Sandbox Reserved 1779: Difference between revisions

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The ECD of TSHR is anchored to the membrane through seven transmembrane helices (7TMD), characteristic of GPCRs. Conformational changes in the 7TMD activate intracellular G-protein signaling<ref name= "Keinau et al.">Kleinau, G., Worth, C. L., Kreuchwig, A., Biebermann, H., Marcinkowski, P., Scheerer, P., & Krause, G. (2017). Structural–functional features of the thyrotropin receptor: A class A G-protein-coupled receptor at work. Frontiers in Endocrinology, 8. https://doi.org/10.3389/fendo.2017.00086</ref>. Once TSH binds, changes to the p10 peptide are transmitted to the 7TMD. Specifically, hinge helix rotation causes displacement of the p10 peptide that allows the <scene name='95/952709/Helix_7_of_7tmd/2'>seventh transmembrane helix (TM7)</scene> to migrate towards the center of the 7TMD to increase van Der Waals contacts. Additionally, K660 of TM7 forms a stabilizing <scene name='95/952709/Helix_7_and__p10_interaction/6'>ionic interaction</scene> with E409 of the p10 region. Hinge helix movement also rearranges Y279 relative to I486 on the neighboring <scene name='95/952709/Hinge_helix_ecl1/3'>extracellular loop 1 (ECL1) helix</scene>, which links two transmembrane helices and is located extracellularly. Substitution of these residues leads to substantial shifts in the activation of the thyrotropin receptor. Structurally guided mutagenic studies have shown that replacing isoleucine with a more sizeable phenylalanine decreases TSH signaling potency<ref name="Faust et al.">Faust, B., Billesbølle, C.B., Suomivuori, CM. et al. Autoantibody mimicry of hormone action at the thyrotropin receptor. Nature 609, 846–853 (2022). https://doi.org/10.1038/s41586-022-</ref><ref name="Vlaeminck-Guillem et al.">Virginie Vlaeminck-Guillem, Su-Chin Ho, Patrice Rodien, Gilbert Vassart, Sabine Costagliola, Activation of the cAMP Pathway by the TSH Receptor Involves Switching of the Ectodomain from a Tethered Inverse Agonist to an Agonist, Molecular Endocrinology, Volume 16, Issue 4, 1 April 2002, Pages 736–746, https://doi.org/10.1210/mend.16.4.0816</ref>.The sixth transmembrane helix of TSHR moves outward from the center of the 7TMD to facilitate α-helix 5 of the α-subunit of the G protein (Gα)<ref name="Faust et al.">Faust, B., Billesbølle, C.B., Suomivuori, CM. et al. Autoantibody mimicry of hormone action at the thyrotropin receptor. Nature 609, 846–853 (2022). https://doi.org/10.1038/s41586-022-</ref><ref name="Goricanec et al.">Goricanec, D., Stehle, R., Egloff, P., Grigoriu, S., Plückthun, A., Wagner, G., & Hagn, F. (2016). Conformational dynamics of a G-protein α subunit is tightly regulated by nucleotide binding. Proceedings of the National Academy of Sciences, 113(26). https://doi.org/10.1073/pnas.1604125113 </ref>. Gα is activated for intracellular signaling when GDP is exchanged for GTP and dissociates from the γ- and β-subunits of the G-protein (Gγ and Gβ) to bind with other target proteins. Activation of the Gα is caused by conformational shifts in the 7TMD and three intracellular loops which directly interact with the G-protein<ref name= "Keinau et al.">Kleinau, G., Worth, C. L., Kreuchwig, A., Biebermann, H., Marcinkowski, P., Scheerer, P., & Krause, G. (2017). Structural–functional features of the thyrotropin receptor: A class A G-protein-coupled receptor at work. Frontiers in Endocrinology, 8. https://doi.org/10.3389/fendo.2017.00086</ref>. Conformational shifts in transmembrane helices are the mechanism of changing interactions of the G-protein with the receptor. Activation of the G-protein is caused by these conformational shifts.

~~=== Leucine Rich Repeats ===~~

The Leucine Rich Repeat Domain (LRRD) is part of the <scene name='95/952708/Tshr_chainr_ecd/1'>ECD</scene> of TSHR and contains <scene name='95/952707/Lrr/3'>10-11 Leucine Rich Repeats</scene>. A unique feature of this region is that it is composed entirely of β-pleated sheets. These β-pleated sheets of the LRRD provides a concave binding surface for TSH, including <scene name='95/952707/Interactions_with_thyrotropin/2'>K209 and K58</scene> <ref name="Duan et al.">PMID: 35940204</ref>. These interact with <scene name='95/952707/Interactions_with_thyrotropin/2'>N91 and E98</scene> in the seatbelt region of TSH forming a salt bridge and initiating the conformational change by pulling on the hinge region of the receptor <ref name="Faust">PMID: 35940205</ref>. This interaction is specific to TSH and TSHR. When other agonists or antagonists bind to the receptor, the change in conformation is a result of different residues interacting, as explained later in the page. The Leucine residues in the LRRD determine ECD folding and which residues are located on the exterior protein and interacting with ligands.

~~=== Active and Inactive Form ===~~

~~[[Image:Morph_pics2.png|200 px|right|thumb|Figure 2: Inactive form of the thyrotropin receptor shown in blue. Active form of the thyrotropin receptor shown in green.]]~~

The TSHR protein exists in two states: active and inactive (Figure 2) (GREEN LINK ?). The <scene name='95/952708/Tshr_chainr_ecd/1'>ECD</scene> protrudes from the cell membrane into the space outside the cell. The <scene name='95/952708/Tshr_chainr_tm/1'>transmembrane domain</scene> contains 7 alpha helices that reside within the cell membrane. The <scene name='95/952708/Tshr_chainr/4'>TSHR active form</scene> exists when bound to the <scene name='95/952708/Tsh_7t9i/1'>TSH</scene>. One proposed mechanism for the transition from the active to inactive describes that in a natural state, the TSHR ECD can spontaneously transition to the up state, leading to constitutive activity. In this active state, TSH will bind and keep the active state in the up position because of clash with the cell membrane.<ref name="Faust" /> Conformational change of ECD allows for signal transduction through the TM and into the cell. The ECD rotates 55 degrees up in the active form. <ref name="Faust" />

== TSHR Agonists and Antagonists ==

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 The ECD of TSHR is anchored to the membrane through seven transmembrane helices (7TMD), characteristic of GPCRs. Conformational changes in the 7TMD activate intracellular G-protein signaling<ref name= "Keinau et al.">Kleinau, G., Worth, C. L., Kreuchwig, A., Biebermann, H., Marcinkowski, P., Scheerer, P., &amp; Krause, G. (2017). Structural–functional features of the thyrotropin receptor: A class A G-protein-coupled receptor at work. Frontiers in Endocrinology, 8. https://doi.org/10.3389/fendo.2017.00086</ref>. Once TSH binds, changes to the p10 peptide are transmitted to the 7TMD. Specifically, hinge helix rotation causes  displacement of the p10 peptide that allows the <scene name='95/952709/Helix_7_of_7tmd/2'>seventh transmembrane helix (TM7)</scene> to migrate towards the center of the 7TMD to increase van Der Waals contacts. Additionally, K660 of TM7 forms a stabilizing <scene name='95/952709/Helix_7_and__p10_interaction/6'>ionic interaction</scene> with E409 of the p10 region. Hinge helix movement also rearranges Y279 relative to I486 on the neighboring <scene name='95/952709/Hinge_helix_ecl1/3'>extracellular loop 1 (ECL1) helix</scene>, which links two transmembrane helices and is located extracellularly. Substitution of these residues leads to substantial shifts in the activation of the thyrotropin receptor. Structurally guided mutagenic studies have shown that replacing isoleucine with a more sizeable phenylalanine decreases TSH signaling potency<ref name="Faust et al.">Faust, B., Billesbølle, C.B., Suomivuori, CM. et al. Autoantibody mimicry of hormone action at the thyrotropin receptor. Nature 609, 846–853 (2022). https://doi.org/10.1038/s41586-022-</ref><ref name="Vlaeminck-Guillem et al.">Virginie Vlaeminck-Guillem, Su-Chin Ho, Patrice Rodien, Gilbert Vassart, Sabine Costagliola, Activation of the cAMP Pathway by the TSH Receptor Involves Switching of the Ectodomain from a Tethered Inverse Agonist to an Agonist, Molecular Endocrinology, Volume 16, Issue 4, 1 April 2002, Pages 736–746, https://doi.org/10.1210/mend.16.4.0816</ref>.The sixth transmembrane helix of TSHR moves outward from the center of the 7TMD to facilitate α-helix 5 of the α-subunit of the G protein (Gα)<ref name="Faust et al.">Faust, B., Billesbølle, C.B., Suomivuori, CM. et al. Autoantibody mimicry of hormone action at the thyrotropin receptor. Nature 609, 846–853 (2022). https://doi.org/10.1038/s41586-022-</ref><ref name="Goricanec et al.">Goricanec, D., Stehle, R., Egloff, P., Grigoriu, S., Plückthun, A., Wagner, G., &amp; Hagn, F. (2016). Conformational dynamics of a G-protein α subunit is tightly regulated by nucleotide binding. Proceedings of the National Academy of Sciences, 113(26). https://doi.org/10.1073/pnas.1604125113 </ref>. Gα is activated for intracellular signaling when GDP is exchanged for GTP and dissociates from the γ- and β-subunits of the G-protein (Gγ and Gβ) to bind with other target proteins. Activation of the Gα is caused by conformational shifts in the 7TMD and three intracellular loops which directly interact with the G-protein<ref name= "Keinau et al.">Kleinau, G., Worth, C. L., Kreuchwig, A., Biebermann, H., Marcinkowski, P., Scheerer, P., &amp; Krause, G. (2017). Structural–functional features of the thyrotropin receptor: A class A G-protein-coupled receptor at work. Frontiers in Endocrinology, 8. https://doi.org/10.3389/fendo.2017.00086</ref>. Conformational shifts in transmembrane helices are the mechanism of changing interactions of the G-protein with the receptor. Activation of the G-protein is caused by these conformational shifts.
-=== Leucine Rich Repeats ===
-The Leucine Rich Repeat Domain (LRRD) is part of the <scene name='95/952708/Tshr_chainr_ecd/1'>ECD</scene> of TSHR and contains <scene name='95/952707/Lrr/3'>10-11 Leucine Rich Repeats</scene>. A unique feature of this region is that it is composed entirely of β-pleated sheets. These β-pleated sheets of the LRRD provides a concave binding surface for TSH, including <scene name='95/952707/Interactions_with_thyrotropin/2'>K209 and K58</scene> <ref name="Duan et al.">PMID: 35940204</ref>. These interact with <scene name='95/952707/Interactions_with_thyrotropin/2'>N91 and E98</scene> in the seatbelt region of TSH forming a salt bridge and initiating the conformational change by pulling on the hinge region of the receptor <ref name="Faust">PMID: 35940205</ref>. This interaction is specific to TSH and TSHR. When other agonists or antagonists bind to the receptor, the change in conformation is a result of different residues interacting, as explained later in the page. The Leucine residues in the LRRD determine ECD folding and which residues are located on the exterior protein and interacting with ligands.
-=== Active and Inactive Form ===
-[[Image:Morph_pics2.png|200 px|right|thumb|Figure 2: Inactive form of the thyrotropin receptor shown in blue. Active form of the thyrotropin receptor shown in green.]]
-The TSHR protein exists in two states: active and inactive (Figure 2) (GREEN LINK ?). The <scene name='95/952708/Tshr_chainr_ecd/1'>ECD</scene> protrudes from the cell membrane into the space outside the cell. The <scene name='95/952708/Tshr_chainr_tm/1'>transmembrane domain</scene> contains 7 alpha helices that reside within the cell membrane. The <scene name='95/952708/Tshr_chainr/4'>TSHR active form</scene> exists when bound to the <scene name='95/952708/Tsh_7t9i/1'>TSH</scene>. One proposed mechanism for the transition from the active to inactive describes that in a natural state, the TSHR ECD can spontaneously transition to the up state, leading to constitutive activity. In this active state, TSH will bind and keep the active state in the up position because of clash with the cell membrane.<ref name="Faust" /> Conformational change of ECD allows for signal transduction through the TM and into the cell. The ECD rotates 55 degrees up in the active form. <ref name="Faust" />
 == TSHR Agonists and Antagonists ==