Model-building study of the combining sites of two antibodies to alpha (1----6)dextran.

Padlan, Eduardo A.; Kabat, Elvin A.

doi:10.1073/pnas.85.18.6885

Cited by 46 publications

(36 citation statements)

References 30 publications

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“…This may be explained, in part, by the Ab structures that bind them. In several instances, peptide-and CHO-reactive mAbs have been shown to possess groove-like binding sites (28)(29)(30)(31). Work by Vargas-Madrazo et al (32) suggests that the majority of anti-CHO Abs use a limited subset of V genes, indicating that this class of Abs uses a restricted structural repertoire.…”

Section: Discussionmentioning

confidence: 99%

Exploring the basis of peptide–carbohydrate crossreactivity: Evidence for discrimination by peptides between closely related anti-carbohydrate antibodies

Harris

Craig

Mehroke

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

120

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To investigate the molecular basis of antigenic mimicry by peptides, we studied a panel of closely related mAbs directed against the cell-wall polysaccharide of group A Streptococcus. These antibodies have restricted V-gene usage, indicating a shared mechanism of binding to a single epitope. Epitope mapping studies using synthetic fragments of the cell-wall polysaccharide supported this conclusion. All of the mAbs isolated crossreactive peptides from a panel of phagedisplayed libraries, and competition studies indicated that many of the peptides bind at or near the carbohydrate binding site. Surprisingly, the peptides isolated by each mAb fell into distinct consensus-sequence groups that discriminated between the mAbs, and in general, the peptides bound only to the mAbs used for their isolation. Similar results were obtained with polyclonal antibodies directed against synthetic oligosaccharide fragments of the streptococcal cell-wall polysaccharide. Thus, the peptides appear to be specific for their isolating antibodies and are not recognized by the same mechanism as their carbohydrate counterparts.Carbohydrates (CHOs) have proven to be valuable tools in demonstrating immunologic mimicry. Anti-idiotypic antibodies (Abs) directed against the V domains of anti-CHO Abs can, in some instances, elicit CHO-binding Ab responses when used themselves as immunogens (e.g., refs. 1-4). This has been attributed to chemical similarity (known as the ''internal image'') between an anti-idiotypic Ab and the corresponding CHO antigen (1). Likewise, crossreactive peptides have been identified for several anti-CHO mAbs (4-7). In one case, the peptide was shown to elicit Abs having the same idiotype as the cognate, anti-CHO mAb (5), and in another to elicit a CHObinding response (4).The work described here addresses the molecular basis of crossreactivity between CHO and protein antigens with Abs. Our goal was to determine if the crossreactive peptides recognized by anti-CHO Abs would bind by the same mechanism as the corresponding epitope on the CHO target; if so, the basis of crossreactivity would be structural mimicry. We assembled a panel of five closely related mAbs against the cell-wall polysaccharide (CWPS) of group A Streptococcus (GAS) and showed by oligosaccharide mapping studies that they indeed bind a similar, if not identical, epitope. Each of four anti-GAS CWPS mAbs and three polyclonal Abs (PCAbs) against synthetic oligosaccharide fragments of the GAS CWPS isolated peptides bearing unique, chemically distinct consensus sequences. Moreover, representative peptides from each consensus group were functionally specific, because they usually bound only to their isolating Ab. Thus, these Abs were more restricted in their peptide reactivity than in their CHO recognition. We conclude that the predominating basis of peptide recognition by anti-CHO Abs differs between Abs, with true CHO mimics being relatively rare. We propose that the antigenic mimicry observed for CHO-crossreactive peptides is determined mainly by the ...

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Section: Discussionmentioning

confidence: 99%

Exploring the basis of peptide–carbohydrate crossreactivity: Evidence for discrimination by peptides between closely related anti-carbohydrate antibodies

Harris

Craig

Mehroke

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

120

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“…It was concluded that small epitopes generally include the nonreducing terminal residue, whereas larger epitopes are located along the length of the polysaccharide chain (17). It was further suggested that small epitopes bind to cavity-type antigen-binding-site topologies, whereas larger internal epitopes are recognized by groove-type topologies (18). Although few bacterial oligosaccharideantibody crystal structures have been reported to date (19)(20)(21), these early estimates of epitope size and nature, and their relationship to binding-site topology, are largely concordant with current structural data.…”

Section: Discussionmentioning

confidence: 99%

Structures of synthetic O-antigen fragments from serotype 2aShigella flexneriin complex with a protective monoclonal antibody

Normand

Saul

Phalipon

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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The anti-LPS IgG mAb F22-4, raised against Shigella flexneri serotype 2a bacteria, protects against homologous, but not heterologous, challenge in an experimental animal model. We report the crystal structures of complexes formed between Fab F22-4 and two synthetic oligosaccharides, a decasaccharide and a pentadecasaccharide that were previously shown to be both immunogenic and antigenic mimics of the S. flexneri serotype 2a O-antigen. F22-4 binds to an epitope contained within two consecutive 2a serotype pentasaccharide repeat units (RU). Six sugar residues from a contiguous nine-residue segment make direct contacts with the antibody, including the nonreducing rhamnose and both branching glucosyl residues from the two RUs. The glucosyl residue, whose position of attachment to the tetrasaccharide backbone of the RU defines the serotype 2a O-antigen, is critical for recognition by F22-4. Although the complete decasaccharide is visible in the electron density maps, the last four pentadecasaccharide residues from the reducing end, which do not contact the antibody, could not be traced. Although considerable mobility in the free oligosaccharides can thus be expected, the conformational similarity between the individual RUs, both within and between the two complexes, suggests that short-range transient ordering to a helical conformation might occur in solution. Although the observed epitope includes the terminal nonreducing residue, binding to internal epitopes within the polysaccharide chain is not precluded. Our results have implications for vaccine development because they suggest that a minimum of two RUs of synthetic serotype 2a oligosaccharide is required for optimal mimicry of O-Ag epitopes.antibody complex ͉ carbohydrate ͉ crystal structure ͉ polyliposaccharide ͉ shigellosis S higellosis (1), or bacillary dysentery, causes significant morbidity and mortality worldwide, particularly among young children (2). The disease arises from colonization and subsequent destruction of the colonic mucosa by the Gram-negative enteroinvasive bacteria Shigella. Immune protection induced by natural infection derives from antibodies directed against the bacterial surface antigen lipopolysaccharide (LPS) (3). Moreover, protection shows a serotype specificity that is determined by the repeat unit (RU) structure of the O-antigen (O-Ag), the polysaccharide moiety of LPS (4). In the species Shigella flexneri, which is responsible for endemic infections in developing countries, the serotype is defined by glucosyl and O-acetyl modifications added to the basic tri-rhamnose-N-acetyl-glucosamine tetrasaccharide (designated ABCD) of the O-Ag backbone (5). (Serotype 6 is an exception.) Of the 14 S. flexneri serotypes identified to date, the 2a serotype is the most prevalent in developing countries (2). The serotype 2a RU is characterized by a branching glucose (residue E) linked to the third rhamnose (residue C) to form the motif AB(E)CD (Fig. 1).The induction of protective immunity by natural infection with Shigella suggests that an effe...

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“…Cavity-like and groove-type sites for anti-carbohydrate antibodies, including antibodies to LPS OAg from Shigella flexneri, Vibrio cholerae, and Brucella abortus, were supported by immunochemical, computer modeling, and x-ray crystallographic studies. (41)(42)(43)(44)(45)(46)(47)(48)(49)(50) These showed a maximum of five sugar residues accommodated by cavity-type sites and six to eight sugar residues accommodated by groove-type sites. In the current study, FB11 may have a cavity-type site and the other three anti-Ft OAg MAbs likely have groove-type sites.…”

Section: Biacore Analysis Confirms Higher Avidity Of End-binding Mabmentioning

confidence: 99%

Characterization of Monoclonal Antibodies to Terminal and Internal O-Antigen Epitopes ofFrancisella tularensisLipopolysaccharide

Roche

Hui

et al. 2011

Hybridoma

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The lipopolysaccharide (LPS) of Francisella tularensis (Ft), the Gram negative bacterium that causes tularemia, has been shown to be a main protective antigen in mice and humans; we have previously demonstrated that murine anti-Ft LPS IgG2a monoclonal antibodies (MAbs) can protect mice against otherwise lethal intranasal infection with the Ft live vaccine strain (LVS). Here we show that four IgG2a anti-LPS MAbs are specific for the O-polysaccharide (O-antigen [OAg]) of Ft LPS. But whereas three of the MAbs bind to immunodominant repeating internal epitopes, one binds to a unique terminal epitope of Ft OAg. This was deduced from its even binding to both long and short chains of the LPS ladder in Western blots, its rapid decrease in ELISA binding to decreasing solid-phase LPS concentrations, its inability to compete for LPS binding with a representative of the other three MAbs, and its inability to immunoprecipitate OAg despite its superior agglutination titer. Biacore analysis showed the end-binding MAb to have higher bivalent avidity for Ft OAg than the internal-binding MAbs and provided an immunogenicity explanation for the predominance of internal-binding anti-Ft OAg MAbs. These findings demonstrate that non-overlapping epitopes can be targeted by antibodies to Ft OAg, which may inform the design of vaccines and immunotherapies against tularemia.

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Model-building study of the combining sites of two antibodies to alpha (1----6)dextran.

Cited by 46 publications

References 30 publications

Exploring the basis of peptide–carbohydrate crossreactivity: Evidence for discrimination by peptides between closely related anti-carbohydrate antibodies

Exploring the basis of peptide–carbohydrate crossreactivity: Evidence for discrimination by peptides between closely related anti-carbohydrate antibodies

Structures of synthetic O-antigen fragments from serotype 2aShigella flexneriin complex with a protective monoclonal antibody

Characterization of Monoclonal Antibodies to Terminal and Internal O-Antigen Epitopes ofFrancisella tularensisLipopolysaccharide

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