Antibody recognition of a unique tumor-specific glycopeptide antigen.
Aberrant glycosylation and the overexpression of certain carbohydrate moieties is a consistent feature of cancers, and tumor-associated 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.
Brooks
Cory L
CL
Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada V8P 3P6.
Schietinger
Andrea
A
Borisova
Svetlana N
SN
Kufer
Peter
P
Okon
Mark
M
Hirama
Tomoko
T
Mackenzie
C Roger
CR
Wang
Lai-Xi
LX
Schreiber
Hans
H
Evans
Stephen V
SV
D000818:Animals; D000911:Antibodies, Monoclonal; D000915:Antibody Affinity; D000918:Antibody Specificity; D000936:Antigen-Antibody Complex / Q000737:chemistry; D015295:Antigens, Tumor-Associated, Carbohydrate / Q000737:chemistry*; D018360:Crystallography, X-Ray; D000939:Epitopes / Q000737:chemistry; D006020:Glycopeptides / Q000737:chemistry / Q000276:immunology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry; D066298:In Vitro Techniques; D051379:Mice; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D055672:Static Electricity; D020349:Surface Plasmon Resonance
D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D015295:Antigens, Tumor-Associated, Carbohydrate; D000939:Epitopes; D006020:Glycopeptides; D007140:Immunoglobulin Fab Fragments; C040286:Tn antigen