title: Epitope mapping and structural analysis of an anti-ErbB2 antibody A21: Molecular basis for tumor inhibitory mechanism.
abstract: Anti-ErbB2 antibodies targeting distinct epitopes can have different biological functions on cancer cells. A21 prepared by surface epitope masking (SEM) method is a tumor-inhibitory anti-ErbB2 monoclonal antibody. Previously we engineered a single chain chimeric antibody chA21 with potential for therapy of ErbB2-overexpressing tumors. Here, we mapped the A21 epitope on ErbB2 extracellular domain (ECD) by screening a combinatorial phage display peptide library, serial subdomain deletion, and mutagenesis scanning. X-ray crystal structure of the A21 scFv fragment at 2.1 A resolution was also determined. A molecular model of Ag-Ab complex was then constructed based on the crystal structures of the A21 scFv and ErbB2 ECD. Some of biological functions of the A21 mAb and its derivative antibodies including their tumor cell growth inhibition and effects on the expression, internalization, and phosphorylation of ErbB2 receptor were also investigated. The results showed that A21 recognized a conformational epitope comprising a large region mostly from ErbB2 extracellular subdomain I with several surface-exposed residues important for the binding affinity. These data provide unique functional properties of A21 that are quite different from two broadly used anti-ErbB2 mAbs, Herceptin and 2C4. It suggested that the A21 epitope may be another valuable target for designing new anti-ErbB2 therapeutics.
authors.affiliation: Lab of Cellular and Molecular Immunology, School of Life Sciences, University of Science and Technology of China, Hefei 230027, People's Republic of China.
authors.forename: Siyi
authors.initials: S
authors.lastname: Hu
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Zhu
authors.forename: Liangwei
authors.initials: L
authors.lastname: Li
authors.forename: Liang
authors.initials: L
authors.lastname: Chang
authors.forename: Weifang
authors.initials: W
authors.lastname: Li
authors.forename: Liansheng
authors.initials: L
authors.lastname: Cheng
authors.forename: Maikun
authors.initials: M
authors.lastname: Teng
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000276:immunology* / Q000494:pharmacology; D000915:Antibody Affinity; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000276:immunology* / Q000494:pharmacology; D001666:Binding Sites, Antibody; D001943:Breast Neoplasms / Q000276:immunology / Q000378:metabolism; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D005260:Female; D006801:Humans; D007128:Immunoglobulin Fragments / Q000276:immunology / Q000378:metabolism; D008958:Models, Molecular; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry* / Q000276:immunology*; D011993:Recombinant Fusion Proteins / Q000276:immunology / Q000378:metabolism; D057127:Single-Chain Antibodies; D013329:Structure-Activity Relationship; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; D000939:Epitopes; D007128:Immunoglobulin Fragments; D018719:Erb-b2 Receptor Tyrosine Kinases; D011993:Recombinant Fusion Proteins; D057127:Single-Chain Antibodies; C479628:monoclonal antibody scFv A21