4QT5

Crystal Structure of 3BD10: A Monoclonal Antibody against the TSH Receptor

Summary for 4QT5

• Entry DOI: 10.2210/pdb4qt5/pdb
• Descriptor: 3BD10 mouse monoclonal antibody, light chain, 3BD10 mouse monoclonal antibody, heavy chain (3 entities in total)
• Functional Keywords: graves disease, antibody, tsh receptor, thyroid, immune system
• Biological source: Mus musculus; More
• Total number of polymer chains: 4
• Total formula weight: 93494.09

Authors

Hubbard, P.A.,Chen, C.R.,McLachlan, S.M.,Rapoport, B.,Murali, R. (deposition date: 2014-07-07, release date: 2015-04-01, Last modification date: 2024-10-09)

Primary citation

Chen, C.R.,Hubbard, P.A.,Salazar, L.M.,McLachlan, S.M.,Murali, R.,Rapoport, B.
Crystal structure of a TSH receptor monoclonal antibody: insight into Graves' disease pathogenesis.
Mol.Endocrinol., 29:99-107, 2015

PubMed Abstract: The TSH receptor (TSHR) A-subunit is more effective than the holoreceptor in inducing thyroid-stimulating antibodies (TSAb) that cause Graves' disease. A puzzling phenomenon is that 2 recombinant, eukaryotic forms of A-subunits (residues 22-289), termed active and inactive, are recognized mutually exclusively by pathogenic TSAb and mouse monoclonal antibody 3BD10, respectively. Understanding the structural difference between these TSHR A-subunit forms could provide insight into Graves' disease pathogenesis. The 3-dimensional structure of the active A-subunit (in complex with a human TSAb Fab, M22) is known, but the structural difference with inactive A-subunits is unknown. We solved the 3BD10 Fab 3-dimensional crystal structure. Guided by prior knowledge of a portion of its epitope, 3BD10 docked in silico with the known active TSHR-289 monomeric structure. Because both TSAb and 3BD10 recognize the active TSHR A-subunit monomer, this form of the molecule can be excluded as the basis for the active-inactive dichotomy, suggesting, instead a role for A-subunit quaternary structure. Indeed, in silico analysis revealed that M22, but not 3BD10, bound to a TSHR-289 trimer. In contrast, 3BD10, but not M22, bound to a TSHR-289 dimer. The validity of these models is supported experimentally by the temperature-dependent balance between active and inactive TSHR-289. In summary, we provide evidence for a structural basis to explain the conformational heterogeneity of TSHR A-subunits (TSHR-289). The pathophysiologic importance of these findings is that affinity maturation of pathogenic TSAb in Graves' disease is likely to involve a trimer of the shed TSHR A-subunit.

PubMed: 25419797
DOI: 10.1210/me.2014-1257

Experimental method

X-RAY DIFFRACTION (2.5 Å)