title: Crystal structure of the TSH receptor in complex with a thyroid-stimulating autoantibody.
abstract: OBJECTIVE
  To analyze interactions between the thyroid-stimulating hormone receptor (TSHR) and a thyroid-stimulating human monoclonal autoantibody (M22) at the molecular level.
  
  
  METHODS
  A complex of part of the TSHR extracellular domain (amino acids 1-260; TSHR260) bound to M22 Fab was prepared and purified. Crystals suitable for X-ray diffraction analysis were obtained and the structure solved at 2.55 A resolution.
  
  
  RESULTS
  TSHR260 comprises of a curved helical tube and M22 Fab clasps its concave surface at 90 degrees to the tube length axis. The interface buried in the complex is large (2,500 A(2)) and an extensive network of ionic, polar, and hydrophobic bonding is involved in the interaction. There is virtually no movement in the atoms of M22 residues on the binding interface compared to unbound M22 consistent with "lock and key" binding. Mutation of residues showing strong interactions in the structure influenced M22 activity, indicating that the binding detail observed in the complex reflects interactions of M22 with intact, functionally active TSHR. The receptor-binding arrangements of the autoantibody are very similar to those reported for follicle-stimulating hormone (FSH) binding to the FSH receptor (amino acids 1-268) and consequently to those of TSH itself.
  
  
  CONCLUSIONS
  It is remarkable that the thyroid-stimulating autoantibody shows almost identical receptor-binding features to TSH although the structures and origins of these two ligands are very different. Furthermore, our structure of the TSHR and its complex with M22 provide foundations for developing new strategies to understand and control both glycoprotein hormone receptor activation and the autoimmune response to the TSHR.
authors.affiliation: FIRS Laboratories, RSR Ltd., Llanishen, Cardiff, United Kingdom.
authors.forename: Jane
authors.initials: J
authors.lastname: Sanders
authors.forename: Dimitri Y
authors.initials: DY
authors.lastname: Chirgadze
authors.forename: Paul
authors.initials: P
authors.lastname: Sanders
authors.forename: Stuart
authors.initials: S
authors.lastname: Baker
authors.forename: Andrew
authors.initials: A
authors.lastname: Sullivan
authors.forename: Anshu
authors.initials: A
authors.lastname: Bhardwaja
authors.forename: Jane
authors.initials: J
authors.lastname: Bolton
authors.forename: Magnus
authors.initials: M
authors.lastname: Reeve
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Nakatake
authors.forename: Michele
authors.initials: M
authors.lastname: Evans
authors.forename: Tonya
authors.initials: T
authors.lastname: Richards
authors.forename: Michael
authors.initials: M
authors.lastname: Powell
authors.forename: Ricardo Núñez
authors.initials: RN
authors.lastname: Miguel
authors.forename: Tom L
authors.initials: TL
authors.lastname: Blundell
authors.forename: Jadwiga
authors.initials: J
authors.lastname: Furmaniak
authors.forename: Bernard Rees
authors.initials: BR
authors.lastname: Smith
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003460:Crystallization; D005640:Follicle Stimulating Hormone / Q000737:chemistry; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry; D018828:Immunoglobulins, Thyroid-Stimulating / Q000737:chemistry*; D008969:Molecular Sequence Data; D009154:Mutation; D011962:Receptors, FSH / Q000737:chemistry; D011989:Receptors, Thyrotropin / Q000737:chemistry* / Q000235:genetics; D014961:X-Ray Diffraction
chemical_list: D007140:Immunoglobulin Fab Fragments; D018828:Immunoglobulins, Thyroid-Stimulating; D011962:Receptors, FSH; D011989:Receptors, Thyrotropin; D005640:Follicle Stimulating Hormone