Crystal structure of the TSH receptor in complex with a thyroid-stimulating autoantibody.
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.
Sanders
Jane
J
FIRS Laboratories, RSR Ltd., Llanishen, Cardiff, United Kingdom.
Chirgadze
Dimitri Y
DY
Sanders
Paul
P
Baker
Stuart
S
Sullivan
Andrew
A
Bhardwaja
Anshu
A
Bolton
Jane
J
Reeve
Magnus
M
Nakatake
Nobuhiro
N
Evans
Michele
M
Richards
Tonya
T
Powell
Michael
M
Miguel
Ricardo Núñez
RN
Blundell
Tom L
TL
Furmaniak
Jadwiga
J
Smith
Bernard Rees
BR
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
D007140:Immunoglobulin Fab Fragments; D018828:Immunoglobulins, Thyroid-Stimulating; D011962:Receptors, FSH; D011989:Receptors, Thyrotropin; D005640:Follicle Stimulating Hormone