) by addition of N-and C-terminal cysteine residues for cyclisation that has high, native-like affinity to the active site of HEL.…”