Antibody recognition of a unique tumor-specific glycopeptide antigen

Abstract

Aberrant glycosylation and the overexpression of certain carbohydrate moieties is a consistent feature of cancers, and tumorassociated oligosaccharides are actively investigated as targets for immunotherapy. One of the most common aberrations in glycosylation patterns is the presentation of a single O-linked N-acetylgalactosamine on a threonine or serine residue known as the "Tn antigen." Whereas the ubiquitous nature of Tn antigens on cancers has made them a natural focus of vaccine research, such carbohydrate moieties are not always tumor-specific and have been observed on embryonic and nonmalignant adult tissue. Here we report the structural basis of binding of a complex of a monoclonal antibody (237mAb) with a truly tumor-specific glycopeptide containing the Tn antigen. In contrast to glycopeptide-specific antibodies in complex with simple peptides, 237mAb does not recognize a conformational epitope induced in the peptide by sugar substitution. Instead, 237mAb uses a pocket coded by germ-line genes to completely envelope the carbohydrate moiety itself while interacting with the peptide moiety in a shallow groove. Thus, 237mAb achieves its striking tumor specificity, with no observed physiological cross-reactivity to the unglycosylated peptide or the free glycan, by a combination of multiple weak but specific interactions to both the peptide and to the glycan portions of the antigen.X-ray crystallography | affinity maturation | crystal structure

BCMab1, A Monoclonal Antibody against Aberrantly Glycosylated Integrin α3β1, Has Potent Antitumor Activity of Bladder Cancer In Vivo

“…Cell adhesion to ECM proteins is strongly modulated by their glycosylation (11). Recent studies showed that aberrant glycosylation has been implicated in tumorigenesis of some tumor types (12,13). Here, we generated a new monoclonal antibody (mAb) BCMab1 against bladder cancer that specifically recognized the aberrantly glycosylated Integrin a3b1 epitope on bladder cancer cells.…”

Improving vaccine efficacy against malignant glioma

“…117 Brooks et al demonstrated that targeting this carbohydrate moiety can result in striking tumor specificity. 118 Further study of unique GBM posttranslational modifications that occur on the surface of the tumor cells may well reveal additional targets with vaccination potential.…”

Deciphering the Non‐Equivalence of Serine and Threonine O‐Glycosylation Points: Implications for Molecular Recognition of the Tn Antigen by an anti‐MUC1 Antibody

“…[8,9] together with the geometries found in X-ray structures for these determinants when bound to some biologicalt argets. [21,[25][26][27][28] Newmanp rojections of Cb-O1 bond are shown. b) Superposition of the Tn antigen moiety a-O-GalNAc-Thr bound to SM3 (in green) and 237-mAb (in yellow; mAb = monoclonal antibody).…”

“…b) Superposition of the Tn antigen moiety a-O-GalNAc-Thr bound to SM3 (in green) and 237-mAb (in yellow; mAb = monoclonal antibody). [21] c) Superposition of the Tn antigen moiety a-O-GalNAcSer bound to SM3 mAb (in green) and to HPA lectin (in yellow). [27] Figure 5.…”

“…[21] In addition, the X-ray structure of am odel anti-MUC1 antibody (SM3) in complex with am ucin is limited to an aked peptide. [22] Moreover,a n NMR study on this peptide and its corresponding GalNAcglycopeptide bound to SM3 led to the hypothesis that the sugar residue fixes the bioactive conformation of the peptide fragment and interacts via the N-acetyl group with the surface of the antibody.…”