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Mathematical analysis of the sodium sensitivity of the human histamine H 3 receptor

View Article: PubMed Central - PubMed

ABSTRACT

Purpose: It was shown by several experimental studies that some G protein coupled receptors (GPCR) are sensitive to sodium ions. Furthermore, mutagenesis studies or the determination of crystal structures of the adenosine A2A or δ-opioid receptor revealed an allosteric Na+ binding pocket near to the highly conserved Asp2.50. Within a previous study, the influence of NaCl concentration onto the steady-state GTPase activity at the human histamine H3 receptor (hH3R) in presence of the endogenous histamine or the inverse agonist thioperamide was analyzed. The purpose of the present study was to examine and quantify the Na+-sensitivity of hH3R on a molecular level.

Methods: To achieve this, we developed a set of equations, describing constitutive activity and the different ligand-receptor equilibria in absence or presence of sodium ions. Furthermore, in order to gain a better understanding of the ligand- and Na+-binding to hH3R on molecular level, we performed molecular dynamic (MD) simulations.

Results: The analysis of the previously determined experimental steady-state GTPase data with the set of equations presented within this study, reveals that thioperamide binds into the orthosteric binding pocket of the hH3R in absence or presence of a Na+ in its allosteric binding site. However, the data suggest that thioperamide binds preferentially into the hH3R in absence of a sodium ion in its allosteric site. These experimental results were supported by MD simulations of thioperamide in the binding pocket of the inactive hH3R. Furthermore, the MD simulations revealed two different binding modes for thioperamide in presence or absence of a Na+ in its allosteric site.

Conclusion: The mathematical model presented within this study describes the experimental data regarding the Na+-sensitivity of hH3R in an excellent manner. Although the present study is focused onto the Na+-sensitivity of the hH3R, the resulting equations, describing Na+- and ligand-binding to a GPCR, can be used for all other ion-sensitive GPCRs.

No MeSH data available.


Sodium sensitivity oh hH3R. A, Structures of histamine and thioperamide. B, Influence of sodium ions onto the hH3R, determined in the steady state GTPase assay. (Figure was adopted from Schnell and Seifert (2010).
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Fig1: Sodium sensitivity oh hH3R. A, Structures of histamine and thioperamide. B, Influence of sodium ions onto the hH3R, determined in the steady state GTPase assay. (Figure was adopted from Schnell and Seifert (2010).

Mentions: During the last decades, several theoretical models were established to explain receptor function quantitatively (Leff 1995; Leff et al. 1997; Christopoulos and Kenakin 2002; Kenakin 2004; Langmead and Christopoulos 2006; Kenakin 2013). Those basic concepts can be extended to describe ion-sensitivity of GPCRs. Within a previous study of Schnell and Seifert (2010), the influence of NaCl concentration onto the concentration response curves of the endogenous histamine and the inverse agonist thioperamide onto the hH3R were investigated (Figure 1). Within the present study, we developed a set of equations, describing constitutive activity and the different ligand-receptor equilibra in presence or absence of sodium ions. Furthermore, we used the experimental data, published by Schnell and Seifert (2010) previously (Figure 1) for determination of the equilibrium constants, described by the set of equations, mentioned above, e.g. constants regard to constitutive activity, binding of a sodium ion to the receptor, and binding of histamine or thioperamide to the hH3R in absence or presence of sodium ions. Furthermore, MD simulations of several inactive thioperamide-Na+-hH3R-complexes were performed. These simulations showed that thioperamide can bind into the orthosteric site of hH3R in presence or absence of the Na+ in the allosteric pocket, resulting in different binding modes of thioperamide.Figure 1


Mathematical analysis of the sodium sensitivity of the human histamine H 3 receptor
Sodium sensitivity oh hH3R. A, Structures of histamine and thioperamide. B, Influence of sodium ions onto the hH3R, determined in the steady state GTPase assay. (Figure was adopted from Schnell and Seifert (2010).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4644138&req=5

Fig1: Sodium sensitivity oh hH3R. A, Structures of histamine and thioperamide. B, Influence of sodium ions onto the hH3R, determined in the steady state GTPase assay. (Figure was adopted from Schnell and Seifert (2010).
Mentions: During the last decades, several theoretical models were established to explain receptor function quantitatively (Leff 1995; Leff et al. 1997; Christopoulos and Kenakin 2002; Kenakin 2004; Langmead and Christopoulos 2006; Kenakin 2013). Those basic concepts can be extended to describe ion-sensitivity of GPCRs. Within a previous study of Schnell and Seifert (2010), the influence of NaCl concentration onto the concentration response curves of the endogenous histamine and the inverse agonist thioperamide onto the hH3R were investigated (Figure 1). Within the present study, we developed a set of equations, describing constitutive activity and the different ligand-receptor equilibra in presence or absence of sodium ions. Furthermore, we used the experimental data, published by Schnell and Seifert (2010) previously (Figure 1) for determination of the equilibrium constants, described by the set of equations, mentioned above, e.g. constants regard to constitutive activity, binding of a sodium ion to the receptor, and binding of histamine or thioperamide to the hH3R in absence or presence of sodium ions. Furthermore, MD simulations of several inactive thioperamide-Na+-hH3R-complexes were performed. These simulations showed that thioperamide can bind into the orthosteric site of hH3R in presence or absence of the Na+ in the allosteric pocket, resulting in different binding modes of thioperamide.Figure 1

View Article: PubMed Central - PubMed

ABSTRACT

Purpose: It was shown by several experimental studies that some G protein coupled receptors (GPCR) are sensitive to sodium ions. Furthermore, mutagenesis studies or the determination of crystal structures of the adenosine A2A or δ-opioid receptor revealed an allosteric Na+ binding pocket near to the highly conserved Asp2.50. Within a previous study, the influence of NaCl concentration onto the steady-state GTPase activity at the human histamine H3 receptor (hH3R) in presence of the endogenous histamine or the inverse agonist thioperamide was analyzed. The purpose of the present study was to examine and quantify the Na+-sensitivity of hH3R on a molecular level.

Methods: To achieve this, we developed a set of equations, describing constitutive activity and the different ligand-receptor equilibria in absence or presence of sodium ions. Furthermore, in order to gain a better understanding of the ligand- and Na+-binding to hH3R on molecular level, we performed molecular dynamic (MD) simulations.

Results: The analysis of the previously determined experimental steady-state GTPase data with the set of equations presented within this study, reveals that thioperamide binds into the orthosteric binding pocket of the hH3R in absence or presence of a Na+ in its allosteric binding site. However, the data suggest that thioperamide binds preferentially into the hH3R in absence of a sodium ion in its allosteric site. These experimental results were supported by MD simulations of thioperamide in the binding pocket of the inactive hH3R. Furthermore, the MD simulations revealed two different binding modes for thioperamide in presence or absence of a Na+ in its allosteric site.

Conclusion: The mathematical model presented within this study describes the experimental data regarding the Na+-sensitivity of hH3R in an excellent manner. Although the present study is focused onto the Na+-sensitivity of the hH3R, the resulting equations, describing Na+- and ligand-binding to a GPCR, can be used for all other ion-sensitive GPCRs.

No MeSH data available.