Molecular Mechanism of Ca²⁺ in the Allosteric Regulation of Human Parathyroid Hormone Receptor-1

Abstract

Parathyroid hormone (PTH) is an endogenous ligand that activates the PTH type 1 receptor (PTH1R) signaling. Ca2+, a common second messenger, acts as an allosteric regulator for prolonging the activation of PTH1R. However, a clear picture of the underlying allosteric mechanism is still missing. Herein, extensive molecular dynamics (MD) simulations are performed for PTH1R-PTH complexes with and without Ca2+ ions, allowing us to delineate the molecular details of calcium-induced allostery. Our results indicate that acidic residues in the extracellular loop 1 (ECL1) (D251, E252, E254, and E258–E260) and PTH (E19 and E22) serve as key determinants for local Ca2+-coupling structures and rigidity of ECL1. Moreover, the binding of Ca2+ induces conformational changes of transmembrane domain 6/7 (TM6/7) that are related to PTH1R activation and strengthens the residue–residue communication within PTH and TMD allosterically. Moreover, our results demonstrate that the presence of Ca2+ ions potentiates the interaction between PTH and PTH1R via steered molecular dynamics (SMD) simulations, while the point mutation in the PTH (PTHR25C) weakens the binding of PTH and PTH1R. These results support that Ca2+ ions might further prolong the residence time of PTH on PTH1R and facilitate the positive allostery of PTH1R. Together, the present work provides new insights into the allosteric regulation mechanism of GPCRs induced by ions and related drug design targeting the PTH1R allosteric pathway.

Proteolytic Cleavage of the Extracellular Domain Affects Signaling of Parathyroid Hormone 1 Receptor

“…Apart from PARs and adhesion receptors, where the buried ligand is proteolytically released from the receptor's Nterminus, extracellular loops play an important role in modulating the function of several class A and class B receptors (50). More importantly, calcium-mediated interaction of extracellular loop 1 and PTH has been shown to modulate PTH1R activity (51)(52)(53). Recent studies on glucagon receptor suggest that the ECD itself may act as an allosteric inhibitor by interaction of a1-helix of the ECD with extracellular loop 3 of the receptor core (54).…”

Critical Extracellular Ca2+ Dependence of the Binding between PTH1R and a G-Protein Peptide Revealed by MD Simulations

“…After 1000 ns full complex MD simulations, stable coupling conformations of Ca 2+ , ECL1, and PTH were observed consistent with our previous study. 24 First, the convergence of MD trajectories was monitored by the root-mean-square deviations (RMSDs) of all Cα atoms of the seven-transmembrane (7TM) helices from their initial coordinates. As illustrated in Figure S1, all simulations converged within 1000 ns, especially the last 300 ns.…”

“…Molecular Dynamics Simulation. As previously described, 24 the molecular dynamics simulations of four systems were carried out using the AMBER18 package. 36 The cutoff distance for nonbonded interactions was set to 10 Å, 37 and the SHAKE 38 method was used to constrain bonds involving hydrogen.…”

“…23 Our previous work demonstrated that acidic residues in the extracellular loop 1 (ECL1) (D251, E252, E254, and E258− E260) and PTH (E19 and E22) constituted the stable local Ca 2+ -coupling structures by extensive molecular dynamics (MD) simulations (Figure 1), and the presence of Ca 2+ ions strengthened the communications within PTH and the transmembrane domain (TMD) and enhanced the activation of PTH1R. 24 release of calcium stored in the bone causes large dynamic fluctuations of calcium concentration, 25 and PTH is the key hormone to regulate the calcium level. 26 Therefore, the calcium balance might be ensured by promoting the catabolic actions of PTH through the Ca 2+ allostery.…”

Proteolytic cleavage of the extracellular domain affects signaling of parathyroid hormone receptor 1

“…Apart from PARs and adhesion receptors, where the buried orthosteric ligand is proteolytically released from the receptor's N-terminus, extracellular loops play an important role in modulating the function of several class A and class B receptors (49). More importantly, calcium-mediated interaction of extracellular loop 1 and PTH has been shown to allosterically modulate PTH1R activity (50)(51)(52). Recent studies on glucagon receptor suggest that the ECD itself may act as an allosteric inhibitor by interaction of α1-helix of the ECD with extracellular loop 3 of the receptor core (53).…”