The V1V2 Region of HIV-1 gp120 Forms a Five-Stranded Beta Barrel

The V1V2 Region of HIV-1 gp120 Forms a Five-Stranded Beta Barrel

Abstract

The region consisting of the first and second variable regions (V1V2) of gp120 plays vital roles in the functioning of the HIV-1 envelope (Env). V1V2, which harbors multiple glycans and is highly sequence diverse, is located at the Env apex and stabilizes the trimeric gp120 spike on the virion surface. It shields V3 and the coreceptor binding sites in the prefusion state and exposes them upon CD4 binding. Data from the RV144 human HIV-1 vaccine trial suggested that antibody responses targeting the V1V2 region inversely correlated with the risk of infection; thus, understanding the antigenic structure of V1V2 can contribute to vaccine design. We have determined a crystal structure of a V1V2 scaffold molecule (V1V2ZM109-1FD6) in complex with 830A, a human monoclonal antibody that recognizes a V1V2 epitope overlapping the integrin-binding motif in V2. The structure revealed that V1V2 assumes a five-stranded beta barrel structure with the region of the integrin-binding site (amino acids [aa] 179 to 181) included in a “kink” followed by an extra beta strand. The complete barrel structure naturally presents the glycans on its outer surface and packs into its core conserved hydrophobic residues, including the Ile at position 181 which was highly correlated with vaccine efficacy in RV144. The epitope of monoclonal antibody 830A is discontinuous and composed of three segments: (i) Thr175, Tyr177, Leu179, and Asp180 at the kink overlapping the integrin-binding site; (ii) Arg153 and Val154 in V1; and (iii) Ile194 at the C terminus of V2. This report thus provides the atomic details of the immunogenic “V2i epitope.”

IMPORTANCE Data from the RV144 phase III clinical trial suggested that the presence of antibodies to the first and second variable regions (V1V2) of gp120 was associated with the modest protection afforded by the vaccine. V1V2 is a highly variable and immunogenic region of HIV-1 surface glycoprotein gp120, and structural information about this region and its antigenic landscape will be crucial in the design of an effective HIV-1 vaccine. We have determined a crystal structure of V1V2 in complex with human MAb 830A and have shown that MAb 830A recognizes a region overlapping the α4β7 integrin-binding site. We also showed that V1V2 forms a 5-stranded beta barrel, an elegant structure allowing sequence variations in the strand-connecting loops while preserving a conserved core.

Jawahar Raina
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Check us out - ImmunoDx products are in NIBSC!

Check us out - ImmunoDx products are in NIBSC!

ABOUT NIBSC

The National Institute for Biological Standards and Control (NIBSC) plays a major national and international role in assuring the quality of biological medicines through:

  • developing standards and reference materials
  • product control testing
  • carrying out applied research

We play a key role in providing scientific advice and expertise to a large number of organisations, including:

  • manufacturers of biological medicines
  • national regulatory authorities
  • the UK government and European bodies
  • the World Health Organisation
  • UN agencies

Contributions from NIBSC scientists, as members of key decision-making bodies at both European and international level, feed into the development of national and international policies that help to ensure the safety and efficacy of biological medicines.

We serve a broad range of customers and stakeholders in the UK and abroad and have a worldwide reputation for independence, integrity and scientific excellence.

Jawahar Raina
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Antibody detection by agglutination–PCR (ADAP) enables early diagnosis of HIV infection by oral fluid analysis

Antibody detection by agglutination–PCR (ADAP) enables early diagnosis of HIV infection by oral fluid analysis

There is a substantial public health interest in identifying HIV-infected individuals through population-based screening. Oral fluid (OF) is easier to collect than blood and therefore ideal for such screening efforts. Unfortunately, OF has a very low concentration of anti-HIV antibodies (markers of HIV infection), which current assays cannot detect during the early stage of this disease. Here we report an assay for anti-HIV antibodies in OF that is up to 10,000 times more sensitive than current alternatives. This assay, called Antibody Detection by Agglutination–PCR (ADAP), could be broadly deployed to screen at-risk populations using OF in many settings, including those where cold chain shipping is not available (low-resource settings) and where needles are inconvenient (pediatrics) or unsafe (prisons).
Jawahar Raina
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ImmunoDx HIV-1 p24 Monoclonal Antibody gets Recognition (1103)

ImmunoDx HIV-1 p24 Monoclonal Antibody gets Recognition (1103)

The prevailing method to assess HIV-1 replication and infectivity is to measure the production of p24 Gag protein by enzyme-linked immunosorbent assay (ELISA). Since fluorescent bead-based technologies offer a broader dynamic range and higher sensitivity, this study describes a p24 capture Luminex assay capable of detecting HIV-1 subtypes A, B, C, D, circulating recombinant forms (CRF) CRF01_AE and CRF02_AG, which together are responsible for over 90% of HIV-1 infections worldwide. The success of the assay lies in the identification and selection of a cross-reactive capture antibody (clone 183-H12-5C). Fifty-six isolates that belonged to six HIV-1 subtypes and CRFs were successfully detected with p-values below 0.021; limits of detection ranging from 3.7 to 3×104 pg/ml. The intra- and inter-assay variation gave coefficient of variations below 6 and 14%, respectively. The 183-bead Luminex assay also displayed higher sensitivity of 91% and 98% compared to commercial p24 ELISA and a previously described Luminex assay. The p24 concentrations measured by the 183-bead Luminex assay showed a significant correlation (R = 0.92, p<0.0001) with the data obtained from quantitative real time PCR.

This newly developed p24 assay leverages the advantages of the Luminex platform, which include smaller sample volume and simultaneous detection of up to 500 analytes in a single sample, and delivers a valuable tool for the field.

Keywords: HIV-1, p24, detection, multi-subtype, multiplex assay
Jawahar Raina
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Gene cloning system

Launch of HEK293 product line!

ImmunoDX has developed a double-cassette gene cloning system in human HEK293 cells that allows the determination of stable gene expression of any cloned genes in 3 days post  transfection and expression-selection in a 5 minute test- lateral flow diagnostics. Most HEK293 derived HIV-1 envelope M, T, M/T tropic virus envelope gene products may be ordered on our web site. 

Jawahar Raina
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