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The broadly neutralizing anti-human immunodeficiency virus type 1 antibody 2G12 recognizes a cluster of alpha1-->2 mannose residues on the outer face of gp120.

ABSTRACT: 2G12 is a broadly neutralizing human monoclonal antibody against human immunodeficiency virus type-1 (HIV-1) that has previously been shown to bind to a carbohydrate-dependent epitope on gp120. Here, site-directed mutagenesis and carbohydrate analysis were used to define further the 2G12 epitope. Extensive alanine scanning mutagenesis showed that elimination of the N-linked carbohydrate attachment sequences associated with residues N295, N332, N339, N386, and N392 by N-->A substitution produced significant decreases in 2G12 binding affinity to gp120(JR-CSF). Further mutagenesis suggested that the glycans at N339 and N386 were not critical for 2G12 binding to gp120(JR-CSF). Comparison of the sequences of isolates neutralized by 2G12 was also consistent with a lesser role for glycans attached at these positions. The mutagenesis studies provided no convincing evidence for the involvement of gp120 amino acid side chains in 2G12 binding. Antibody binding was inhibited when gp120 was treated with Aspergillus saitoi mannosidase, Jack Bean mannosidase, or endoglycosidase H, indicating that Man(alpha)1-->2Man-linked sugars of oligomannose glycans on gp120 are required for 2G12 binding. Consistent with this finding, the binding of 2G12 to gp120 could be inhibited by monomeric mannose but not by galactose, glucose, or N-acetylglucosamine. The inability of 2G12 to bind to gp120 produced in the presence of the glucose analogue N-butyl-deoxynojirimycin similarly implicated Man(alpha)1-->2Man-linked sugars in 2G12 binding. Competition experiments between 2G12 and the lectin cyanovirin for binding to gp120 showed that 2G12 only interacts with a subset of available Man(alpha)1-->2Man-linked sugars. Consideration of all the data, together with inspection of a molecular model of gp120, suggests that the most likely epitope for 2G12 is formed from mannose residues contributed by the glycans attached to N295 and N332, with the other glycans playing an indirect role in maintaining epitope conformation.

SUBMITTER: Scanlan CN

PROVIDER: S-EPMC136327 | biostudies-literature | 2002 Jul

REPOSITORIES: biostudies-literature

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The broadly neutralizing anti-human immunodeficiency virus type 1 antibody 2G12 recognizes a cluster of alpha1-->2 mannose residues on the outer face of gp120.

Scanlan Christopher N CN Pantophlet Ralph R Wormald Mark R MR Ollmann Saphire Erica E Stanfield Robyn R Wilson Ian A IA Katinger Hermann H Dwek Raymond A RA Rudd Pauline M PM Burton Dennis R DR

Journal of virology 20020701 14

2G12 is a broadly neutralizing human monoclonal antibody against human immunodeficiency virus type-1 (HIV-1) that has previously been shown to bind to a carbohydrate-dependent epitope on gp120. Here, site-directed mutagenesis and carbohydrate analysis were used to define further the 2G12 epitope. Extensive alanine scanning mutagenesis showed that elimination of the N-linked carbohydrate attachment sequences associated with residues N295, N332, N339, N386, and N392 by N-->A substitution produced ...[more]

PMID: 12072529

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Project description:Chikungunya virus (CHIKV) is a reemerging alphavirus that causes a debilitating arthritic disease and infects millions of people and for which no specific treatment is available. Like many alphaviruses, the structural targets on CHIKV that elicit a protective humoral immune response in humans are poorly defined. Here we used phage display against virus-like particles (VLPs) to isolate seven human monoclonal antibodies (MAbs) against the CHIKV envelope glycoproteins E2 and E1. One MAb, IM-CKV063, was highly neutralizing (50% inhibitory concentration, 7.4 ng/ml), demonstrated high-affinity binding (320 pM), and was capable of therapeutic and prophylactic protection in multiple animal models up to 24 h postexposure. Epitope mapping using a comprehensive shotgun mutagenesis library of 910 mutants with E2/E1 alanine mutations demonstrated that IM-CKV063 binds to an intersubunit conformational epitope on domain A, a functionally important region of E2. MAbs against the highly conserved fusion loop have not previously been reported but were also isolated in our studies. Fusion loop MAbs were broadly cross-reactive against diverse alphaviruses but were nonneutralizing. Fusion loop MAb reactivity was affected by temperature and reactivity conditions, suggesting that the fusion loop is hidden in infectious virions. Visualization of the binding sites of 15 different MAbs on the structure of E2/E1 revealed that all epitopes are located at the membrane-distal region of the E2/E1 spike. Interestingly, epitopes on the exposed topmost and outer surfaces of the E2/E1 trimer structure were neutralizing, whereas epitopes facing the interior of the trimer were not, providing a rationale for vaccine design and therapeutic MAb development using the intact CHIKV E2/E1 trimer.CHIKV is the most important alphavirus affecting humans, resulting in a chronic arthritic condition that can persist for months or years. In recent years, millions of people have been infected globally, and the spread of CHIKV to the Americas is now beginning, with over 100,000 cases occurring in the Caribbean within 6 months of its arrival. Our study reports on seven human MAbs against the CHIKV envelope, including a highly protective MAb and rarely isolated fusion loop MAbs. Epitope mapping of these MAbs demonstrates how some E2/E1 epitopes are exposed or hidden from the human immune system and suggests a structural mechanism by which these MAbs protect (or fail to protect) against CHIKV infection. Our results suggest that the membrane-distal end of CHIKV E2/E1 is the primary target for the humoral immune response to CHIKV, and antibodies targeting the exposed topmost and outer surfaces of the E2/E1 trimer determine the neutralizing efficacy of this response.

Dataset Information

The broadly neutralizing anti-human immunodeficiency virus type 1 antibody 2G12 recognizes a cluster of alpha1-->2 mannose residues on the outer face of gp120.

Publications

The broadly neutralizing anti-human immunodeficiency virus type 1 antibody 2G12 recognizes a cluster of alpha1-->2 mannose residues on the outer face of gp120.

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