Computational model of the full-length TSH receptor
Abstract:
The receptor for thyroid stimulating hormone (TSHR), a GPCR,
is of particular interest as the primary antigen in autoimmune hyperthyroidism (Graves' disease)
caused by stimulating TSHR antibodies.
To date, only one domain of the extracellular region of the TSHR has been crystallized.
We have run a 1000ns Molecular Dynamic simulation on a model of the entire TSHR
generated by merging the extracellular region of the receptor, obtained using
artificial intelligence, with our recent homology model of the transmembrane domain,
embedded it in a lipid membrane solvated it with water and counterions.
The simulations showed that the structure of the transmembrane and leucine-rich domains
were remarkably constant while the linking region (LR), known more commonly as
the "hinge region", showed significant flexibility, forming several
transient secondary structural elements.
Furthermore, the relative orientation of the leucine-rich domain with the rest of the receptor
was also seen to be variable.
These data suggest that this linker region is an intrinsically disordered protein (IDP).
Furthermore, preliminary data simulating the full TSHR model complexed with its ligand (TSH)
showed that (a) there is a strong affinity between the linker region and TSH ligand and
(b) the association of the linker region and the TSH ligand reduces the
structural fluctuations in the linker region.
This full-length model illustrates the importance of the linker region
in responding to ligand binding and lays the foundation for studies of
pathologic TSHR autoantibodies complexed with the TSHR
to give further insight into their interaction with the flexible linker region.