In medium-size, spiny striatal neurons of the direct pathway, dopamine D₁- and adenosine A₁-receptors are coexpressed and are mutually antagonistic. Recently, a mutation in the gene encoding the A₁-receptor (A₁R), A₁R-G279S^7.44, was identified in an Iranian family: two affected offspring suffered from early-onset l-DOPA–responsive Parkinson’s disease. The link between the mutation and the phenotype is unclear. Here, we explored the functional consequence of the G279S substitution on the activity of the A₁-receptor after heterologous expression in HEK293 cells. The mutation did not affect surface expression and ligand binding but changed the susceptibility to heat denaturation: the thermodynamic stability of A₁R-G279S^7.44 was enhanced by about 2 and 8 K when compared with wild-type A₁-receptor and A₁R-Y288A^7.53 (a folding-deficient variant used as a reference), respectively. In contrast, the kinetic stability was reduced, indicating a lower energy barrier for conformational transitions in A₁R-G279S^7.44 (73 ± 23 kJ/mol) than in wild-type A₁R (135 ± 4 kJ/mol) or in A₁R-Y288A^7.53 (184 ± 24 kJ/mol). Consistent with this lower energy barrier, A₁R-G279S^7.44 was more effective in promoting guanine nucleotide exchange than wild-type A₁R. We detected similar levels of complexes formed between D₁-receptors and wild-type A₁R or A₁R-G279S^7.44 by coimmunoprecipitation and bioluminescence resonance energy transfer. However, lower concentrations of agonist were required for half-maximum inhibition of dopamine-induced cAMP accumulation in cells coexpressing D₁-receptor and A₁R-G279S^7.44 than in those coexpressing wild-type A₁R. These observations predict enhanced inhibition of dopaminergic signaling by A₁R-G279S^7.44 in vivo, consistent with a pathogenic role in Parkinson’s disease.

中文翻译：

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G279S取代在腺苷A1受体（A1R-G279S7.44）（与帕金森氏病有关的突变）中的功能影响

在直接通路的中型棘状纹状体神经元中，多巴胺D _1-和腺苷A _1-受体共表达且相互拮抗。最近，在一个伊朗家庭中发现了编码A ₁受体（A ₁ R）（A ₁ R-G279S ^7.44）的基因中的一个突变：两个受影响的后代患有早发性1 -DOPA反应性帕金森氏病。突变与表型之间的联系尚不清楚。在这里，我们探讨了G279S取代对A ₁活性的功能影响HEK293细胞中异源表达后的β-受体。该突变不影响表面表达和配体结合，但改变了对热变性的敏感性：与野生型A ₁受体和A ₁ R相比，A ₁ R-G279S ^7.44的热力学稳定性提高了约2和8K。-Y288A ^7.53（用作参考的折叠缺陷型）。相反，动力学稳定性降低了，表明与野生型A ₁ R（135±4 kJ / mol）或在A ₁ R-G279S ^7.44（73±23 kJ / mol）中构象转变的能垒相比，较低一个₁ R-Y288A ^7.53（184±24kJ / mol）。与这种较低的能垒一致，A ₁ R-G279S ^7.44在促进鸟嘌呤核苷酸交换方面比野生型A ₁ R更有效。我们检测到D ₁受体与野生型A ₁ R或A之间形成的复合物水平相似₁ R-G279S ^7.44通过共免疫沉淀和生物发光共振能量转移。然而，与共表达野生型A _1的细胞相比，在共表达D ₁受体和A ₁ R-G279S ^7.44的细胞中半峰抑制多巴胺诱导的cAMP积累所需的激动剂浓度更低。R.这些观察结果预测A ₁ R-G279S ^7.44在体内对多巴胺能信号传导的抑制作用增强，这与帕金森氏病的致病作用一致。