Human Parathyroid Hormone Receptor 2

Ellie Manning '26 and Linnea Parker '25

Contents:

I. Introduction

Parathyroid hormone receptor 2 (PTH2R) is one of two types of parathyroid hormone receptors mediated by coupling to the stimulatory G protein. All parathyroid hormone receptors have three endogenous ligands. PTH2R has TIP39 (tuberoinfundibular peptide), PTH (parathyroid hormone), and PTHrP (parathyroid hormone related peptide). PTH2R interacts and regulates TIP39 most potently of the three, and unlike PTH1R interacts only weakly with PTH. The formation of the TIP39-bound PTH2R complex allows for the binding of a G protein, which stimulates the complex and allows for the binding of a ligand. While the exact functions of PTH2R are not known, it is thought to play a role in nociception mediation, calcium transportation, wound healing, and maternal behavior. Mutations to PTH2R have been reported in relation to heritable diseases such as osteoarthritis, syndromic intellectual disability, and syndromic short stature. The structure of human PTH2R was determined in complex with TIP39 and a heterotrimeric GS protein via cryogenic electron microscopy.

II. General Structure

The PTH2R-GS complex contains the first 34 amino acids of TIP39, the PTH2R, a dominant negative human G-alpha-s including 8 mutations, rat G-beta-1, G-gamma-2, and nanobody Nb35. The inclusion Gs heterotrimer (composed of G-𝛼-s, β-1, and G-gamma-2) and the antibody Nb35 allow for us to visualize and understand how PTH2R forms bonds and interacts with its various ligands. A notable difference between this complex and other activated class B1 GPCRs occurs in the transmembrane domain (TMD) ligand-binding pocket, as TIP39 exhibits a single amphipathic alpha-helix from Leu4P (the deepest residue within the receptor core) to Leu34P. Additionally, the helix adopts a closed loop at the peptide N terminus that facilitates a deep insertion of the peptide into the receptor core and participates in PTH2R activation via interactions with TM5 and TM6. The extended TM1 helix makes the structure capable of interacting with a peptidic ligand, and undergoes slight conformational changes to accommodate each individual receptor. Another conformational change occurs when creating the PTH2R-GS interface. The outward movement of TM6 leads to a large opening of the cytoplasmic cavity, making it available for GS coupling.

III. Receptor Binding

The PTH2R-GS complex is anchored with the alpha-5 helix of G-alpha-s which fits snugly into the cavity of the TMD, and has a number of polar and nonpolar interactions. These interactions allow for the binding of various ligands to the complex. The side chain of Glu392 and the last helical residue of the alpha-5 helix Ser364 form a capping interaction with backbone amine of helix 8 through polar bonds. Arg385 and Asp381 at the middle of the alpha-5 helix in G-alpha-s make charged interactions with Glu356ICL3 and Lys3435.64b of TM5. The carboxylate group at the C-terminal end of the alpha-5 helix in G-alpha-s forms a salt bridge with Lys3606.37b of TM6. Hydrophobic residues Leu388, Tyr391, Leu393, and Leu394 pack tightly against the hydrophobic surface comprised of residues of TM2, TM3, TM5, TM6, and TM7. The alpha-5 helix of G-alpha-s interacts with the intracellular crevice of the PTH2R TMD and helix 8 of PTH2R.

To specifically accommodate TIP39, PTH2R reforms its peptide-binding pocket by reorganizing the conformations of ECL3 and the extracellular parts of TM1 and TM7, and adopts receptor-specific amino acids at multiple positions that directly interact with the peptide. The extracellular tip of TM7 shifts outward, decreasing contacts with TIP39. The extracellular tip of TM1 in PTH2R is extended by six residues, allowing the formation of a hydrogen bond between Gln130 1.25B and Arg23P. PTH2R uses a polar residue Tyr318 5.39b to form hydrogen bonds with Asp7P and Arg11P of TIP39.

IV. Medical Functions and Implications

Very little is understood about PTH2R and its functions in the body. PTH2R is expressed throughout the central and peripheral nervous systems, though highest in the brain, and is thought to be a mediator of nociception, and involved in lactation, stress and fear response, and body temperature. Medical conditions linked to PTH2R function include osteoarthritis, syndromic intellectual disability, and syndromic short stature. PTH2R has been found to elevate cAMP and Ca2+ levels. Of the three endogenous ligands, and in contrast to PTH1R, PTH2R mostly strongly interacts with TIP39, and only weakly interacts with PTH. PTH2R and TIP39 have been proposed as a neuroendocrine regulation system, and based on location of expression in the brain, researchers have been able to infer what PTH2R might be involved in. A review paper, Dobolyi et al. 2012, examines notable experiments in determining the functions of TIP39. For example, Wang et al. 2021 created a deletion in TIP39 to imitate the naturally occurring G258D mutation implicated with syndromic short stature. This deletion was observed to significantly affect cAMP signaling because it prevents critical interactions between the unique N terminus loop of TIP39 and PTH2R. Another study, Dimitrov et al. 2013, performed TIP39 and PTH2R knockouts on mice and found that both mice models were less sensitive to pain. 

V. References

1. Dimitrov, E. L., Kuo, J., Kohno, K., & Usdin, T. B. (2013). Neuropathic and inflammatory pain are modulated by tuberoinfundibular peptide of 39 residues. Proceedings of the National Academy of Sciences of the United States of America, 110(32), 13156–13161. https://doi.org/10.1073/pnas.1306342110

2. Dobolyi, A., Dimitrov, E., Palkovits, M., & Usdin, T. B. (2012). The neuroendocrine functions of the parathyroid hormone 2 receptor. Frontiers in endocrinology, 3, 121. https://doi.org/10.3389/fendo.2012.00121

3. Kobayashi, K., Kawakami, K, Kusakizako, T., Miyauchi, H., Tomita, A., Kobayashi, K., Shihoya, W., Yamashita, K., Nishizawa, T., Kato, H., Inoue, A, & Nureki, O. (2022). Endogenous ligand recognition and structural transition of a human PTH receptor. Molecular Cell 82, 3468–3483. https://doi.org/10.1016/j.molcel.2022.07.003

4. Meulenbelt, I., Min, J. L., van Duijn, C. M., 4. Kloppenburg, M., Breedveld, F. C., & Slagboom, P. E. (2006). Strong linkage on 2q33.3 to familial early-onset generalized osteoarthritis and a consideration of two positional candidate genes. European journal of human genetics : EJHG, 14(12), 1280–1287. https://doi.org/10.1038/sj.ejhg.5201704

5. Wang, X., Cheng, X., Zhao, L., Wang, Y., Ye, C., Zou, X., Dai, A., Cong, Z., Chen, J., Zhou, Q., Xia, T., Jiang, H., Xu, H. E., Yang, D., & Wang, M. W. (2021). Molecular insights into differentiated ligand recognition of the human parathyroid hormone receptor 2. Proceedings of the National Academy of Sciences of the United States of America, 118(32), e2101279118. https://doi.org/10.1073/pnas.2101279118

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