Epitope

An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The part of an antibody that binds to the epitope is called a paratope. Although epitopes are usually non-self proteins, sequences derived from the host that can be recognized (as in the case of autoimmune diseases) are also epitopes. The epitopes of protein antigens are divided into two categories, conformational epitopes and linear epitopes, based on their structure and interaction with the paratope. Conformational and linear epitopes interact with the paratope based on the 3-D conformation adopted by the epitope, which is determined by the surface features of the involved epitope residues and the shape or tertiary structure of other segments of the antigen. A conformational epitope is formed by the 3-D conformation adopted by the interaction of discontiguous amino acid residues. In contrast, a linear epitope is for

Autoreactive epitopes defined by diabets-associated human monoclonal-antibodies are localited in the middle and C-Terminal domains of the smaller form of glutamate-decarboxylase

Steinunn Baekkeskov Hanahan

The gamma-aminobutyrate-synthesizing enzyme glutamate decarboxylase (GAD; L-glutamate 1-carboxy-lyase, EC 4.1.1.15) is a major target of autoantibodies associated with both early and late stages of pancreatic beta-cell destruction and development of type 1 diabetes. We have used five monoclonal anti-islet-cell antibodies (MICAs 1,2,3,4, and 6) derived from a newly diagnosed diabetic patient to probe the autoimmune epitopes in the enzyme. All the MICAs specifically recognized the smaller GAD protein, GAD65, and did not recognize the nonallelic GAD67 protein. A series of N-terminal, C-terminal, and internal deletion mutants, as well as protein footprinting, were used to identify the target regions in GAD65. Immunoprecipitation revealed two major native epitope areas in the GAD65 molecule. The first, defined by MICAs 1 and 3, is destroyed by deleting 41 amino acids at the C terminus but is also dependent on intact amino acids 244-295. This epitope (or epitopes) may span both middle and C-terminal domains of the protein. The second conformational epitope region, defined by MICAs 4 and 6, is dependent on intact amino acids 245-295 but is not affected by deletion of 110 amino acids at the C terminus and is therefore confined to domain(s) in the middle of the molecule. MICA 2 recognizes a linear epitope close to the C terminus. Thus, the N-terminal domain of GAD65, which differs most significantly from GAD67, does not harbor the MICA epitopes. Rather subtle amino acid differences in the middle and C-terminal domains define the GAD65-specific autoimmune epitopes. Analysis of sera from 10 type 1 diabetic patients suggests that MICAs 1, 3, 4, and 6 represent a common epitope recognition in this disease, whereas the MICA 2 epitope is rare. Furthermore, autoantibodies in some sera are restricted to the MICA 1/3 epitope, suggesting that this epitope may represent a single dominant epitope in the early phases of beta-cell autoimmunity.

National Academy of Sciences1993

High-resolution autoreactive epitope mapping and structural modeling of the 65 kDa form of human glutamic acid decarboxylase

Steinunn Baekkeskov Hanahan

The smaller isoform of the GABA-synthesizing enzyme, glutamic acid decarboxylase 65 (GAD65), is unusually susceptible to becoming a target of autoimmunity affecting its major sites of expression, GABA-ergic neurons and pancreatic β-cells. In contrast, a highly homologous isoform, GAD67, is not an autoantigen. We used homolog-scanning mutagenesis to identify GAD65-specific amino acid residues which form autoreactive B-cell epitopes in this molecule. Detailed mapping of 13 conformational epitopes, recognized by human monoclonal antibodies derived from patients, together with two and three-dimensional structure prediction led to a model of the GAD65 dimer. GAD65 has structural similarities to ornithine decarboxylase in the pyridoxal-5′-phosphate-binding middle domain (residues 201-460) and to dialkylglycine decarboxylase in the C-terminal domain (residues 461-585). Six distinct conformational and one linear epitopes cluster on the hydrophilic face of three amphipathic α-helices in exons 14-16 in the C-terminal domain. Two of those epitopes also require amino acids in exon 4 in the N-terminal domain. Two distinct epitopes reside entirely in the N-terminal domain. In the middle domain, four distinct conformational epitopes cluster on a charged patch formed by amino acids from three α-helices away from the active site, and a fifth epitope resides at the back of the pyridoxal 5′-phosphate binding site and involves amino acid residues in exons 6 and 11-12. The epitopes localize to multiple hydrophilic patches, several of which also harbor DR∗0401-restricted T-cell epitopes, and cover most of the surface of the protein. The results reveal a remarkable spectrum of human autoreactivity to GAD65, targeting almost the entire surface, and suggest that native folded GAD65 is the immunogen for autoreactive B-cells.

Elsevier1999

High-resolution autoreactive epitope mapping and structural modeling of the 65 kDa form of human glutamic acid decarboxylase

Steinunn Baekkeskov Hanahan

Elsevier1999

Autoreactive epitopes defined by diabets-associated human monoclonal-antibodies are localited in the middle and C-Terminal domains of the smaller form of glutamate-decarboxylase

Steinunn Baekkeskov Hanahan

National Academy of Sciences1993

Epitope tagging of the murine serotonin receptor 5-HT3 for structural analysis and surface immobilization.

Autoreactive epitopes defined by diabets-associated human monoclonal-antibodies are localited in the middle and C-Terminal domains of the smaller form of glutamate-decarboxylase

High-resolution autoreactive epitope mapping and structural modeling of the 65 kDa form of human glutamic acid decarboxylase

High-resolution autoreactive epitope mapping and structural modeling of the 65 kDa form of human glutamic acid decarboxylase

Epitope tagging of the murine serotonin receptor 5-HT3 for structural analysis and surface immobilization.

Autoreactive epitopes defined by diabets-associated human monoclonal-antibodies are localited in the middle and C-Terminal domains of the smaller form of glutamate-decarboxylase