VRC01 gp120 complex

From Proteopedia

Revision as of 07:23, 27 November 2012

The crystal structure of VRC01 and VRC01-like antibodies are studied to define with characteristics are important in neutralizing HIV-1. (cite!)

Introduction

HIV-1 has a high level of antigenic and genetic diversity. HIV-1 has also evolved mechanisms to evade the humoral immune response. These aspects of HIV-1 have made it difficult to develop a vaccine. After several years of infection, 10 to 25% of HIV-1 infected individuals develop neutralizing antibodies. Some antibodies target the transmembrane gp41 molecules of the HIV-1 viral spike, however most target the surface protein gp120. (Wu) VRC01 and VRC01-like antibodies bind to gp120 and are able to neutralize about 90% of HIV-1 isolates. Structural analysis has shown which characteristics of antibodies are essential to its binding with gp120. (Kwong) Discovery of the structure of these antibodies can help develop an effective HIV-1 vaccine.

HIV-1 Neutralization

HIV-1 enters its host by binding viral gp120, a surface glycoprotein of HIV, to the host cell’s CD4 receptor. This interaction induces conformational changes in gp120. (Wu) This conformational change results in the exposure of a binding site for the co-receptor, usually CCR5 OR CXCR4. (Li) The conformational changes also result in the formation of a pre-hairpin intermediate conformation in which gp41, a transmembrane glycoprotein of HIV, rearranges its molecules so that its N-terminal peptides form a trimer of helices that present a fusion peptide to the target cell. Once fusion occurs between the fusion peptide and the target cell membrane, HIV is able to enter and infect the target cell. (Tran) VRC01 binds to CD4’s binding site on gp120, preventing the CD4 receptor from binding to HIV and infecting the cell. (Wu).

spinqualitylabelsall models VRC01 in complex with gp120 Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image Structural Features Similarities to CD4 in complex with gp120. Analysis of VRC01 in complex with gp120 shows that this complex covers 98% of the CD4 binding site. Insert figure Both the heavy chain and light chain of VRC01 contribute to the contact surfaces of the VRC01 gp120 complex. The focus of the binding is on the heavy chain second complementary-determining region. Over 50% of the surface contact involves the heavy chain second complementary-determining region; this is similar to CD4’s interaction with gp120. Two dominant residues, Phe43 and Arg59, are involved in CD4’s binding to gp120. Of these two residues, only the arginine interaction is mimicked by VRC01. This dominant interaction is between Asp368 of gp120 and Arg59 of the CD4 receptor and between Asp368 of gp120 and Arg71 of VRC01. (Zhou) Similarities to other antibodies in complex with gp120. or "jelly-roll" with three other alpha helices (overall making up the ) contain a . This is made from several residues from the N-terminus (Y12, Y20, F22, L25, I27, K31, F33, L61, F69, L71, V81, and V83), and a few from the C-terminus (I226, K230, M259, V261, Y266, and M269). This pocket contains a sixteen-carbon fatty acid positioned in a conformation such that its negatively charged carboxylate group forms salt bridges between K31 of the N-terminal domain, and K230 from the C-terminal domain. The pocket is highly hydrophobic, and has a known volume of 780.9 Angstroms.[1] This pocket contains a ligand: [1] which appears to have a negative effect on virulence when present in vitro. The cis-palmitoleate forms with residues K31 and K230 (for detail, see Figure 1B of: [1]). This unsaturated fatty acid, like other UFAs,[2] tend to inhibit genes under the control of ToxT. Specifically, the cis-palmitoleate (PAM) appears to change ToxT's conformation, and thus lower its ability to bind DNA and form dimers.[1] The presence of UFAs is associated with being in the lumen of the intestine during the bacterial infection. PAM brings K31 and K230 together from either end of the protein, and essentially closes off ToxT. K230 is at the end of helix seven, and binding to K31 causes helix six to be pulled into an unfavorable conformation that deters DNA binding. In lower concentration of fatty acids, ie: after penetrating the intestine's mucus, PAM is in lower concentration. At this point, charge-charge repulsion between K31 and K230 leads to a destabilization of the closed conformation of ToxT. This repulsion prompts the opening of the N and C terminal domains. The freedom of helices six and seven to find a favorable configuration allows DNA binding to occur.[1] MSA 1xtc Other features. VRC01 light chain residues, Tyr28 and Ser30, make contacts with the protein-proximal N-acetyl-glucosamine from the N-linked glycan residue 276 of gp120. While other structures are blocked from binding because glycan shielding, VRC01 takes advantage of the glycan for binding. (Zhou)

HIV Prevention Research

In 2003, Veazey and fellow researchers found that early broadly neutralizing antibodies had microbicide potential by using a monkey cell as the model. The microbicide used on these monkeys consisted of b12, a broadly neutralizing antibody. These monkeys were challenged with SHIV, simian-human immunodeficiency virus, through the vagina. Only three of the twelve monkeys became infected. It was also found that the protection against HIV lasts for up to two hours. (Veazy)These results show that microbicides containing antibodies are effective at preventing HIV in monkeys.

A similar experiment was done in 2012; it used humanized mouse models called RAG-hu mice, which contained human target cells. Results show that seven out of nine mice that were administered the VRC01 antibody and all mice that were given a cocktail containing four broadly neutralizing antibodies as a topical gel were protected against HIV-1. These results showed that broadly neutralizing antibodies could be used as a topical microbicide to prevent vaginal transmission of HIV and that a combination of antibodies can provide better protection against HIV. When the VRC01 antibody and the broadly neutralizing antibody cocktail were administered to the humanized mice via the intravenous route, none of the mice were infected with SHIV. (Veselinovic)

References